Antiferromagnetism and geometric frustration in tetrahedral lattice hydroxyhalides M₂(OH)₃X

Abstract

A systematic study of magnetic susceptibility measurements is carried out on distorted tetrahedral lattice hydroxyhalides Fe2(OH)3Cl, Mn2(OH)3Cl, Mn2(OH)3Br, and Co2(OH)3Br, following our recent finding of coexisting antiferromagnetic order and disorder in Cu2(OH)3Cl (clinoatacamite). These transition metal hydroxyhalides are found to undergo antiferromagnetic transitions, at TN = 14 K for Fe2(OH)3Cl, at two successive transitions of TN1 = 3.4 K and TN2 = 2.7 K for Mn2(OH)3Cl, at TN1 = 3.3 K and TN2 = 2.4 K for Mn2(OH)3Br, and at TN = 5 K for Co2(OH)3Br, respectively. All hydroxychlorides show coexisting glassiness below the magnetic transitions; meanwhile, the glassiness is not found in the hydroxybromides. The distorted tetrahedral lattice for the magnetic ions consists of stacked layers of triangular lattice planes and Kagome lattice planes, with the magnetic ions on the Kagome lattice planes being bonded by the halogen ions. The contrasting behaviours in Mn2(OH)3Cl and Mn2(OH)3Br suggest that the glassiness arises from competing magnetic interactions in the tetrahedron, specifically on the Kagome lattice planes.