The low-temperature magnetism of cerium atoms inCeMn2Si2 and CeMn2Ge2 compounds

Abstract

The low-temperature magnetic properties of the Ce atoms in the intermetallic compoundsCeMn2Ge2 and CeMn2Si2 were studied. Previous neutron scattering measurements did not detectan ordered moment at Ce atoms in either compound despite the fact thatthey are surrounded by the Mn moments ordered ferromagnetically in theCeMn2Ge2 and antiferromagneticallyin the CeMn2Si2. Contrasting with this result, a recent measurement performed with the timedifferential perturbed angular correlation (TDPAC) technique showed thepresence of a pronounced magnetic hyperfine field (MHF) at Ce sites in theCeMn2Ge2 compound andno MHF in CeMn2Si2. The absence of the Ce magnetic moment and MHF in the silicide can be understood interms of too weak a Ce–Ce magnetic interaction while in the germanide the TDPACresult suggests that some magnetic ordering of Ce atoms may occur. Aiming tounderstand the effects which result in the quenching of the Ce 4f moment inboth cases, we performed first-principles band-structure calculations for bothsystems, using the full potential linear augmented plane wave method. It is shownthat the magnetism of the Ce sublattice has fundamentally different nature inCeMn2Si2 and CeMn2Ge2. While the Ce atoms are intrinsically non-magnetic in the silicide, having a zero magnetic momentwith both spin and orbital contributions identically zero, they display magnetic properties in theCeMn2Ge2 since their very small total moment is composed of finite spin and orbital componentswhich almost cancel each other accidentally.