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MAGNETIC PROPERTIES OF Cu1/2In1/2Cr2S4 AND SOME RELATED COMPOUNDS
R. Plumier, F. Lotgering, R. van Stapele
To cite this version:
R. Plumier, F. Lotgering, R. van Stapele. MAGNETIC PROPERTIES OF Cu1/2In1/2Cr2S4 AND SOME RELATED COMPOUNDS. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-324-C1-325.
�10.1051/jphyscol:19711107�. �jpa-00213922�
JOURNAL DE PHYSIQUE Colloque C I , suppl&ment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C - 1 324
MAGNETIC PROPERTIES OF C U , , ~ I ~ , , ~ C ~ ~ S ~ AND SOME RELATED COMPOUNDS
by R. PLUMIER and F. K. LOTGERING (*), R. P. van STAPELE (*) Centre #Etudes NuclCaires de Saclay, 91, Gif-sur-Yvette, France
Resume. - Les proprietes magnktiques des composes spinelles MllzInllzCrzX4 oh M = Cu ou Ag et X = S ou Se ont kt6 examinks. Dans le cas des sulfures, les moments de Cr sont ordonnes antiferromagnetiquement avec TN = 40 OK dans le cas M = Cu et TN = 17 OK dans le cas M = Ag. Aucun ordre magnetique a grande distance n'est observe 5 4 OK pour Cut/~In1/2Cr2Se4, tandis que le composk M = Ag est ferromagnktique en dessous de z 60 OK. La structure magnetique de C U ~ ~ Z I ~ ~ ~ Z C ~ Z S ~ a kt6 determinee par diffraction des neutrons. Elle est b$tle a partir de quatre sous-rkseaux d'aimantation parallkles aux grandes diagonales du cube.
Abstract. - The magnetic properties of the spinels M I ~ Z I ~ I ~ Z C ~ Z X ~ with M = CU or Ag and X = S or Se were investigated. In the sulphides the Cr spins order antiferromagnetically at TN = 40 OK for M = CU and at TN = 17 OK for M - Ag. No spin ordering above 4 OK was observed in Cu ll2Inll2Cr2Se4, while AglI2In l12Cr2Se4 is ferromagnetic below TC 60 OK. The antiferromagnetic spin structure of Cul/~In1~2Cr2S~ as determined by neutron diffraction, consists of four spin sublattices with sublattice magnetizations along the cubic body diagonals.
We have investigated compounds M1/21nl/2Cr2X4 with M = Cu or Ag and X = S or Se, which crystallize in the spinel lattice with Cr occupying the octahedral sites. The valencies of the Cu containing compounds can be represented by cu:/+z~n:& I ~ r ; + 1 xi-. The monovalent Cu ions and the trivalent In ions are ionically ordered among the tetrahedral sites [I].
The magnetic behaviour of the compounds is summa- rized in table I. The X-ray diagram of
Cul/zInl,2Cr2S4
Cell edge a, molar Curie constant C,, paramagnetic Curie temperature 0, Nkel temperature TN and ferro- magnetic Curie temperature Tc of the compounds
Critical temp.
Compound a (A) C , 0 (OK) (OK)
- - - -
Cul121nl~2Cr2S4 10.060 3.83 - 77 TN = 40 C ~ , / ~ 1 n ~ ~ ~ C r , S e ~ 10.58 3.58 + 100 no
ordering Agl,21nl12Cr2S, 10.24 3.43 + 142 TN = 17 Agl121nl,2Cr2Se4 . 10.72 3.86 + 180 T, - 60
showed a pure spinel phase whereas the other samples were not completely pure. A Curie-Weiss law was observed from 300 OK to 900 OK. Our susceptibility data on C~,/,1n~Cr,Se, differ markedly from the data of Yokoyama and Chiba [2]. At 4.5 OK a moment of 5.1 pB/mole was measured on the ferromagnet
in a field of 30 kOe, at which the material was not saturated.
Of the compounds mentioned above C U ~ / ~ I ~ , ! ~ C ~ , S ~ has been studied by neutron diffraction. Figure 1
shows the spectra obtained a t 4.2 OK and room tem- perature, which is below and above the NCel tempe- rature respectively. As may be seen, the additional magnetic reflections which appear at low temperatures
(*) Philips Research Laboratories, N. V. Philips' Glceilam- penfabrieken, Eindhoven, Netherlands.
L a n 3 m 2 x 0
FIG. 1. - Neutron spectrum of C U ~ 12In112Cr2S4 at 4.2 OK and 300 OK.
may be indexed on the basis of a simple cubic magnetic cell with the same parameter as the chemical one.
Perfect 1 : 1 ordering with a reliability factor R = 3 %
was obtained from the nuclear reflections for this normal sdnel.
Various magnetic structures have been considered.
A simple one is obtained if we consider a -t- + - -
repetition of (001) sheets of parallel Cr spins along [loo] or [OlO]. Although such a structure (structure I) leads to magnetic intensities in position of the observed ones, the agreement between observed and calculated intensities is generally poor (columns 2 and 4 of table II). The agreement between observed and calcu-
Magnetic intensities at 4.2 OK ; I = jq2 I P l 2 and S = 1.35. The magnetic form factor used is the one given in the cases of MnO and MnS by CORLIS and al., Phys. Rev., (1956), 104, 924.
h k l I obs I calc I cal
str I1 str I
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711107
MAGNETIC PROPERTIES OF CuI12In~/~Cr2S4 AND SOME RELATED C 1 - 325
FIG. 2. -The octahedral sites of the spinel lattice projected on the (001) plane. In Cui12In112Cr2S4 the Cr spins on sites 1, 2, 3 and 4 are oriented along [I, 1, 11, [i, 7, 11, [I, T, i] and
[i, 1 , i] respectively.
lated intensities is much better (columns 2 and 3 of table 11) in the case of the structure (structure 11) shown in projection in figure 2. In contradistinction with structure I which is generated by one propagation vector, structure I1 is generated simultaneously by three propagation vectors : k along y-axis for M,, k along the x-axis for My and k along the z-axis for M,. The four sublattice magnetizations MI, M,, M3 and M4 are for instance oriented along the directions [I, 1, 11, [i, 1, 11, [l, 1, I] and [i, 1,1] respectively.
The Heisenberg exchange energy of structure I1 is degenerated with respect to the mutual orientations of the four sublattice magnetizations if
M , - t M , + M 3 + M 4 = 0 . The energy is :
2 W 0 - 4 W , - 2 W , - 2 W , f 4 W 4 where W, . . . W4 are the exchange interaction parame- ters for first, second, third and fourth neighbour interactions [3].
In order to understand the occurrence of the obser- ved spin configuration one has to assume that the degeneracy of the Heisenberg exchange energy is removed by some different type of interaction. Since there is little reason to expect anisotropic exchange interactions to be important for Cr3+ ions we have considered the effect of isotropic biquadratic inter- actions J,(S,.S~)' [4]. A positive J, gives indeed a minimum energy for structure 11. This is a strong indication for the existence of biquadratic exchange between Cr3+ ions in the spinel lattice.
Difficulties arise if one tries to understand the orien- tation of the spins with respect to the crystallographic axis. The single ion Cr3+ anisotropy is known to be small [5], but the positive K , makes this anisotropy energy a maximum in structure 11. Furthermore cal- culations show the magnetic dipole energy to be important [6] and to have a minimum for spin orien- tations which does not fit the neutron diffraction intensities so well as structure I1 does. Possibly consi- deration of magneto-elastic energy has to complete the picture.
Summarizing we can say that the spin structure of C U , ~ , I ~ , ~ ~ C ~ ~ S , is interesting since it shows the pre- sence of higher order exchange interactions between Cr3' ions in the spinel lattice.
The influence of the 1 : 1 ionic ordering, which gives rise to two u parameters and a crystallographic paramater for the Cr ions and the consequencies for the magnetic interactions will be discussed in a full paper 161.
Acknowledgement. - The authors are indebted to Mr. J. H. N. Creyghton for stimulating discussions and his numerical calculation of the dipolar energy, to Mr. G. H. A. M. van der Steen for preparing the samples and performing the magnetic measurements and to Mr. M. Sougi for help in the neutron diffraction work.
References
[I] LOTGERING (F. K.), VAN STAPELE (R. P.), VAN DER 141 ANDERSON (P. W.), Exchange in Insulators. Magne- STEEN (G. H. A. M.) and VAN WIERINGEN (J. S.), tism, edit. by G . T. Rado and H. Suhl, Vol. 1, J. Phys. Chem. Solids, 1969, 30, 799. New York and London, Academic Press, 1963.
[2] YOKOVAMA (H,) and CHIBA (S.), J. Phys. Soc. Japan, [ 5 ] BERGER (S. B.) and PINCH (H. L.), J. Appl. Phys.,
1969, 27, 505. 1967, 38, 949.
[3] LOTGERING (F. K.), Solid State Comm., 1965,3,347. [6] To be published.
