Phase Transitions and Diagrams of Pseudo-binary Antiferroquadrupolar Ordering Compound Ho_1−xTb_xB₂C₂ (0≤x≤1)

Abstract

We performed precise experiments of specific heat and magnetization on single-crystalline samples of pseudo-binary antiferroquadrupolar ordering compounds Ho_1−xTb_xB₂C₂ (0≤x≤1). Although the Tb³⁺ ions do not participate in the AFQ order in phase III of HoB₂C₂ that is a coexistent phase of AFQ and antiferromagnetic order, these are cooperative with the AFQ ordering and sustain phase III up to x=0.6. In Ho_0.4Tb_0.6B₂C₂, phase III is separated into phases III_Ho and III_Tb, where these are similar to phase III in HoB₂C₂ and TbB₂C₂, respectively. This implies that the magnetic structures are different between phases III_Ho and III_Tb. It originates in different antiferromagnetic interactions between both compounds.