Highly anisotropic 1/3-magnetization plateau in a ferrimagnet Cs2Cu3(SeO3)4·2H2O: topology of magnetic bonding necessary for magnetization plateau.

We prepared Cs2Cu3(SeO3)4·2H2O composed of Cu2+ ions at square-planar coordination sites and characterized its structural and magnetic properties, to show that Cs2Cu3(SeO3)4·2H2O is a ferrimagnet exhibiting a highly anisotropic 1/3-magnetization plateau. This unprecedented anisotropy in a magnetization plateau is the consequence of three effects, namely, the orthogonal arrangements of the corner-sharing CuO4 square planes, the nearest-neighbour antiferromagnetic exchange, and the anisotropic g-factor of the Cu2+ ions at square-planar coordination sites. By analyzing the topology of magnetic bonding, we found why magnetic plateaus are observed only for certain ferrimagnets and antiferromagnets.