Spin Axis Reorientation Transition in Canted Antiferromagnet : Mn(HCOO)₂·2H₂O

By the measurement of A C magnetic susceptibility, the field induced reorientation transition in Mn(HCOO) 2 ·2H 2 O was observed over the temperature range from 1.3°K to 3.7°K( T N ). The transition could be verified by the change of the angular pattern of proton resonance. The threshold field, H th , was found to be proportional to | T - T R | 1/2 near the spontaneous reorientation transition temperature, T R (1.7°K). The temperature dependence of H th could be accounted for by the relation \(Hₜₕ{=}√{2HE|HA|}\) considering the competing two sorts of anisotropy energies which have different temperature dependences. The angular dependence of H th on the external field direction was given by a hyperbolic relation in the b - d plane and by an elliptic one in the a - c plane. This dependence is discussed phenomenologically.