Crystal Electric Field Analysis on the Magnetic Properties of Ferromagnetic CeRu 2 Ge 2 Single Crystal

We report a detailed anisotropic studies on the magnetic and transport properties of a CeRu 2 Ge 2 single crystal. A clear ferromagnetic transition is observed at T C = 7.5 K in the magnetic susceptibility, electrical resistivity and heat capacity measurements. The magnetoresistance (MR) is positive at low temperature within the magnetically ordered state. We confirmed the presence of a magnon excitation gap in the resistivity, MR and the low temperature heat capacity data. The pronounced anisotropy observed in the magnetic susceptibility and magnetization along the [100] and [001] directions is quantitatively explained within the crystal electric field (CEF) framework using the point-charge model. The analysis reveals a CEF level scheme comprising three doublets, with a ground state and two excited states at 491 and 671 K, that was further confirmed from the Schottky effect in the magnetic part of the heat capacity data. Unlike most Kondo lattice ferromagnets of Ce compounds, where the magnetic easy axis deviates from the expected CEF ground state, CeRu 2 Ge 2 exhibits magnetization, which is fully consistent with the CEF derived ground state wave function, with the easy axis of magnetization aligned along the [001] direction.