High-pressure synthesis and magnetic properties of orthorhombic CuRh ₂O ₄

Polycrystals of orthorhombic CuRh ₂U ₄ were prepared by a solid state reaction under high pressure and its magnetic properties were compared with those of polymorph-tetragonal CuRh ₂O ₄ (spinel-type compound). The orthorhombic phase undergoes antiferromagnetic transition at 24 K. The ratio of the Curie-Weiss temperature (θ _CW) to the Néel temperature (T _N) is estimated to f = |θ _CW|/T _N = 2.6 and is considerably smaller than f in the tetragonal phase, 5.3. This indicates that geometrical magnetic frustration inherent in the Cu ²⁺ network of the spinel structure is released in the orthorhombic phase with lower crystal symmetry. We observed a weak ferromagnetism below T _N in the orthorhombic phase; this is also discussed in terms of crystal symmetry.