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Copyright copy 2011 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 11 2652ndash2656 2011

Morphology and Magnetic Characterisation ofAluminium Substituted Yttrium-Iron Garnet

Nanoparticles Prepared Using Sol Gel Technique

Noorhana Yahya1lowast Ramadan Masoud Al Habashi2 Krzysztof Koziol3Rafal Dunin Borkowski3 Majid Niaz Akhtar1 Muhammad Kashif1 and Mansor Hashim2

1Electrical and Electronic Engineering Department and Department of Fundamental and Applied SciencesUniversiti Teknologi PETRONAS Bandar Seri Iskandar 31750 Tronoh Perak Malaysia

2Department of Physics Faculty of Science and Advanced Materials and Nanotechnology Laboratory (AMNL)Institute of Advanced Technology (ITMA) Universiti Putra Malaysia 43400 UPM Serdang Selangor Malaysia

3Department of Materials Science and Metallurgy University of Cambridge CB2 3 QZ England United Kingdom

Aluminum substituted yttrium iron garnet nano particles with compositional variation ofY30minusx AlxFe5O12 where x = 000510152025 and 30 were prepared using sol gel tech-nique The X-ray diffraction results showed that the best garnet phase appeared when the sinteringtemperature was 800 C Nano-crystalline particles with high purity and sizes ranging from 20 to100 nm were obtained It was found that the aluminum substitution had resulted in a sharp fall of thed-spacing when x = 2 which we speculated is due to the preference of the aluminum atoms to thesmaller tetrahedron and octahedron sites instead of the much larger dodecahedron site High res-olution transmission electron microscope (HRTEM) and electron diffraction (ED) patterns showedsingle crystal nanoparticles were obtained from this method The magnetic measurement gavemoderate values of initial permeability the highest value of 53 was shown by sample Y3Fe5O12 atmore than 100 MHz which was attributed to the morphology of the microstructure which appearedto be homogeneous This had resulted in an easy movement of domain walls The substitutionof aluminum for yttrium is speculated to cause a cubic to rhombodedral structural change andhad weakened the super-exchange interactions thus a fall of real permeability was observed Thismight have created a strain in the sub-lattices and had subsequently caused a shift of resonancefrequencies to more than 18 GHz when x gt 05

Keywords Electron Diffraction Super-Exchange Interactions Real Permeability Single CrystalTetrahedron

1 INTRODUCTION

Magnetic garnet namely yttrium iron garnet (Y3Fe5O12that belongs to a group of magnetic oxides is anattractive material for magneto-optical devices They alsohave important applications within microwave frequenciesnamely optical isolators oscillators circulators and so ondue to their large Faraday rotation and high saturationmagnetization1 For these reasons there are ongoing inter-ests in investigating the chemical physical and magneticproperties of these garnet materials The preparation tech-niques and the judicious choice of chemical compositionsare important to arrive at the desired magnetic properties

lowastAuthor to whom correspondence should be addressed

to meet the practical utilisation mentioned as well as tostudy their fundamental propertiesThe common method for ceramic powder synthesis of

garnet is the grinding of mixed oxide starting powdersfollowed by a solid state reaction2 This method howeverrequires high temperature to form single phase garnet crys-tal Additionally this method also produces particles hav-ing large size most likely more than a micrometer andlimited degree of homogeneity This is not favorable asmost researchers are currently moving towards the nano-size garnet materials The sol gel technique seems to beone of the most popular methods since it allows the finalnanocrystals to have narrow size distribution Attemptsto produce YIG using the sol gel technique have beenreported extensively by many researchers3ndash4

2652 J Nanosci Nanotechnol 2011 Vol 11 No 3 1533-48802011112652005 doi101166jnn20112723

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Yahya et al Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique

The premise of this work focuses on vigorous andsystematic investigation on the garnets having a gen-eral chemical formula of Y3Fe5O12 Aluminum was usedto replace yttrium having stoichiometric composition ofY3minusxAlxFe5O12 with x= 00051015 20 25 and 30by sol gel preparation method The choice of the alu-minum to replace iron for YAG5ndash6 has been done quiteextensively However using aluminum to replace yttriumhas not been reported This was carried out to see whetherthe magnetic properties of the garnet due to the triva-lent Fe ion (Fe3+ that has a moment equivalent to fiveuncompensated spins7 can be retained When the iron iscombined with yttrium and aluminum in a metallic crys-tal the atomic moments are spontaneously held in parallelalignment over regions within each crystallite The regionsin which alignment occurs are called domains which mayextend over many thousands of unit cells8 In consequenceby changing the garnet compositions with the substitutionof aluminum it is possible to alter the structural and hencethe magnetic properties of the garnet system These parti-cles have potential application as magnetic sensor

2 EXPERIMENTAL PROCEDURE

The starting solution is a mixture of iron nitrateFe(NO33 middot9H2O yttrium nitrate Y(NO33 middot6H2O and alu-minum nitrate Al(NO33 middot 9H2O which were dissolved in150 mL of citric acid C6H8O7 middotH2O The mixtures werestirred continuously at about 250 rpm in room tempera-ture until the formation of gel was observed This processwas carried out for one month The gel was dried at 110 Cin an oven to remove the unneeded water The dried pow-der was calcined at 600 C for 3 hours in air and was wetcrushed using a Fritsch Planetary Micro mill for 6 hours toobtain a fine particle powder Subsequently they were sin-tered at 600 C 700 C 800 C and 900 C for 3 hours inair They were characterized by X-ray diffraction (PhilipsXrsquopert PRO PW 3040 PAN Analytical) to confirm the bestgarnet phase Field emission scanning electron microscopy(FESEM SUPRA 35 VP) low resolution transmissionelectron microscope (JOEL JEM CX 200) and high reso-lution transmission electron microscope (FEI Tecnai F20)with 200 kV field emission gun (FEG) were used to studythe morphology and the d-spacing of some of the sam-ples ImageJ software that runs under Linux was used tomeasure the length of the d-spacing A magnetic prop-erty real permeability analysis was carried out using anRF Impedance Analyzer (Agilent 4291B) in the frequencyrange of 10 MHzndash18 GHz

3 RESULTS AND DISCUSSION

X-ray diffraction with CuK radiation K = 089 andwavelength = 154056 Aring was used to determine thecrystal structure of aluminum substituted yttrium iron

garnet samples at different calcining temperatures from600 C to 900 C The unit cell size and geometry wereresolved from the angular positions of the diffractionpeaks whereas arrangement of atoms within the unit cellis associated with the relative intensities of these peaksFrom the X-ray diffraction patterns of the Al-YIG sin-

tered samples at 800 C for 3 hours in air (Fig 1) it wasfound that fully crystalline yttrium iron garnet had beenformed in the Y3Fe5O12 sample The sharp peaks observedindicate high crystallinity of the samples the highest inten-sity that comes from (420) plane from the yttrium irongarnet is 9515 (Fig 1 and Table I) This peak was also pre-viously observed by other researchers6 It is obvious thatthe correct sintering temperature is one of the main factorsaffecting the formation of the garnet phase for all the sam-ples The highest count (4158) for aluminum iron garnetsample was also observed when the sample was sinteredat 800 C Details on the major peaks their intensities andthe d-spacing are given in Table I The substitution of alu-minum to yttrium had resulted in a clear shift of the majorpeak from (420) plane to (104) plane We speculate that itis attributed to the partial occupancy by aluminum ions ofthe tetrahedron and octahedron8ndash10 instead of the dodeca-hedron sites This is due to the fact that aluminum has amuch smaller ionic radius (0530 Aring) compared to that ofyttrium (0892 Aring) The larger dodecahedron sites (240 Aring)are more suitable for the large yttrium ions When morealuminum ions are replace the yttrium they tend to occupythe octahedron (201 Aring) and the tetrahedron (187 Aring) sitesinstead of the dodecahedron site Due to the smaller sizeof the shift from the (420) plane to (104) plane as wellas the observation of two major peaks (Fig 1) located at(420) and (104) planes for sample with x= 15 strengthensthe speculations made with regard to the occupancies ofthese cations It should be noted that there is a sharp fallof d-spacing (Table I) at the major peaks when x = 20which we attributed to the occupancy of more aluminumto the tetrahedron and octahedron sites When lower molefraction of yttrium occupies the dodecahedron site there is

Fig 1 XRD pattern of Al-YIG samples sintered at 800 C

J Nanosci Nanotechnol 11 2652ndash2656 2011 2653

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Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

Table I Intensity and 2-theta for Al-YIG samples sintered at 800 C

Mole 2-Theta Intensity d-spacing Av d-spacing hkl

fraction (x) (deg) (au) (Aring) (Aring) (major peak)

00 3234 951500 277 277 42005 3245 695500 276 276 42010 3263 465600 274 274 42015 3270 279600 273 274 42020 3322 330018 270 270 10425 3324 314700 270 270 10430 3330 415800 269 270 104

a shrink of the mentioned site and the total garnet struc-ture A closer look at Figure 1 reveals a slight gradual shiftof the major peak to higher 2-theta at (420) plane Thisindicates that a slight change of the position of some atomsin a systematic manner had caused this effect It couldbe speculated that when more aluminum replaces yttriumtwo major changes might had happened First the decreaseof yttrium from the dodecahedron site had caused a slightshrink to this sub-lattice and secondly the increment ofaluminum at the smaller octahedron and tetrahedron sitesmight have given a slight distortion to the major (420)plane of the lattice The slight move to the higher 2-thetaangle (Fig 1) indicates a smaller cell volume which isin accord with the speculation made Interesting howeveris the stable peak at plane (104) for x = 2025 and 30possibly due to the stable rhombohedron structure formedIt is significant to note that the sol gel technique gaveexcellent results of the Al-YIG samplesFESEM micrographs of the crystalline yttrium iron gar-

net sample sintered at 800 C for 3 hours in air are shownin Figure 2 From the FESEM micrographs in Figure 2 itcan be observed that when more aluminum is substitutingyttrium x = 20 and 25 clear cubic-like structure can beobserved (Fig 2) which we speculated to be single crystalstructure of garnet The average size of the morphology ofthe Al-YIG substitution can be observed in Table IIThe corresponding EDX results of sample Y3Fe5O12

shows that the oxygen iron and yttrium elements arewith atomic percentages of 5521 2577 and 1902respectively (Table II) No impurities were observed dueto the high purity starting materials of the sample compo-sition and stringent control of the preparation proceduresThe atomic of ferum to oxygen is a constant as what

x = 20 x = 25

Fig 2 Field emission scanning electron microscopy for samplesY3minusxAlxFe5O12 where x = 20 and 25 sintered at 800 C

Table II Summary of atomic and grain size for Al-YIG samplessintered at 800 C

Atomic

Mole Oxygen Aluminium Ferum Yttrium Grain sizefraction (x) (K) (K) (L) L (nm)

00 5521 000 2577 1902 82105 5769 202 2939 1090 57810 5528 499 2780 1192 55915 5747 695 2729 829 25220 5930 706 2722 642 46525 5688 898 3213 201 64230 5937 1306 2757 000 553

we expected Compared to oxygen the higher peak oxy-gen in the spectrum indicated more concentration of oxy-gen comparing to the ferum element as in the formulaY3minusxAlxFe5O12 Table II shows the atomic of yttriumversus mole fraction for the Al-YIG samples sintered at800 C which was extracted from the EDX data There isa gradual fall of yttrium and a consistent rise of atomicof yttrium On the other hand since we did not change themole fraction of the ferum and the oxygen of the Al-YIGthere is a constant atomic of both these elementsThe FESEM (Fig 2) images for samples with x = 20

and x = 25 that exhibit a cubic-like single crystal struc-tures had attracted our interest Further analysis was doneusing high resolution transmission electron microscopy(HRTEM) Observing Figure 3 for x = 20 the size of theparticles show an average d-spacing of 366 Aring Extract-ing the data of d-spacing from the XRD data (Fig1)we correspond this to the (012) plane The average par-ticle size of sample with x = 20 and x = 25 is 430 Aringand 465 Aring obtained from HRTEM and FESEM respec-tively The difference between the particle size obtainedfrom those of the HRTEM and FESEM micrographs isjust about 8 On the other hand sample with x = 25showed an average d-spacing of about 273 Aring The aver-age particle size of sample with x = 25 is 563 Aring and642 Aring obtained from HRTEM and FESEM respectivelyThis is about 14 difference obtained between those of theFESEM to the HRTEM micrographs It should be notedthat average d-spacing obtained from the HRTEM image

d-spacing366 Aring(012)

430 Aring

Particle size(average)

d-spacing273 Aring(104)

563 Aring

Particle size(average)

Fig 3 Particle size and d-spacing of samples Y3minusxAlxFe5O12 wherex = 20 and 25 taken by HRTEM

2654 J Nanosci Nanotechnol 11 2652ndash2656 2011

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RESEARCH

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Yahya et al Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique

X = 25X = 2X = 0

Fig 4 Electron Diffraction of samples Y3minusxAlxFe5O12 where x = 0020 and 25 taken by Transmission Electron Microscope

comparing with that of the XRD data is in good agreementwith about 1 of difference Figure 4 shows the electrondiffraction pattern of the samples with x = 00 20 and25 This result is consistent with the aforementioned factthe formation of single crystal of the samples that wereprepared via sol gel techniqueAn RF Impedance analyzer (Agilent 4291B) measure-

ment was used to study the magnetic properties of alu-minum substituted yttrium iron garnet samples at sinteredat 800 C for 3 hours in air The measurements of the realpermeability as a function of frequency for all the Al-YIGsamples were done at room temperature using toroid shapesamplesThe real permeability (prime) increases monotonically with

frequency for sample Y3Fe5O12 Obvious resonance peakdue to nature resonance phenomena can be observed in thespectrum at about 300 MHz However beyond 300 MHzthe real permeability starts to decrease rapidly Above thispoint the magnetic moments tend to absorb the energyfrom the external wave anticipating occurrence of spinndashspin interactions as well as spin lattice interactions Thehigher magnetic permeability compared to all the othersamples is due to the easy movement of domain walls asa result of the large grain size This is in good agreementwith FESEM results of the samples The substitution ofaluminum to yttrium when x = 05 shows a fall of realpermeability but an increase of resonance frequency Aswe expected the substitution of non magnetic ions suchas aluminum will result in a weakening of super-exchangeinteractions which resulted to the fall of the real perme-ability values For sample Y25Al05Fe5O12 the real perme-ability values prime increases monotonically with frequencyand when resonance occurred at about 300 MHz it tendsto fall abruptly Real permeability falls and resonance fre-quencies are shifted towards higher values for the rest ofthe Al-YIG samples It has to be noted that the resonancefrequencies of samples with mole fraction gt05 cannot beobserved due to the limitation of the Impedance AnalyzerThe extremely high resonance is speculated to be due tothe fact that aluminum ions are occupying the smallertetrahedron and octahedron sub-lattices as mentioned pre-viously (see X-ray results Fig 1) This is speculated toresult a strain and lattice distortion in both the tetrahedronand the octahedron sub-latticesIt is clearly demonstrated that the operating frequency

range strongly depends on the particle size As the particlesize decrease the operating frequency is shifted to higher

Fig 5 Real permeability versus frequency (Hz) for Al-YIG samples

value (Fig 5) This strengthens the speculations made withregard to the occupancies of the aluminum ions Hencethe desired operating frequency range can be achieved bytailoring the size of the particles in the materials due tothe choice of the preparation method namely the solndashgeltechnique Choosing the desired substitution material suchas aluminum to replace yttrium in the YIG samples willresult in high operating frequencies We intend to use thenano-particle as magnetic sensors for deep water oil andgas exploration

4 CONCLUSION

We had successfully prepared single crystal yttrium irongarnet and aluminium-yttrium iron garnet using a sol geltechnique The long stirring time allows the formation ofsingle crystal garnet structure The substitution of alu-minium to yttrium in the YIG system had resulted to achange of structure from cubic to rhombohedral and a fallof the d-spacing indicating the occupancies of aluminiumto tetrahedral and octahedral instead of the larger dodeca-hedral site This created strain and possibly lattice distor-tion and are strongly speculated to have caused the shift ofoperating frequencies Substitution of non magnetic alu-minium had also weakened the super-exchange interactionand thus a fall of real permeability The preparation tech-nique had resulted in single crystal nanoparticles and hadgreatly affected the range of the operating frequencies

Acknowledgment We acknowledged with gratitude thefinancial support by Academy Science of Malaysia (ASM)under the Science Advancement Grant Allocation (SAGA)

References and Notes

1 M Ristic I Nowik S Popovic I Felner and S Music Mate Lett57 2584 (2003)

2 H Zhoa J Zhou Y Bai Z Ejai and L Li J Magn Magn Mater280 208 (2004)

J Nanosci Nanotechnol 11 2652ndash2656 2011 2655

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Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

3 P Vaqueiro and M A Ropez-Quintela Chemical Mater 9 2836(1997)

4 A Leleckaite and A Kareiva Optical Materials 26 123 (2004)5 S Saxena Mater Lett 60 1315 (2006)6 M Rajendran S Deka P A Joy and A K Bhattacharya J Magn

Magn Mater 301 212 (2006)7 A Potdevin G Chadeyron D Boyer and R Mahiou J Non-Cryst

Solids 352 2510 (2006)

8 E P Wohlfarth Ferromagnetic Materials North-Holland PublishingCompany North Holland (1980)

9 E Gamaliy H Štepaacutenkovaacute J Kohout A Snezhko M Kucera andK Nitsch J Magn Magn Mater 242ndash245 766 (2002)

10 W D Kingery H K Bowen and D R Uhlmann Introduction toCeramics John Wiley and Sons New York (1976) p 470

11 N Yahya and G K Hean American J Appl Sci 4 80(2007)

Received 28 June 2009 Accepted 5 October 2009

2656 J Nanosci Nanotechnol 11 2652ndash2656 2011

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RESEARCH

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Yahya et al Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique

The premise of this work focuses on vigorous andsystematic investigation on the garnets having a gen-eral chemical formula of Y3Fe5O12 Aluminum was usedto replace yttrium having stoichiometric composition ofY3minusxAlxFe5O12 with x= 00051015 20 25 and 30by sol gel preparation method The choice of the alu-minum to replace iron for YAG5ndash6 has been done quiteextensively However using aluminum to replace yttriumhas not been reported This was carried out to see whetherthe magnetic properties of the garnet due to the triva-lent Fe ion (Fe3+ that has a moment equivalent to fiveuncompensated spins7 can be retained When the iron iscombined with yttrium and aluminum in a metallic crys-tal the atomic moments are spontaneously held in parallelalignment over regions within each crystallite The regionsin which alignment occurs are called domains which mayextend over many thousands of unit cells8 In consequenceby changing the garnet compositions with the substitutionof aluminum it is possible to alter the structural and hencethe magnetic properties of the garnet system These parti-cles have potential application as magnetic sensor

2 EXPERIMENTAL PROCEDURE

The starting solution is a mixture of iron nitrateFe(NO33 middot9H2O yttrium nitrate Y(NO33 middot6H2O and alu-minum nitrate Al(NO33 middot 9H2O which were dissolved in150 mL of citric acid C6H8O7 middotH2O The mixtures werestirred continuously at about 250 rpm in room tempera-ture until the formation of gel was observed This processwas carried out for one month The gel was dried at 110 Cin an oven to remove the unneeded water The dried pow-der was calcined at 600 C for 3 hours in air and was wetcrushed using a Fritsch Planetary Micro mill for 6 hours toobtain a fine particle powder Subsequently they were sin-tered at 600 C 700 C 800 C and 900 C for 3 hours inair They were characterized by X-ray diffraction (PhilipsXrsquopert PRO PW 3040 PAN Analytical) to confirm the bestgarnet phase Field emission scanning electron microscopy(FESEM SUPRA 35 VP) low resolution transmissionelectron microscope (JOEL JEM CX 200) and high reso-lution transmission electron microscope (FEI Tecnai F20)with 200 kV field emission gun (FEG) were used to studythe morphology and the d-spacing of some of the sam-ples ImageJ software that runs under Linux was used tomeasure the length of the d-spacing A magnetic prop-erty real permeability analysis was carried out using anRF Impedance Analyzer (Agilent 4291B) in the frequencyrange of 10 MHzndash18 GHz

3 RESULTS AND DISCUSSION

X-ray diffraction with CuK radiation K = 089 andwavelength = 154056 Aring was used to determine thecrystal structure of aluminum substituted yttrium iron

garnet samples at different calcining temperatures from600 C to 900 C The unit cell size and geometry wereresolved from the angular positions of the diffractionpeaks whereas arrangement of atoms within the unit cellis associated with the relative intensities of these peaksFrom the X-ray diffraction patterns of the Al-YIG sin-

tered samples at 800 C for 3 hours in air (Fig 1) it wasfound that fully crystalline yttrium iron garnet had beenformed in the Y3Fe5O12 sample The sharp peaks observedindicate high crystallinity of the samples the highest inten-sity that comes from (420) plane from the yttrium irongarnet is 9515 (Fig 1 and Table I) This peak was also pre-viously observed by other researchers6 It is obvious thatthe correct sintering temperature is one of the main factorsaffecting the formation of the garnet phase for all the sam-ples The highest count (4158) for aluminum iron garnetsample was also observed when the sample was sinteredat 800 C Details on the major peaks their intensities andthe d-spacing are given in Table I The substitution of alu-minum to yttrium had resulted in a clear shift of the majorpeak from (420) plane to (104) plane We speculate that itis attributed to the partial occupancy by aluminum ions ofthe tetrahedron and octahedron8ndash10 instead of the dodeca-hedron sites This is due to the fact that aluminum has amuch smaller ionic radius (0530 Aring) compared to that ofyttrium (0892 Aring) The larger dodecahedron sites (240 Aring)are more suitable for the large yttrium ions When morealuminum ions are replace the yttrium they tend to occupythe octahedron (201 Aring) and the tetrahedron (187 Aring) sitesinstead of the dodecahedron site Due to the smaller sizeof the shift from the (420) plane to (104) plane as wellas the observation of two major peaks (Fig 1) located at(420) and (104) planes for sample with x= 15 strengthensthe speculations made with regard to the occupancies ofthese cations It should be noted that there is a sharp fallof d-spacing (Table I) at the major peaks when x = 20which we attributed to the occupancy of more aluminumto the tetrahedron and octahedron sites When lower molefraction of yttrium occupies the dodecahedron site there is

Fig 1 XRD pattern of Al-YIG samples sintered at 800 C

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RESEARCH

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Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

Table I Intensity and 2-theta for Al-YIG samples sintered at 800 C

Mole 2-Theta Intensity d-spacing Av d-spacing hkl

fraction (x) (deg) (au) (Aring) (Aring) (major peak)

00 3234 951500 277 277 42005 3245 695500 276 276 42010 3263 465600 274 274 42015 3270 279600 273 274 42020 3322 330018 270 270 10425 3324 314700 270 270 10430 3330 415800 269 270 104

a shrink of the mentioned site and the total garnet struc-ture A closer look at Figure 1 reveals a slight gradual shiftof the major peak to higher 2-theta at (420) plane Thisindicates that a slight change of the position of some atomsin a systematic manner had caused this effect It couldbe speculated that when more aluminum replaces yttriumtwo major changes might had happened First the decreaseof yttrium from the dodecahedron site had caused a slightshrink to this sub-lattice and secondly the increment ofaluminum at the smaller octahedron and tetrahedron sitesmight have given a slight distortion to the major (420)plane of the lattice The slight move to the higher 2-thetaangle (Fig 1) indicates a smaller cell volume which isin accord with the speculation made Interesting howeveris the stable peak at plane (104) for x = 2025 and 30possibly due to the stable rhombohedron structure formedIt is significant to note that the sol gel technique gaveexcellent results of the Al-YIG samplesFESEM micrographs of the crystalline yttrium iron gar-

net sample sintered at 800 C for 3 hours in air are shownin Figure 2 From the FESEM micrographs in Figure 2 itcan be observed that when more aluminum is substitutingyttrium x = 20 and 25 clear cubic-like structure can beobserved (Fig 2) which we speculated to be single crystalstructure of garnet The average size of the morphology ofthe Al-YIG substitution can be observed in Table IIThe corresponding EDX results of sample Y3Fe5O12

shows that the oxygen iron and yttrium elements arewith atomic percentages of 5521 2577 and 1902respectively (Table II) No impurities were observed dueto the high purity starting materials of the sample compo-sition and stringent control of the preparation proceduresThe atomic of ferum to oxygen is a constant as what

x = 20 x = 25

Fig 2 Field emission scanning electron microscopy for samplesY3minusxAlxFe5O12 where x = 20 and 25 sintered at 800 C

Table II Summary of atomic and grain size for Al-YIG samplessintered at 800 C

Atomic

Mole Oxygen Aluminium Ferum Yttrium Grain sizefraction (x) (K) (K) (L) L (nm)

00 5521 000 2577 1902 82105 5769 202 2939 1090 57810 5528 499 2780 1192 55915 5747 695 2729 829 25220 5930 706 2722 642 46525 5688 898 3213 201 64230 5937 1306 2757 000 553

we expected Compared to oxygen the higher peak oxy-gen in the spectrum indicated more concentration of oxy-gen comparing to the ferum element as in the formulaY3minusxAlxFe5O12 Table II shows the atomic of yttriumversus mole fraction for the Al-YIG samples sintered at800 C which was extracted from the EDX data There isa gradual fall of yttrium and a consistent rise of atomicof yttrium On the other hand since we did not change themole fraction of the ferum and the oxygen of the Al-YIGthere is a constant atomic of both these elementsThe FESEM (Fig 2) images for samples with x = 20

and x = 25 that exhibit a cubic-like single crystal struc-tures had attracted our interest Further analysis was doneusing high resolution transmission electron microscopy(HRTEM) Observing Figure 3 for x = 20 the size of theparticles show an average d-spacing of 366 Aring Extract-ing the data of d-spacing from the XRD data (Fig1)we correspond this to the (012) plane The average par-ticle size of sample with x = 20 and x = 25 is 430 Aringand 465 Aring obtained from HRTEM and FESEM respec-tively The difference between the particle size obtainedfrom those of the HRTEM and FESEM micrographs isjust about 8 On the other hand sample with x = 25showed an average d-spacing of about 273 Aring The aver-age particle size of sample with x = 25 is 563 Aring and642 Aring obtained from HRTEM and FESEM respectivelyThis is about 14 difference obtained between those of theFESEM to the HRTEM micrographs It should be notedthat average d-spacing obtained from the HRTEM image

d-spacing366 Aring(012)

430 Aring

Particle size(average)

d-spacing273 Aring(104)

563 Aring

Particle size(average)

Fig 3 Particle size and d-spacing of samples Y3minusxAlxFe5O12 wherex = 20 and 25 taken by HRTEM

2654 J Nanosci Nanotechnol 11 2652ndash2656 2011

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Yahya et al Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique

X = 25X = 2X = 0

Fig 4 Electron Diffraction of samples Y3minusxAlxFe5O12 where x = 0020 and 25 taken by Transmission Electron Microscope

comparing with that of the XRD data is in good agreementwith about 1 of difference Figure 4 shows the electrondiffraction pattern of the samples with x = 00 20 and25 This result is consistent with the aforementioned factthe formation of single crystal of the samples that wereprepared via sol gel techniqueAn RF Impedance analyzer (Agilent 4291B) measure-

ment was used to study the magnetic properties of alu-minum substituted yttrium iron garnet samples at sinteredat 800 C for 3 hours in air The measurements of the realpermeability as a function of frequency for all the Al-YIGsamples were done at room temperature using toroid shapesamplesThe real permeability (prime) increases monotonically with

frequency for sample Y3Fe5O12 Obvious resonance peakdue to nature resonance phenomena can be observed in thespectrum at about 300 MHz However beyond 300 MHzthe real permeability starts to decrease rapidly Above thispoint the magnetic moments tend to absorb the energyfrom the external wave anticipating occurrence of spinndashspin interactions as well as spin lattice interactions Thehigher magnetic permeability compared to all the othersamples is due to the easy movement of domain walls asa result of the large grain size This is in good agreementwith FESEM results of the samples The substitution ofaluminum to yttrium when x = 05 shows a fall of realpermeability but an increase of resonance frequency Aswe expected the substitution of non magnetic ions suchas aluminum will result in a weakening of super-exchangeinteractions which resulted to the fall of the real perme-ability values For sample Y25Al05Fe5O12 the real perme-ability values prime increases monotonically with frequencyand when resonance occurred at about 300 MHz it tendsto fall abruptly Real permeability falls and resonance fre-quencies are shifted towards higher values for the rest ofthe Al-YIG samples It has to be noted that the resonancefrequencies of samples with mole fraction gt05 cannot beobserved due to the limitation of the Impedance AnalyzerThe extremely high resonance is speculated to be due tothe fact that aluminum ions are occupying the smallertetrahedron and octahedron sub-lattices as mentioned pre-viously (see X-ray results Fig 1) This is speculated toresult a strain and lattice distortion in both the tetrahedronand the octahedron sub-latticesIt is clearly demonstrated that the operating frequency

range strongly depends on the particle size As the particlesize decrease the operating frequency is shifted to higher

Fig 5 Real permeability versus frequency (Hz) for Al-YIG samples

value (Fig 5) This strengthens the speculations made withregard to the occupancies of the aluminum ions Hencethe desired operating frequency range can be achieved bytailoring the size of the particles in the materials due tothe choice of the preparation method namely the solndashgeltechnique Choosing the desired substitution material suchas aluminum to replace yttrium in the YIG samples willresult in high operating frequencies We intend to use thenano-particle as magnetic sensors for deep water oil andgas exploration

4 CONCLUSION

We had successfully prepared single crystal yttrium irongarnet and aluminium-yttrium iron garnet using a sol geltechnique The long stirring time allows the formation ofsingle crystal garnet structure The substitution of alu-minium to yttrium in the YIG system had resulted to achange of structure from cubic to rhombohedral and a fallof the d-spacing indicating the occupancies of aluminiumto tetrahedral and octahedral instead of the larger dodeca-hedral site This created strain and possibly lattice distor-tion and are strongly speculated to have caused the shift ofoperating frequencies Substitution of non magnetic alu-minium had also weakened the super-exchange interactionand thus a fall of real permeability The preparation tech-nique had resulted in single crystal nanoparticles and hadgreatly affected the range of the operating frequencies

Acknowledgment We acknowledged with gratitude thefinancial support by Academy Science of Malaysia (ASM)under the Science Advancement Grant Allocation (SAGA)

References and Notes

1 M Ristic I Nowik S Popovic I Felner and S Music Mate Lett57 2584 (2003)

2 H Zhoa J Zhou Y Bai Z Ejai and L Li J Magn Magn Mater280 208 (2004)

J Nanosci Nanotechnol 11 2652ndash2656 2011 2655

Delivered by Ingenta toDTV - Technical Knowledge Center of Denmark

IP 1923867112Sat 19 Mar 2011 092500

RESEARCH

ARTIC

LE

Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

3 P Vaqueiro and M A Ropez-Quintela Chemical Mater 9 2836(1997)

4 A Leleckaite and A Kareiva Optical Materials 26 123 (2004)5 S Saxena Mater Lett 60 1315 (2006)6 M Rajendran S Deka P A Joy and A K Bhattacharya J Magn

Magn Mater 301 212 (2006)7 A Potdevin G Chadeyron D Boyer and R Mahiou J Non-Cryst

Solids 352 2510 (2006)

8 E P Wohlfarth Ferromagnetic Materials North-Holland PublishingCompany North Holland (1980)

9 E Gamaliy H Štepaacutenkovaacute J Kohout A Snezhko M Kucera andK Nitsch J Magn Magn Mater 242ndash245 766 (2002)

10 W D Kingery H K Bowen and D R Uhlmann Introduction toCeramics John Wiley and Sons New York (1976) p 470

11 N Yahya and G K Hean American J Appl Sci 4 80(2007)

Received 28 June 2009 Accepted 5 October 2009

2656 J Nanosci Nanotechnol 11 2652ndash2656 2011

Delivered by Ingenta toDTV - Technical Knowledge Center of Denmark

IP 1923867112Sat 19 Mar 2011 092500

RESEARCH

ARTIC

LE

Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

Table I Intensity and 2-theta for Al-YIG samples sintered at 800 C

Mole 2-Theta Intensity d-spacing Av d-spacing hkl

fraction (x) (deg) (au) (Aring) (Aring) (major peak)

00 3234 951500 277 277 42005 3245 695500 276 276 42010 3263 465600 274 274 42015 3270 279600 273 274 42020 3322 330018 270 270 10425 3324 314700 270 270 10430 3330 415800 269 270 104

a shrink of the mentioned site and the total garnet struc-ture A closer look at Figure 1 reveals a slight gradual shiftof the major peak to higher 2-theta at (420) plane Thisindicates that a slight change of the position of some atomsin a systematic manner had caused this effect It couldbe speculated that when more aluminum replaces yttriumtwo major changes might had happened First the decreaseof yttrium from the dodecahedron site had caused a slightshrink to this sub-lattice and secondly the increment ofaluminum at the smaller octahedron and tetrahedron sitesmight have given a slight distortion to the major (420)plane of the lattice The slight move to the higher 2-thetaangle (Fig 1) indicates a smaller cell volume which isin accord with the speculation made Interesting howeveris the stable peak at plane (104) for x = 2025 and 30possibly due to the stable rhombohedron structure formedIt is significant to note that the sol gel technique gaveexcellent results of the Al-YIG samplesFESEM micrographs of the crystalline yttrium iron gar-

net sample sintered at 800 C for 3 hours in air are shownin Figure 2 From the FESEM micrographs in Figure 2 itcan be observed that when more aluminum is substitutingyttrium x = 20 and 25 clear cubic-like structure can beobserved (Fig 2) which we speculated to be single crystalstructure of garnet The average size of the morphology ofthe Al-YIG substitution can be observed in Table IIThe corresponding EDX results of sample Y3Fe5O12

shows that the oxygen iron and yttrium elements arewith atomic percentages of 5521 2577 and 1902respectively (Table II) No impurities were observed dueto the high purity starting materials of the sample compo-sition and stringent control of the preparation proceduresThe atomic of ferum to oxygen is a constant as what

x = 20 x = 25

Fig 2 Field emission scanning electron microscopy for samplesY3minusxAlxFe5O12 where x = 20 and 25 sintered at 800 C

Table II Summary of atomic and grain size for Al-YIG samplessintered at 800 C

Atomic

Mole Oxygen Aluminium Ferum Yttrium Grain sizefraction (x) (K) (K) (L) L (nm)

00 5521 000 2577 1902 82105 5769 202 2939 1090 57810 5528 499 2780 1192 55915 5747 695 2729 829 25220 5930 706 2722 642 46525 5688 898 3213 201 64230 5937 1306 2757 000 553

we expected Compared to oxygen the higher peak oxy-gen in the spectrum indicated more concentration of oxy-gen comparing to the ferum element as in the formulaY3minusxAlxFe5O12 Table II shows the atomic of yttriumversus mole fraction for the Al-YIG samples sintered at800 C which was extracted from the EDX data There isa gradual fall of yttrium and a consistent rise of atomicof yttrium On the other hand since we did not change themole fraction of the ferum and the oxygen of the Al-YIGthere is a constant atomic of both these elementsThe FESEM (Fig 2) images for samples with x = 20

and x = 25 that exhibit a cubic-like single crystal struc-tures had attracted our interest Further analysis was doneusing high resolution transmission electron microscopy(HRTEM) Observing Figure 3 for x = 20 the size of theparticles show an average d-spacing of 366 Aring Extract-ing the data of d-spacing from the XRD data (Fig1)we correspond this to the (012) plane The average par-ticle size of sample with x = 20 and x = 25 is 430 Aringand 465 Aring obtained from HRTEM and FESEM respec-tively The difference between the particle size obtainedfrom those of the HRTEM and FESEM micrographs isjust about 8 On the other hand sample with x = 25showed an average d-spacing of about 273 Aring The aver-age particle size of sample with x = 25 is 563 Aring and642 Aring obtained from HRTEM and FESEM respectivelyThis is about 14 difference obtained between those of theFESEM to the HRTEM micrographs It should be notedthat average d-spacing obtained from the HRTEM image

d-spacing366 Aring(012)

430 Aring

Particle size(average)

d-spacing273 Aring(104)

563 Aring

Particle size(average)

Fig 3 Particle size and d-spacing of samples Y3minusxAlxFe5O12 wherex = 20 and 25 taken by HRTEM

2654 J Nanosci Nanotechnol 11 2652ndash2656 2011

Delivered by Ingenta toDTV - Technical Knowledge Center of Denmark

IP 1923867112Sat 19 Mar 2011 092500

RESEARCH

ARTIC

LE

Yahya et al Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique

X = 25X = 2X = 0

Fig 4 Electron Diffraction of samples Y3minusxAlxFe5O12 where x = 0020 and 25 taken by Transmission Electron Microscope

comparing with that of the XRD data is in good agreementwith about 1 of difference Figure 4 shows the electrondiffraction pattern of the samples with x = 00 20 and25 This result is consistent with the aforementioned factthe formation of single crystal of the samples that wereprepared via sol gel techniqueAn RF Impedance analyzer (Agilent 4291B) measure-

ment was used to study the magnetic properties of alu-minum substituted yttrium iron garnet samples at sinteredat 800 C for 3 hours in air The measurements of the realpermeability as a function of frequency for all the Al-YIGsamples were done at room temperature using toroid shapesamplesThe real permeability (prime) increases monotonically with

frequency for sample Y3Fe5O12 Obvious resonance peakdue to nature resonance phenomena can be observed in thespectrum at about 300 MHz However beyond 300 MHzthe real permeability starts to decrease rapidly Above thispoint the magnetic moments tend to absorb the energyfrom the external wave anticipating occurrence of spinndashspin interactions as well as spin lattice interactions Thehigher magnetic permeability compared to all the othersamples is due to the easy movement of domain walls asa result of the large grain size This is in good agreementwith FESEM results of the samples The substitution ofaluminum to yttrium when x = 05 shows a fall of realpermeability but an increase of resonance frequency Aswe expected the substitution of non magnetic ions suchas aluminum will result in a weakening of super-exchangeinteractions which resulted to the fall of the real perme-ability values For sample Y25Al05Fe5O12 the real perme-ability values prime increases monotonically with frequencyand when resonance occurred at about 300 MHz it tendsto fall abruptly Real permeability falls and resonance fre-quencies are shifted towards higher values for the rest ofthe Al-YIG samples It has to be noted that the resonancefrequencies of samples with mole fraction gt05 cannot beobserved due to the limitation of the Impedance AnalyzerThe extremely high resonance is speculated to be due tothe fact that aluminum ions are occupying the smallertetrahedron and octahedron sub-lattices as mentioned pre-viously (see X-ray results Fig 1) This is speculated toresult a strain and lattice distortion in both the tetrahedronand the octahedron sub-latticesIt is clearly demonstrated that the operating frequency

range strongly depends on the particle size As the particlesize decrease the operating frequency is shifted to higher

Fig 5 Real permeability versus frequency (Hz) for Al-YIG samples

value (Fig 5) This strengthens the speculations made withregard to the occupancies of the aluminum ions Hencethe desired operating frequency range can be achieved bytailoring the size of the particles in the materials due tothe choice of the preparation method namely the solndashgeltechnique Choosing the desired substitution material suchas aluminum to replace yttrium in the YIG samples willresult in high operating frequencies We intend to use thenano-particle as magnetic sensors for deep water oil andgas exploration

4 CONCLUSION

We had successfully prepared single crystal yttrium irongarnet and aluminium-yttrium iron garnet using a sol geltechnique The long stirring time allows the formation ofsingle crystal garnet structure The substitution of alu-minium to yttrium in the YIG system had resulted to achange of structure from cubic to rhombohedral and a fallof the d-spacing indicating the occupancies of aluminiumto tetrahedral and octahedral instead of the larger dodeca-hedral site This created strain and possibly lattice distor-tion and are strongly speculated to have caused the shift ofoperating frequencies Substitution of non magnetic alu-minium had also weakened the super-exchange interactionand thus a fall of real permeability The preparation tech-nique had resulted in single crystal nanoparticles and hadgreatly affected the range of the operating frequencies

Acknowledgment We acknowledged with gratitude thefinancial support by Academy Science of Malaysia (ASM)under the Science Advancement Grant Allocation (SAGA)

References and Notes

1 M Ristic I Nowik S Popovic I Felner and S Music Mate Lett57 2584 (2003)

2 H Zhoa J Zhou Y Bai Z Ejai and L Li J Magn Magn Mater280 208 (2004)

J Nanosci Nanotechnol 11 2652ndash2656 2011 2655

Delivered by Ingenta toDTV - Technical Knowledge Center of Denmark

IP 1923867112Sat 19 Mar 2011 092500

RESEARCH

ARTIC

LE

Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

3 P Vaqueiro and M A Ropez-Quintela Chemical Mater 9 2836(1997)

4 A Leleckaite and A Kareiva Optical Materials 26 123 (2004)5 S Saxena Mater Lett 60 1315 (2006)6 M Rajendran S Deka P A Joy and A K Bhattacharya J Magn

Magn Mater 301 212 (2006)7 A Potdevin G Chadeyron D Boyer and R Mahiou J Non-Cryst

Solids 352 2510 (2006)

8 E P Wohlfarth Ferromagnetic Materials North-Holland PublishingCompany North Holland (1980)

9 E Gamaliy H Štepaacutenkovaacute J Kohout A Snezhko M Kucera andK Nitsch J Magn Magn Mater 242ndash245 766 (2002)

10 W D Kingery H K Bowen and D R Uhlmann Introduction toCeramics John Wiley and Sons New York (1976) p 470

11 N Yahya and G K Hean American J Appl Sci 4 80(2007)

Received 28 June 2009 Accepted 5 October 2009

2656 J Nanosci Nanotechnol 11 2652ndash2656 2011

Delivered by Ingenta toDTV - Technical Knowledge Center of Denmark

IP 1923867112Sat 19 Mar 2011 092500

RESEARCH

ARTIC

LE

Yahya et al Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique

X = 25X = 2X = 0

Fig 4 Electron Diffraction of samples Y3minusxAlxFe5O12 where x = 0020 and 25 taken by Transmission Electron Microscope

comparing with that of the XRD data is in good agreementwith about 1 of difference Figure 4 shows the electrondiffraction pattern of the samples with x = 00 20 and25 This result is consistent with the aforementioned factthe formation of single crystal of the samples that wereprepared via sol gel techniqueAn RF Impedance analyzer (Agilent 4291B) measure-

ment was used to study the magnetic properties of alu-minum substituted yttrium iron garnet samples at sinteredat 800 C for 3 hours in air The measurements of the realpermeability as a function of frequency for all the Al-YIGsamples were done at room temperature using toroid shapesamplesThe real permeability (prime) increases monotonically with

frequency for sample Y3Fe5O12 Obvious resonance peakdue to nature resonance phenomena can be observed in thespectrum at about 300 MHz However beyond 300 MHzthe real permeability starts to decrease rapidly Above thispoint the magnetic moments tend to absorb the energyfrom the external wave anticipating occurrence of spinndashspin interactions as well as spin lattice interactions Thehigher magnetic permeability compared to all the othersamples is due to the easy movement of domain walls asa result of the large grain size This is in good agreementwith FESEM results of the samples The substitution ofaluminum to yttrium when x = 05 shows a fall of realpermeability but an increase of resonance frequency Aswe expected the substitution of non magnetic ions suchas aluminum will result in a weakening of super-exchangeinteractions which resulted to the fall of the real perme-ability values For sample Y25Al05Fe5O12 the real perme-ability values prime increases monotonically with frequencyand when resonance occurred at about 300 MHz it tendsto fall abruptly Real permeability falls and resonance fre-quencies are shifted towards higher values for the rest ofthe Al-YIG samples It has to be noted that the resonancefrequencies of samples with mole fraction gt05 cannot beobserved due to the limitation of the Impedance AnalyzerThe extremely high resonance is speculated to be due tothe fact that aluminum ions are occupying the smallertetrahedron and octahedron sub-lattices as mentioned pre-viously (see X-ray results Fig 1) This is speculated toresult a strain and lattice distortion in both the tetrahedronand the octahedron sub-latticesIt is clearly demonstrated that the operating frequency

range strongly depends on the particle size As the particlesize decrease the operating frequency is shifted to higher

Fig 5 Real permeability versus frequency (Hz) for Al-YIG samples

value (Fig 5) This strengthens the speculations made withregard to the occupancies of the aluminum ions Hencethe desired operating frequency range can be achieved bytailoring the size of the particles in the materials due tothe choice of the preparation method namely the solndashgeltechnique Choosing the desired substitution material suchas aluminum to replace yttrium in the YIG samples willresult in high operating frequencies We intend to use thenano-particle as magnetic sensors for deep water oil andgas exploration

4 CONCLUSION

We had successfully prepared single crystal yttrium irongarnet and aluminium-yttrium iron garnet using a sol geltechnique The long stirring time allows the formation ofsingle crystal garnet structure The substitution of alu-minium to yttrium in the YIG system had resulted to achange of structure from cubic to rhombohedral and a fallof the d-spacing indicating the occupancies of aluminiumto tetrahedral and octahedral instead of the larger dodeca-hedral site This created strain and possibly lattice distor-tion and are strongly speculated to have caused the shift ofoperating frequencies Substitution of non magnetic alu-minium had also weakened the super-exchange interactionand thus a fall of real permeability The preparation tech-nique had resulted in single crystal nanoparticles and hadgreatly affected the range of the operating frequencies

Acknowledgment We acknowledged with gratitude thefinancial support by Academy Science of Malaysia (ASM)under the Science Advancement Grant Allocation (SAGA)

References and Notes

1 M Ristic I Nowik S Popovic I Felner and S Music Mate Lett57 2584 (2003)

2 H Zhoa J Zhou Y Bai Z Ejai and L Li J Magn Magn Mater280 208 (2004)

J Nanosci Nanotechnol 11 2652ndash2656 2011 2655

Delivered by Ingenta toDTV - Technical Knowledge Center of Denmark

IP 1923867112Sat 19 Mar 2011 092500

RESEARCH

ARTIC

LE

Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

3 P Vaqueiro and M A Ropez-Quintela Chemical Mater 9 2836(1997)

4 A Leleckaite and A Kareiva Optical Materials 26 123 (2004)5 S Saxena Mater Lett 60 1315 (2006)6 M Rajendran S Deka P A Joy and A K Bhattacharya J Magn

Magn Mater 301 212 (2006)7 A Potdevin G Chadeyron D Boyer and R Mahiou J Non-Cryst

Solids 352 2510 (2006)

8 E P Wohlfarth Ferromagnetic Materials North-Holland PublishingCompany North Holland (1980)

9 E Gamaliy H Štepaacutenkovaacute J Kohout A Snezhko M Kucera andK Nitsch J Magn Magn Mater 242ndash245 766 (2002)

10 W D Kingery H K Bowen and D R Uhlmann Introduction toCeramics John Wiley and Sons New York (1976) p 470

11 N Yahya and G K Hean American J Appl Sci 4 80(2007)

Received 28 June 2009 Accepted 5 October 2009

2656 J Nanosci Nanotechnol 11 2652ndash2656 2011

Delivered by Ingenta toDTV - Technical Knowledge Center of Denmark

IP 1923867112Sat 19 Mar 2011 092500

RESEARCH

ARTIC

LE

Aluminium Substituted Yttrium-Iron Garnet Nanoparticles Prepared Using Sol Gel Technique Yahya et al

3 P Vaqueiro and M A Ropez-Quintela Chemical Mater 9 2836(1997)

4 A Leleckaite and A Kareiva Optical Materials 26 123 (2004)5 S Saxena Mater Lett 60 1315 (2006)6 M Rajendran S Deka P A Joy and A K Bhattacharya J Magn

Magn Mater 301 212 (2006)7 A Potdevin G Chadeyron D Boyer and R Mahiou J Non-Cryst

Solids 352 2510 (2006)

8 E P Wohlfarth Ferromagnetic Materials North-Holland PublishingCompany North Holland (1980)

9 E Gamaliy H Štepaacutenkovaacute J Kohout A Snezhko M Kucera andK Nitsch J Magn Magn Mater 242ndash245 766 (2002)

10 W D Kingery H K Bowen and D R Uhlmann Introduction toCeramics John Wiley and Sons New York (1976) p 470

11 N Yahya and G K Hean American J Appl Sci 4 80(2007)

Received 28 June 2009 Accepted 5 October 2009

2656 J Nanosci Nanotechnol 11 2652ndash2656 2011