Magnetic Properties of an Antiferromagnetic Orthoferrite

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Abstract
The orthoferrite DyFeO3, weakly ferromagnetic at room temperature, was found to become antiferromagnetic at 36°K. Symmetry considerations suggest that at this transition point the iron spin-axis rotates out of the plane perpendicular to the Moriya-Dzyaloshinsky vector, becoming parallel to it. On this basis the magnetic point group mmm is assigned to DyFeO3 below the transition. Further evidence for the correctness of this assignment has been obtained by the observation of a linear dependence of the susceptibility on the magnetic field χxy=CHz, and cyclic permutations as allowed by the mmm symmetry. Another transition, which we associate with an antiferromagnetic ordering of the Dy3+ moment, is found at TN=3.7°K. The magnetization curves measured below 4.2°K at fields up to 40 kG are interpretable, to a good approximation, in terms of |±15/2〉 Kramers' doublet whose axis lies in the mirror plane of the crystal, making an angle of approximately 30° with the [010] axis. Below TN metamagnetic transitions were observed. Symmetry arguments show that provided the chemical and magnetic unit cells are identical, the magneto-electric effect is allowed in DyFeO3 below TN.