Anomalous Magnetic Anisotropy Of Caged Cubic Compound Smru2zn20

The magnetic susceptibility chi, magnetization M, and specific heat C were measured for the caged cubic compound SmRu2Zn20 at temperatures down to 2K in a magnetic field H along the three principal axes of [111], [101], and [001]. A ferromagnetic phase transition was observed at T-C = 7.8K in the temperature dependences of both chi(T) and C(T). The Sm ion in SmRu2Zn20 is trivalent, which is shown by the experimental results of the lattice constant and chi(T) between 10 and 300 K. The easy axis of magnetization is the [111] direction, and the entropy at T-C is R ln 4, indicating that the ground state is quartet. These experimental results, however, contradict the simple prediction based on the cubic crystalline electric field (CEF) of Sm3+. If the ground state is quartet Gamma(8), the easy axis of magnetization should be in the [001] direction. We analyzed the anomalous magnetic anisotropy by taking into account quadrupole-quadrupole and octupole-octupole interactions as well as the cubic CEF effect, the usual exchange interaction, and the Zeeman effect.