COMPOSES DE TERRES R A M ET cOMPOSL % DlCTfNlDES- MAGNETOCHEMICAL AND MAGNETIC PROPERTIES OF AB2S4 TYPE COMPOUNDS

Rhum6.- L'ktude des relations entre les propriktks klectriques, la distance ionique, la valence (contr6lCe par dkpla-cement isomkrique de 151Eu) et les propriktks magnktiques de composks de type AB2S4 (A = EuZ+, B une terre rare (R3+) Y, Sc) a structure cubique-Th3P4, orthorhombique-CaFez04 et hexagonal-PbCrzS4 (ou B = Cr3+) revkle un compor-tement antiferromagnktique de tous les composks de type EuR2S4 au-dessous de 4 OK (a l'exception de EuSczS4, Te = 13 OK), par contre EuCrzS4 devient ferrimagnktique 9. partir de TN = 68 OK. Les rksultats montrent que le dep6t de conclusions sans equivoque sur la valence et le moment magnktique, lorsque diffkrents cations sont en presence, necessite un cornplkment des informations a I'aide de mkthode microscopique. Abstract.- Relations between electric properties, cation distances, valencies (controlled by 151Eu isomer shifts) and the magnetic properties of ABzS4-type compounds (A = Euz+, B = Rare Earth (R3+) Y, SC) displaying cubic Th3P4-, orthorhombic CaFezO4- and hexagonal PbCrzS4-structure (with B = Cr3+) reveal antiferromagnetic behaviour below 4 OK for all EuR2S4 compounds (exception EuSC~S ~ , Tc = 13 OK), whereas EuCrzS4 becomes ferrimagnetic at TN = 68 OK. The. results demonstrate that unambiguous conclusions on valencies and magnetic moments in the presence of different types of cations need additional informations by microscopic methods. I. Cubic and orthorhombic EuRzS4 compounds.-(R = rare-earth-ion.) With A being a divalent metal