Mechanism for existence of nonmagnetic cerium sites in magnetically ordered cerium compounds

Abstract

Hybridization of moderately delocalized f electrons with band electrons gives rise to a highly anisotropic two-ion interaction, which, as Siemann and Cooper first showed, accounts well for the unusual magnetic behavior of CeBi. In the present paper it is shown that the even more unusual magnetic behavior of CeSb with a succession of magnetic structures in which the higher-temperature structures (AFP) involve a periodic stacking of nonmagnetic {001} planes alternating with magnetically ordered {001} planes of [001] moment alignment can be understood on the basis of the same hybridization-mediated interionic interaction in the presence of a cubic crystal field (CF) of comparable strength. The tendency to form nonmagnetic planes, which are indeed paramagnetic in nature (Kramers doublets), is found to increase with increasing CF strength, and the stability of the AFP phases at high temperatures is shown to arise from the reconciliation of the magnetic ordering with the CF interactions. The calculations yield first-order phase transitions from a low-temperature type I antiferromagnetic phase to two high-temperature AFP phases. The possibility of a fully nonmagnetic singlet ground state, which, however, is not Kondo-like, also occurs and will be discussed.