Observation of Spontaneous Magnetization in the Layered Perovskite Ferromagnet, (p-Chloroanilinium)₂CuBr₄

The crystal structure and magnetic properties of the layered perovskite, (p-chloroanilinium)(2)CuBr(4) (1) have been investigated. The crystal of 1 belongs to the orthorhombic Pbca space group [a = 7.551(2) Å, b = 32.082(10) Å, c = 7.879(2) Å, and Z = 4], which is typical of the material family. The temperature dependence of the ac susceptibility (chi(ac) = ( partial differentialM/ partial differentialH)) of a polycrystalline sample shows magnetic ordering at 15 K with an abrupt increase of the value. In the ordered state, the field dependence of chi(ac), namely the differential susceptibility, and the dc magnetization indicate a hysteresis loop of the magnetization, which can be ascribed to the presence of spontaneous magnetization. Furthermore, single-crystal magnetic measurements indicate that the magnetic properties of 1 are quite anisotropic. When the field is along the b axis (perpendicular to the inorganic layer), the field dependence of chi(ac) shows the hysteresis behavior, as observed for the polycrystals, but when it is parallel to the a axis (parallel to the layer), chi(ac) shows metamagnetic transitions. The observed anisotropy can be understood in terms of a magnetic easy axis parallel to the a axis, an antiferromagnetic interlayer interaction, and a spin canting which produces spontaneous magnetization along the b axis.