Investigation of site preference of Zn doped Ba3Co2− x Zn x Fe24O41 by MössbauerspectroscopyJung Tae Lim and Chul Sung Kim Citation: Journal of Applied Physics 115, 17D706 (2014); doi: 10.1063/1.4861676 View online: http://dx.doi.org/10.1063/1.4861676 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/115/17?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The crystal structure and magnetic properties of Ba2−xSrxCo2Fe12O22 J. Appl. Phys. 115, 17A523 (2014); 10.1063/1.4866892 Magnetic properties of Zn doped Co2Y hexaferrite by using high-field Mössbauer spectroscopy J. Appl. Phys. 115, 17A516 (2014); 10.1063/1.4865879 Magnetic properties of Ni substituted Y-type barium ferrite J. Appl. Phys. 115, 17A509 (2014); 10.1063/1.4860939 Investigation of magnetic properties of non-magnetic ion (Al, Ga, In) doped Ba2Mg0.5Co1.5Fe12O22 J. Appl. Phys. 111, 07A518 (2012); 10.1063/1.3679023 Mössbauer studies of BaFe 11.9 Mn 0.1 O 19 by a sol–gel method J. Appl. Phys. 87, 6244 (2000); 10.1063/1.372668

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Investigation of site preference of Zn doped Ba3Co22xZnxFe24O41 byM€ossbauer spectroscopy

Jung Tae Lim and Chul Sung Kima)

Department of Physics, Kookmin University, Seoul 136-702, South Korea

(Presented 7 November 2013; received 23 September 2013; accepted 16 October 2013; published

online 29 January 2014)

The polycrystalline Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0) samples were prepared by using

solid-state-reaction method. The crystal structures and magnetic properties of samples were

investigated with x-ray diffractometer, vibrating sample magnetometer, and M€ossbauer spectroscopy.

The crystal structure of Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0) samples was determined to be a

hexagonal structure with P63/mmc space group at 295 K, and the saturation magnetization (Ms) of

Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0) samples were found to be Ms ¼ 50.9, 53.1, 55.0 emu/g,

respectively. From the temperature dependence of magnetization curves under 100 Oe between 4.2

and 740 K, we were able to observe the spin transition, and both spin transition temperature (Ts) and

Curie temperature (TC) decrease with increasing Zn concentration. M€ossbauer spectra of all samples

were obtained and analyzed at various temperatures ranging from 4.2 to 295 K. With ten-sextets for

Fe sites corresponding to the Z-type hexagonal crystallographic sites, all spectra below TC were fitted

by least-square method. In addition, from the site occupation numbers of Fe, calculated from the

relative areas fitted to the M€ossbauer spectra, we find that Zn ions preferentially occupy the tetrahedral

sublattices of down sites. VC 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4861676]

I. INTRODUCTION

Z-type hexaferrite, Ba3Me2Fe24O41 (Me¼Zn, Fe, Co,

Mg, Mn) with non-collinear magnetic structures has been

studied for magnetoelectric (ME) effect based on the

spin-current model. Also, Z-type hexaferrite has highest

magnetic planar anisotropy than other ferrite family have

and has been extensively studied for high-frequency applica-

tions such as microwave device and electromagnetic (EM)

wave absorber materials. Their properties, such as perme-

ability and permittivity in high-frequency, ME effect depend

on their saturation magnetization (Ms) and magnetic anisot-

ropy, and found to be strongly affected by the distribution of

transition metallic ions at the sites for Z-type hexaferrite.

However, the nature of the magnetic properties on the each

interstitial site in Z-type hexaferrite has not been studied

compared to other hexaferrite, although the site occupancy

of transition metallic ions in Z-type hexaferrite is important

to understand the origin of the magnetic properties.

In general, Z-type hexaferrite has complex spin reorien-

tation. As the temperature increases up to 230 K, the anisot-

ropy changes from conical to planar and becomes uniaxial

for temperature above 500 K. The unit cell of the Z-type hex-

aferrite consists of four S-blocks, two R-blocks, and two

T-blocks. There are ten different interstitial sites for Fe ions,

such as six octahedral sites, three tetrahedral sites, and five-

fold site, as shown in Table I.1–6

In this paper, we have studied the magnetic properties of

Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.5) using XRD, VSM,

and M€ossbauer spectrometer. Especially, M€ossbauer

spectroscopy can provide the detailed information on each

site, site occupancy, and hyperfine distribution.

II. EXPERIMENT

The polycrystalline samples of Ba3Co2�xZnxFe24O41

(x¼ 0.0, 0.5, 1.0) were synthesized by using the standard ce-

ramic method. The mixture of high-purity BaCO3 (99.98%),

CoO (99.99%), ZnO (99.999%), and a-Fe2O3 (99.9995%)

powders in the appropriate stoichiometric ratio for Z-type

hexaferrite were ground and calcined at 1000 �C for 10 h in

air. The calcined samples were ground and pressed into a cy-

lindrical pellet, and sintered again at 1200 �C for 10 h in air.

Finally, to obtain good homogeneity, the sintered samples

were annealed at 1250 �C for 10 h. The crystal structure of

samples was characterized by using XRD (Philips X’Pert

PW1830) with Cu-Ka (k¼ 1.5406 A) radiation. The magnet-

ization measurement was performed with VSM (Lake Shore

7300) at various temperatures. Also, M€ossbauer spectra were

TABLE I. Coordination, block location, number of ions, and spin direction

for each sublattice in Z-type hexaferrite.

Site Coordination Block Number of ions Spin Set sublattice

4fIV Tetrahedral S 2 Down A

4fIV* Tetrahedral T 2 Down B

12kVI* Octahedral T-S 6 Up C

4fVI* Octahedral S 2 Up D

4eIV Tetrahedral S 2 Down

12kVI Octahedral R-S 6 Up E

2dV Fivefold R 1 Up

F

2aVI Octahedral T 1 Up

4fVI Octahedral R 2 Down

4eVI Octahedral T 2 Downa)Author to whom correspondence should be addressed. Electronic mail:

cskim@kookmin.ac.kr. FAX: þ82-2-910-5170.

0021-8979/2014/115(17)/17D706/3/$30.00 VC 2014 AIP Publishing LLC115, 17D706-1

JOURNAL OF APPLIED PHYSICS 115, 17D706 (2014)

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recorded using a conventional spectrometer. The spectrome-

ter calibration was performed using an a-Fe foil with a 57Co

source in a rhodium matrix.

III. RESULTS AND DISCUSSION

The XRD patterns of Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5,

1.0) were measured at 295 K and analyzed by Rietveld

refinement technique as shown in Fig. 1. From the refined

XRD patterns, samples were found to be single-phased with

Bragg factor (RB) and structure factor (RF) less than 5%, and

the crystalline structures were determined to be hexagonal

with space group P63/mmc. Also, Fe, Co, and Zn ions were

found to be located at ten crystallographic sites of 4fIV, 4fIV*,

12kVI*, 4fVI

*, 4eIV, 12kVI, 2dV, 2aVI, 4fVI, and 4eVI. The lattice

constants a0, c0 and unit cell volume (Vu) of samples increase

with increasing Zn contents, because the locations of Fe3þ ions

changed from tetrahedral to octahedral sites. Also, the XRD

density of samples increases with increasing Zn substitution.

Fig. 2(a) shows the magnetic hysteresis curves of

Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0) under 10 kOe at

295 K, indicating the ferrimagnetic behavior. With increas-

ing Zn ions substitution, the saturation magnetization (Ms)

of Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0) decreases, since

non-magnetic Zn ions reduce the magnetic moment of the

substituted sites. Therefore, we expect that Zn ions preferen-

tially occupy the 4eIV, 4fIV, and 4fIV* with down-spin site.

Fig. 2(b) shows the temperature dependence of the zero-

field-cooled (ZFC) magnetization curves under the applied

field of 100 Oe between 90 and 740 K. All the samples have

four spin structures, and showed the spin transitions from

conical, perpendicular to the c-axis, to planar spin structure

around 200 K (TS1), from planar to uniaxial spin structure

around 480 K (TS2), and from uniaxial to paramagnetic spin

structure around 680 K. TS1, TS2, and TC of samples decrease

with increasing Zn ions concentration. We expect that the

decreases of TS1 and TS2 are due to the fact that Zn ions do

not have magnetic planar anisotropy, and the decrease of TC

is due to weak super-exchange interaction.1,7–9

In order to investigate the cation distribution and hyper-

fine interaction, the M€ossbauer spectra were obtained at

295 K and fitted with the subspectra as in Fig. 3. The

FIG. 1. XRD patterns of Z-type Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0).

The solid circle represents the observed pattern; the solid lines represent cal-

culated and difference obs-cal patterns. The tick markers correspond to the

position of the allowed Bragg reflections.

FIG. 2. (a) The applied-field dependence of the magnetization curve of

Ba3Co2�xZnxFe24O41 (x ¼ 0.0, 0.5, 1.0) up to 10 kOe at room temperatures.

(b) The temperature dependence of the ZFC magnetization curves under

100 Oe between 90 and 740 K.

FIG. 3. M€ossbauer spectra of Ba3Co2�xZnxFe24O41 (x ¼ 0.0, 0.5, 1.0) at

295 K.

17D706-2 J. T. Lim and C. S. Kim J. Appl. Phys. 115, 17D706 (2014)

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resulting M€ossbauer parameters are listed in Table II. The

M€ossbauer spectra of all samples show a superposition of

ten-sextets for Fe sites corresponding to the Z-type hexago-

nal crystallography sites. Therefore, all spectra were least-

squares fitted with six distinguishable sites, corresponding to

A (4fIV), B (4fIV*), C (12kVI

*), D (4fVI*, 4eIV), E (12kVI), and

F (2dV, 2aVI, 4fVI, and 4eVI). The relative magnitude of

hyperfine field (Hhf) between the sublattices were determined

to be the value of Fermi current field, and the size of the

magnetic tetrahedral site becomes smaller with increasing

Zn concentration. The analysis of M€ossbauer spectra shows

that the average value of hyperfine field hHhfi decreases with

Zn substitution, and the value of isomer shift hdi of the each

subspectra in the compound indicates that the iron ions have

Fe3þ high spin state.10

As shown in Fig. 4, the site occupation numbers of Fe

(NFe(i)) were calculated from the relative areas (S(i) for

i¼ 1-6) fitted to the M€ossbauer spectra. The occupation

numbers of iron ions, NFe(i) at the ith site can be determined

as following:11,12

NFeðiÞ ¼ CFeSðiÞ

X6

i¼1

SðiÞ;

where S(i) is the relative area of each site and CFe is the com-

positions of Fe ions in chemical formula. As a result, the

occupation numbers of down-spin sites decrease with

increasing non-magnetic Zn ions contents. Therefore, Zn

ions preferentially occupy the tetrahedral sublattices, leading

to increase in MS.

IV. CONCLUSIONS

In conclusion, we have studied the physical properties

of Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0) by using XRD,

VSM, and M€ossbauer spectrometer. The crystal structure of

Ba3Co2�xZnxFe24O41 (x¼ 0.0, 0.5, 1.0) samples was deter-

mined to be a hexagonal structure with P63/mmc space

group, and the unit cell volume (Vu) of the samples was

increasing with Zn ion concentration. The temperature-

dependent magnetization curves measured under 100 Oe

between 90 and 740 K show the spin transition effect in all

the samples. The spin transition temperature (TS1, TS2) and

Curie temperature (TC) decrease with increasing Zn ion con-

centration. From the M€ossbauer spectra, the average value of

d obtained from each subspectra of all samples indicates that

the Fe ions are typical Fe3þ. Also, the occupation numbers

of down-spin site decrease with increasing non-magnetic Zn

ions contents, indicating Zn ions preferentially occupy the

tetrahedral sublattices with increase in MS.

ACKNOWLEDGMENTS

This work was supported by Mid-career Researcher

Program through the National Research Foundation of Korea

(NRF) grant funded by the Ministry of Education, Science

and Technology (MEST) (No. 2013-000671).

1Y. Kitagawa et al., Nature Mater. 9, 797 (2010).2Y. Takada et al., J. Appl. Phys. 100, 043904 (2006).3R. C. Pullar and A. K. Bhattacharya, Mater. Res. Bull. 36, 1531 (2001).4T. Tachibana et al., J. Magn. Magn. Mater. 262, 248 (2003).5S. H. Chun et al., Phys. Rev. Lett. 108, 177201 (2012).6K. Ebnabbasi and C. Vittoria, Phys. Rev. B 86, 024430 (2012).7M. Soda et al., Phys. Rev. Lett. 106, 087201 (2011).8M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006).9A. Collomb, M. A. Hadj Farhat, and J. C. Joubert, Mater. Res. Bull. 24,

453 (1989).10J. T. Lim, C. M. Kim, B. W. Lee, and C. S. Kim, J. Appl. Phys. 111,

07A518 (2012).11Z. W. Li, C. K. Ong, Z. Yang, F. L. Wei, X. Z. Zhou, J. H. Zhao, and

A. H. Morrish, Phys. Rev. B 62, 6530 (2000).12M. H. Won and C. S. Kim, J. Appl. Phys. 113, 17D906 (2013).

TABLE II. M€ossbauer hyperfine parameters of Ba3Co2�xZnxFe24O41 at

295 K.

Site

X A B C D E F

0.0 Hhf (kOe) 513.15 493.41 479.76 454.81 421.37 391.09

d (mm/s) 0.26 0.21 0.17 0.31 0.22 0.22

0.5 Hhf (kOe) 511.83 494.52 478.51 451.54 419.99 387.99

d (mm/s) 0.26 0.25 0.17 0.30 0.23 0.23

1.0 Hhf (kOe) 496.53 478.14 460.19 433.78 400.14 376.48

d (mm/s) 0.27 0.21 0.17 0.27 0.22 0.22

FIG. 4. The site occupation numbers of Fe3þ in Ba3Co2�xZnxFe24O41

(x¼ 0.0, 0.5, 1.0).

17D706-3 J. T. Lim and C. S. Kim J. Appl. Phys. 115, 17D706 (2014)

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