Novel field-induced magnetic transitions of GdMn₂Ge₂

Magnetization curves were measured for GdMn₂Ge₂ single crystals, which show a first-order magnetic transition from a ferrimagnetic state to an antiferromagnetic state at T₁ = 95 K. The field-induced transition from the ferrimagnetic state to a high-field state was observed for both H ⊥ c and H ∥ c below T₁. The transition field, H_C, in H ⊥ c goes to zero with increasing temperature to T₁, while that in H ∥ c gradually decreases without falling to zero at T₁. The results were analyzed in terms of a molecular field approximation, in which strong strain dependence of the interlayer Mn-Mn interaction was taken into consideration. The experimental data are well reproduced by the calculated results. The calculations predict that the compound undergoes double magnetic transitions in high magnetic fields for H ∥ c just above T₁, which was confirmed by the measurements.