Reentrant Spin Glass and Mixed Phases in Amorphous EuTiO₃

Amorphization of magnets disturbs the various competing exchange interactions and gives unique magnetic properties. Such unique properties are evident in amorphous EuTiO₃ (ETO) films as it exhibits ferromagnetic (FM) order in contrast to its crystalline antiferromagnet counterpart. Here we present the consequences of amorphization of ETO - the existence of reentrant spin glass (RSG) phase and the mixed phase of RSG and FM ordering using AC susceptibility (χ). The amorphous films were prepared with pulsed laser deposition. The FM and RSG phase transitions are observed around T_c = 6.2 K and T_SG = 4.2 K respectively. To understand the magnetic nature of RSG, the linear and non-linear χ have been measured. The real and imaginary linear χ exhibit peaks at the two phase transitions. The peak at T_c is frequency independent while the other peak at T_SG shifts to higher temperatures with decreasing height as the frequency is increased. The presence of χ₂ signal even below T_SG indicates the coexistence of SG state with FM order. Moreover, the divergence of χ₃ at T_SG confirms the RSG phase transition.