Effect of Ferromagnetic Exchange and Magnetic Field Orientation on the Magnetocaloric Effect of Uniaxial Van Vleck Paramagnet

The magnetocaloric effect (MCE), namely, the magnetic entropy change upon the isothermal magnetization of a uniaxial Van Vleck paramagnet with a spin of S = 1 and single-ion easy-plane magnetic anisotropy has been studied in this work. It has been shown that, upon magnetization along the easy plane, the value of normal MCE (decrease in the entropy upon magnetization) can be anomalously high, when the ratio of anisotropy and ferromagnetic exchange parameters of a paramagnet is close to a threshold value corresponding to the transition to the ferromagnetic state. It has been found that, upon magnetization along the hard magnetization direction, i.e., perpendicular to the easy plane, the MCE at low temperatures demonstrates anomalous behavior, namely, the magnetic entropy increases upon magnetization.