Magnetic properties of ErFe₂Al₁₀ and ErRu₂Al₁₀ single crystals

We investigated the field dependences of magnetization M(H), the temperature dependences of magnetic susceptibility χ(T), and specific heat C(T) of orthorhombic ErFe₂Al₁₀ and ErRu₂Al₁₀ single crystals in a temperature range of 0.46–300 K. For ErFe₂Al₁₀, an antiferromagnetic phase transition was observed at the Néel temperature T_N 1.7 K, and M(H) of the b-axis at 0.47 K indicated a metamagnetic transition at 0.07 T. The easy axis in M(H) and χ(T) curves is the b-axis and the hard axis is the c-axis. A large anisotropy was seen in M(H) and χ(T) curves in the three crystal axes. In the case of ErRu₂Al₁₀, magnetic successive phase transitions were observed at 1.3 and 1.0 K. Spin-flops were observed in M(H) curves at 0.25 T on the a- and b-axes in 0.46 K. The easy axis in M(H) curves is the a-axis and the hard axis is the c-axis. We proposed a magnetic structure from the result of χ(T) curves, whereby the magnetic moment of Er was perpendicular to the c-axis and closely aligned to the [110] direction below T_N. The C(T) curve showed sharp peaks at corresponding temperatures. For both compounds, hump structures were observed in the temperature dependences of magnetic specific heat above T_N. These structures were Schottky anomalies that came from excited doublets.