RECENT RESEARCH AND DEVELOPMENTON MATERIALS SCIENCE IN JAP ANt

Y. Hamaguchr

ABSTRACTRECENT RESEARCH AND DEVELOPMENT ON MATERIALS SCIENCE IN JAPAN. In Japan the new five

years project based on the Basic Plan for Science and Technology decided in the government has been started from 1996. The targetof this project is to develop the new idea and technology cooperated with universities, governmental institutes and industrialinstitutions supported by the much amount of budget. In this paper the properties and structures of new kind of superconductingoxide and giant magnetoresistant materials mainly obtained in Japan have been presented.

INTRODUCTION Since the field of materials science is toowide to talk all, I will select to two topics relatedto the strongly correlated electron system.After the second world war, Japanese

industries introduced the new basic technologyfrom Europe and USA and improved bythemselves, and academic site of Japan learned toomuch on the advanced scientific knowledge. Bythis way the economical situation improved andgrown up too much. But now such situation couldnot be allowed from many points of view. In 1996Japanese government decided a plan to expensemuch amount of budget for the development ofnew science and technology by ourself. The planinclude the investment of total 17 trillion yenduring five years and construct the new system andorganizations to conducting the several newprojects. In 1997 the total butget for this plan is 3trillion yen[l]. To conducting the new project thecooperative research with industry, university andgovernmental institute is encouraged. In the fieldof materials science new organizations such asInternational Superconductivity Center, JointResearch Center for Atom Technology and Multicore project on High Tc superconductor et al havebeen supported by Ministry of Education, Scienceand Culture (MONBUSYO), New Energy andIndustrial Technology Development Organization.(NEDO) and ScIence and Technology Agency(STA). In the industries new kinds of materialssuch as NEOMAX(hard magnet), FINEMET(softmagnet) have been developed and many academicsites followed to make clear the mechanism ofthem. In the field of practical application of highTc materials, one of them is the development ofleading wire introduced the high current intosuperconducting coil, which has beencommercialized. Using this coil thestiperconducting magnet without liquid He hasbeen developed. The second one is thedevelopment of superconducting wire usingBi2223. Several companies cooperate each otherand with governmental institute succeeded toproduce 50m wire operated at liquid nitrogen

temperature.

COPPER OXIDE WITH SPIN-1/2 HEISEN-BERG LADDER

In 10 years after the discover of high Tcsuperconducting materials, many kinds of newmaterials having the superconducting propertyhave been found and detailed investigation on thephysical properties of those materials has beenmeasured to make clear the origin of thesuperconductivity. Almost all of them consist withthe stacking of Cu-O layer which carry poles orelectrons through it. Several years ago Dgotto et of[2] and Rice et of [3] predicted that copper oxidewith spin-l/2 Heisenberg ladders may show thesuperconductivity by the 'd-wave pairing of holecarriers. Many attempt to find the materials havingthe superconductivity has been started and Prof. M6ri's group in ISSP Tokyo Univ. found that thecompounds made by Prof. Akimitsu's group inJapan[4] showed the superconductivity under thehigh pressure[5]. The materials showing thesuperconductivity is SrI4.xC~CU24041+y which ismade under the high temperature and highpressure. This materials show the superconductingproperty in a very small x-range and pressure. FigI shows the temperature dependence of electricalresistivity at ambient pressure. Up to x=13.0 itshows the semiconductive behavior and x==13.5and 13.6 there is a hump near 100 K.Fig 2 shows the pressure dependence of electricalresistivity on SrO4Ca136Cu24041+Y specimen. Theelectrical resistivity decrease with increasing thepressure and at 3GPa it becomes metallic andshows the superconducting behavior below about8K. With more increase of pressure the electricalresistivity decreases but Tc also decrease and at6GPa the resistivity at 4K still remain finitely.

The temperature dependence of electricalresistivity on more Sr concentrated specimen made

I Presented at The Materials Science Scientific Meeting 1997

2 JAERI -Japan --11

Prosidin Pertemuan Ilmiah SainsMateri 1997 ISSN 1410 -2897

by Dr. Cava, Sr4Ca10C UZ4O41+Y, under the pressureis shown in Fig 3[6].

Fig. 3 Temperature and pressure dependence elec-trical resistivity in SrsCaloCu24041+y [6J.Fig. Temperature dependence of electrical receptivity

in Srl-xCaxCu24041-y, nearx=13.6.[6]With increasing the pressure resistivity

decrease but still show the semiconductivebehavior. Fig 4 shows the pressure dependence ofTc on several kinds of high Tc superconductor. Asshown in the figure the range of pressure to showthe superconductivity in SrO4Cal36CU24041 is verynarrow and too much different with othermaterials.

(8)

'8"6cq.

0 100 150 200 250 300/All: (KJ

0.81 ;(b) Sr~.Ca Cu..O'L" :

50

,..

i 4.5~~-

_O.t;

Ba': 0..~Q,

0.26.0GPa..

..Lj... .0 10 20 30 40 50

1&Jt: (K)

M9~ (a), (b) Sro.Cal,.SCU2tOtltlQJittJtQJH:I), 411t~ftIS). Fig. 4. Pressure dependence ofTc in several super-

conductive oxides. [6]

Fig. 2 Temperature and pressure dependence ofelectrical resistivity (a), (b) in SrO.4Ca13.6

CU24041+y [5]

The detailed crystallographic structure ofSrO4CaI36CU24+yO41+Z at ambient temperature and

pressure has been determined by Dr. Izumi's group

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3(JPa...,

Pros;di~ Pertemuan//m;ah Sa;ns Mater; 1997 /SSN!4/0 -2897

The modulated structure along [100] and [010]directions is shown in Fig. 7.

in NIRIM, Japan by using a Rietveld-refinementprogram, PREMOS, for the powder sample[7]. Theschematic draw of this structure is shown in Fig 5.

Fig. 5. Crystal structure ofCaI4-xSrxCu24+yO41+zviewed in perspective along the [001]direction. [7]

This oxide is a kind of composite crystalconsisting of two interpenetrating sub-systems; (a)[(Ca,8r)2Cu2O3]'" containing alkaline-earth metalsand spin-V2 Heisenberg two-leg ladders and (b)one.dimensional [CuOJ", chains of CuO4 squaresharing two opposite edges. Orthorhombic oxidesMI4CU24+yO41+Z are composite crystal where acouple of incommensurate subsystems alternatewith each other along the a axis. The c dimensionof two subsystem is different, which leads to theabsence of a period along the [001] direction. Tomake the refinement on the incommensuratesystem the superspace group must he introduced.Using the superspace group F222(lIy ) they madethe refinement and got the good r~sult ofR,.p=6.34% for neutron diffraction data (Fig 6).

Fig. 7 Modulated structure ofCaI3.6SrO.4 CU23.983040.965 projected (a) along [100] for an x rangeof 0.273--.0..727 and (b) along [010] for a y rangeof -0.05--.0.4. The unit cells of the twosubstructure are plotted at the bottoms.[7]

This study has clarified the complexmodulated structure of the composite crystalSrO4Ca136Cu23983040965 and the influence of Casubstitution upon the Cu-O bond lengths and thecoordination number of CuI. Its pressure~inducedstructure change at superconducting stage must beinvestigated to understand the role of highpressure and crystallographic structure in thesuperconductivity .

MAGNETORESIST ANCE MA TE-GIANTRIALS

Magnetoresistance effect means thephenomena that the electrical resistvity has beenchanged with the direction and strength of appliedmagnetic field. In the usual ferromagnetic materialsthe ratio of change is several %. This effect hasbeen applied to the reading head of magneticrecording tape as MR head. In 1988 Baibich et offound the giant magnetoresistance, which is oneorder larger than that of ferromagnetic materialsand isotropic, in Fe/Cr multi-layer materials[8]. Inthis m:1terials Cr seems to be nonmagnetic and themagnetic moment of Fe layers coupled anti-

Fig. 6 Rietveld-refinement patterns for the (a) neutronand (b) X-ray diffraction data ofCaI3.6SrO.4Cu23.983040.96S. [7]

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ferromagnetically. In this case magnetoresistancehas bean defmed as MR={PAF -PF)/pF, where PFand PAF are the electrical resistivity with andwithout applied magnetic field. When applied themagnetic field parallel to the magnetic moment ofFe coupling between layers change to ferro-magnetic and electrical resistivity decrease toomuch. The reason of this phenomena has beeninterpreted as the difference of potential applied to+ and -electrons in Fe, which behave the differentscattering behavior at the boundary of Fe and Cr(Fig 8). after the discovery of this phenomenamuch amount of works have been made even inJapan not only from the academic point of view butalso to search the possibility to apply the MR head.One of them is the development of spin valve headshown in Fig. 9.

electron system. Besides this in the (La,Sr)-Mn-Osystem colossal magnetoresistance effect has beenobserved. The homologous series of crys-tallographic structure exist in the perovskite typetransition metal oxides, the chemical formula ofwhich is «R,A)I+nMnO3n+I)' where R is trivalentrear earth element, A is divalent alcaline-earthelement and M is transition metal element. Thehigh Tc oxide (La,Sr)2CuO4 belong to n=l series.The n=(X) correspond to pure perovskite structure.The crystallographic structure of this series isshown in Fig. 10[9].

H

~

B

IT

2u..;1 Fig. ) 0: Crystal structures of layered perovskite-type

Mn oxides.(AI

LaMnO3 is cubic perovskite insulator andbelow 150K it transforms to orthorombic andbecome antiferromagnetic due to the ]- T effectcombined with orbital ordering. The maggneticstructure is so called A~type, which is ferro-coupling in ab plane and anti ferro-coupling in c-direction. The phase diagram of (La,Sr)MnO4 isshown in Fig. 11.

Fig.8: Energy levels of Fe/Cr multi-layer. [1 1)

8ft};,:, (!):*..,.1E',MWft

Mr. """"",7~. f'".".8" ,W~1It~~., M..~~., (c)1It~

Fig.9: Schematic figure of the principle of operation onspin valve head. (a) low resistant stage (b) highresistant stage and (c) curve of resistance-magnetic field. [12]

Recently many kinds of perovskite Mnoxides are in limelight on the stage of materialsscience as the 'Colossal Magnetoresistance'materials. The research on the perovskite Mnoxides has been started in 1950 and muchinformation on the crystallographic, magneticstructUre and theoretical interpretations have beenmade. However using the new techniques ofsample preparation and measurement of physicalproperties developed in the study on the high Tcsuperconduction materials it becomes clear that thisoxides are the other examples of highly correlated

.58La,-,sr,MnO. "'>C'ffflim.T.. T". T.11-':h~hN:~.",-. ~.It.. a:&-m"8.II:~~ l-. PI. PM. AFI. Fl. FM .1-':tt~h~.",-".I*m. ~.",-".m. N:~.tlYf*m. ~.tl".I*m. ~.M;;...mt-.b"t.

Fig. Phase diagram of Lal-xSrxMn 03, TN, TCand TS are the transition temperature of anti-ferromagnetic, ferromagnetic and structuralphase transition. PI, PM" AFI, FI and FMcorrespond to paramagnetic insulator, para-magnetic metal, antiferromagnetic insulator,ferromagnetic metal and ferromagnetic insu-!~t~r each other. [13]

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As shown in the figure with increase ofSr it change to ferromagnetic insulator and finallybecomes to ferromagoetic metal. By thereplacement of LaJ+ with x of Sr+, x of Mn4+ hasbeen produced and introduce the hole into eg band.Due to the movement of holes it becomes

ferromagnetic by the double exchange mechanismand with increase of x, it shows the metal-insulatortransition. Near the metal. insulator transitionregion, for example L30SSrO2MnO4, it shows the'colossal magnetoresistance effect' slightly aboveTc as shown in Fig 12.

In the n=1 Mn oxide, (Lal-xSrx)2CuO4,there is no indication of metal-insulator transitionup to x = 0.7 and they are insulator. In the n=2 Mn

oxide, L~-2XSrl+2xMn2O7 , it was found that forw=O.4 oxIde the paramagnetic insulator to

ferromagnetic metal transition exist at 126K. Theprecise measurements on the electrical resistivityand magnetization have been made by Prof.Tokura's group in Tokyo Univ. and JRCAT usingsingle crystal[IO]. The 'colossal magnetoresistance'has been observed in x=O.3 oxide. Fig 14 shows the

temperature dependence of inverse magnetizationand electrical resistivity both in ab plane and c-direction.

"6~~

;

Fig.14: The temperature dependence of inverse magne-tization(upper) and electrical resistivity in andbetween ab plane for La2-2xSrl+2xMn207

(x=3) single crystal. [14]

..'KI",. "',-$..MnO,.a"..+"t"'...~.".*~#ft

w,-o". (b) ,-0 "'. {d,-Oa8~lt. -(.(,')-.(0)]/.{.)"t'~.3IL"...KJt(MR ).,.h"t.

Fig 12: Temperature dependence of electrical resisti-

vity ofLal-xSrxMnO3 under the mgnetic-fields. [13]

Schematic drawing of double exchangemechanism and origin of colossal magneto-resistance is shown in Fig. 13.

Fig. 3: Schematic diagram of appearance ferromagne-tic metal phase and GMR due to the double

exchangemechanism. [13]

In ab plane electrical resistivity showedthe maximum at about 270K(~ mIX)' below this itshowed the metallic behavior and from about lOOKshowed more large decreasing rate. In the c-direction up to lOOK it showed the semiconductivebehavior, below lOOK (J'c mIX) it deceased veryquickly and showed the metallic behavior. Bothtemperature correspond to the anomalies in thecurve of inverse magnetization. The magnetic fielddependence of electrical resistivity in bothdirection are shown in Fig 15. In c-direction atlOOK this materials showed very largemagnetoresistanec of p(O kOe)/p (50 kOe) ::: 104.Schematic interpretation of this 'colossalmagnetoresistance effect' is shown in Fig 16. In then=2 perovskite structure, a coupe of magneticMnO2 plane is separated with nonmagnetic(La,Sr)P2 plane. It is something like microscopic

multilayer system.Above T"bmax ab plane is paramagnetic and

in both directions they are insulator. Below Tabmaxab plane coupled ferromagnetically by the double

15

Prosidin Pertemuan //miah Sains Materi 1997 ISSN 1410 -2897

exchange mechanism and metallic, but betweenab planes no correlation exist which means con-ductive behavior is semiconductive. Below about90K the correlation between ab plane is developedand system become 3 dimensional ferromagnet.

with the idea that by the addition of C or B intoR2Fel7 to expand the Fe-Fe distance in dumbbellsite.

After tried to make many kinds of samplewith combination of several parameters for themaking procedure, he succeeded to found the bestone. However the main part contributed to the bigmagnetic energy preduct of NEOMAX is notNe2Fel7 but Ne2Fel4B and Fe-Fe distance in thiscompound is smaller than that of Ne2Fe17, but dueto the 'effective filling' effect theoreticallypredicted by Prof. Kanamori.

In the case of the development of 'GMR'or 'CMR', sample preparation techniques playaimportant role, such as multi-layer samples and Mnoxides.Conclusively the cooperative development oftheory, sample preparation and characterizationtechniques, good idea, laborious works and goodluck is important for the materials science.

REFERENCES

Fig. 15:Temperature dependence of electrical resistivityof La2-2xSrl+2xMn207 (x=O.3) single crystalunder the magnetic fields. [14]

Ever at 4K MR in c-direction is fairly large as240%, which can be explain by assuming theconstruction of micro-magnetic domain between c-direction without magnetic field and by applyingthe magnetic field all domain align parallel to c-direction.

SUMMARY

The success of new kind of good qualitymaterials is effective for the innovation oftechnology in many field. However for thedevelopment of new materials not only muchamount of laborious works but also a good luck arenecessary. In the case of ladder-type super-conductor, Dr. Cava in Bell Lab. succeeded tomake the sample having the similar compositionwith that made by Prof. Akimitsu's group, but theratio of Sr/Ca is different. Even at high pressurehis sample did not show the superconductivity.Prof. Akimitsu's group tried to make many kinds ofsample, modified the Sr/Ca ratio and succeeded tofound the superconducting materials in the narrowcomposition range and pressure. For the guide ofthis works the theoretical prediction played a veryimportant role. In the case of the development ofNEOMAX, Dr. Sagawa started his research works

[1] Tsuyoshi Masumoto: Materia Japan36(1997)65. (in Japanese)

[2] Dagotto E., Riera J. and Scalapino D.: Phys.Rev. B45(1992) 5744.

[3] Rice T.M., Copalan S. and Sigrist M.:Europhys. Lett. 23(1993) 445.

[4] Uehara M., Ogawa M. and Akimitsu J.:Physica C 255(1995) 193.

[5] Uehara M., Nagata T., Akimitsu J., TakahashiH., Mari M. and Kinoshita K.: J.Phys. Soc.Jpn. 65(1996) 2764.

[6] Mari N., Takahashi H. and Nakanishi T.: SolidState Physics(Kotai Butsuri) 3 1(1996) 797.(inJapanese)

[7] Ohta T., Izumi F., Onodera M., Isobe M.,Takayama E.-Muromachi and Hewat A. W.:J.Phys. Spe. Jpn. 66(1997) No. 10. in press.

[8] Baibich M.N., Broto J.M., Fert A., NguyenVan Dau F., Petroff F., Etienne P., Creuzet G.,

[9] Friederich A. and Chazelas J.: Phys. Rev. Lett.61(1988) 2472.

[10] Asamitsu A., Okimoto Y. and Tokura Y.:Solid State Physics(Kotai Butsuri)32(1997)258.and reference of this paper.(inJapanese)

[1 I] Moritomo Y., Asamitsu A., Kuwahara H. andTokura Y.: Nature 380(1996) 141.

[12] Maekawa S.: Solid State Physics (KotaiButsuri) 32(1997) 203. (in Japanese)

[13] Nakada M and Yamada K.: Solid StatePhysics(Kotai Butsuri) 32( 1997) 242. (inJapanese)

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Prosidin.l! Pertemuan I/miah Sains Materi 1997 ISSN1410 -2827

[14] Asamitsu A., Okimoto Y. and Tokura Y.:Solid State Physics(Kotai Butsuri) 32(1997)258.(in Japanese)

[15] Kimura T. and Tokura Yo: Solid StatePhysics(Kotai Butsuri) 32(1997) 298. (inJapanese)

17.