Crystal Field Effects in Polymorphic Compound TbIr2Si2

Abstract The tetragonal ternary compound TbIr 2 Si 2 shows polymorphism; the ThCr 2 Si 2 -type structure as a low temperature phase (I-phase) and the CaBe 2 Ge 2 -type one as a high temperature phase (P-phase) exist. In order to compare with magnetism of the morphs, magnetic measurements were performed on the I- and P-phase single crystals. The magnetic behavior changes drastically depending on the structure. The TbIr 2 Si 2 (I) shows an antiferromagnetic ordering below T N =80 K, a strong uniaxial magnetic anisotropy with the easy [001] direction, and isotropic magnetic behavior in the basal plane. The [001] magnetization shows a clear two-step metamagnetic transition: an Ising-like behavior at low temperatures. On the other hand, the TbIr 2 Si 2 (P) has the comparatively low ordering temperature of T N1 =11.5 K and an additional transition temperature of T N2 =5 K, and exhibits an easy-plane magnetic anisotropy with the easy [100] direction. A strong magnetic anisotropy appears for high magnetic fields between the directions in the basal plane. Multi-step metamagnetic processes appear. In the both phases, the χ - T behavior suggests the existence of component-separated magnetic transitions. The ab -component of magnetic moments orders at the higher transition temperature T N1 for the P-phase compound, which is contrast to the I-phase behavior; the c -component orders firstly at T N in the I-phase. The crystalline electric field analysis was made, and the CEF effects explain the different of magnetic anisotropy between the both phases.