Frustration in R₂PdSi₃ (R ≤ Tb,Er) compounds: Spin-glass or magnetic short range order? Neutron diffraction studies

Measurements of macroscopic magnetic properties of the isostructural compounds Tb₂PdSi₃ and Er₂PdSi₃ show an additional phase transition below the ordering temperature. The behaviours of the two compounds are similar and are interpreted as spin-glass-like phase transitions in the literature. In this contribution, we present detailed neutron diffraction studies of the mechanism of the spin-glass-like phase transition on a microscopic scale. We find a fundamental difference between the two compounds in their magnetic structures and, therefore, the spin-glass-like phase transitions. In the Tb₂PdSi₃ compound an additional antiferromagnetic short range ordered phase is found within the long range ordered phase. The appearance of the short range order is linked to the spin-glass-like transition. In contrast, the Er₂PdSi₃ compound shows only long range order. However, the antiferromagnetic order undergoes a modification within the ordered state. The temperature of the transition matches the spin-glass-like transition.