Entropy and magnetocaloric effect in ferrimagnets RCo2

The equations of state for the magnetic and elastic subsystems of a ferrimagnet are obtained in terms of the exchange-striction model. In the formulas derived for magnetic entropy, it is represented as the sum of the contributions of two magnetic sublattices of the ferrimagnet. One of the main characteristics of the magnetocaloric effect, viz., isothermal variation Delta S (iso) of the entropy in a magnetic field, is calculated for compounds RCo2 (R = Er, Ho, Dy) that experience a first-order magnetic phase transition and TbCo2 that experiences a second-order magnetic phase transition. It is shown that the calculated values of Delta S (iso) for these compounds are in satisfactory quantitative agreement with experimental results. The change in the entropy of a ferrimagnet in a strong magnetic field upon a transition from the ferrimagnetic to ferromagnetic ordering is calculated. The peculiarities in the magnetic field dependences of the magnetic entropy of a two-sublattice ferrimagnet are analyzed.