The effect of Er doping on the spin reorientation transition in Ho1−xErxAl2

The magnetothermal properties of pseudo binary Ho_1−xEr_xAl₂ alloys have been investigated by heat capacity measurements. Two anomalies are observed in the heat capacity of HoAl₂. A sharp peak at 20 K represents the first order spin reorientation transition, and a second order anomaly occurs in the vicinity of the ferromagnetic transition at 32 K. As Ho is partially replaced by Er in Ho_1−xEr_xAl₂ the sharpness of the first order heat capacity peak diminishes with increasing Er concentration, while the temperature of this transition remains practically unaffected. The second order ferromagnetic transition shifts to higher temperature region with increasing Er concentration. The observed behaviors are explained considering the geometry of 4f charge densities of Ho³⁺ and Er³⁺ and the easy magnetization directions of HoAl₂ and ErAl₂.