Magnetization process of tetragonal antiferromagnet, ErB₂ C₂

The magnetization processes along the principal [0 0 1] axis of an antiferromagnetic ErB₂ C₂ with T_N = 15.9 K were examined by a capacitive Faraday method at temperatures down to 0.54 K in magnetic fields up to 5 T. The magnetization at 5.0 K increases up to the saturation magnetization with increasing field through five step-like transitions and decreases down to 0 μ_B through five transitions showing clear hystereses. With increasing field at 0.54 K, the magnetization starts to increase at 1.7 T and gradually reaches the saturation without any step-like increase, although ErB₂ C₂ is suggested to be an Ising-like antiferromagnet from the strong anisotropic susceptibilities. Furthermore, the process with decreasing field shows a continuous decrease down to 1.6 T, a step-like decrease at 0.7 T and a residual magnetization of 0.4 μ_B even at 0 T. It is presumed that this phenomenon may relate to the characteristic shape of Fermi surface that results in the broadest magnetic reflection with a nearly flat-top structure centered at the (1 0 0) reciprocal position.