Thermomagnetic phenomena in hexagonal ferrimagnetic materials

The results of an investigation of the magnetocaloric effect in the CoTi-M and CoZn-W hexaferrite systems in the 150–500 K temperature range are presented. It is shown that the maxima of the magnetocaloric effect correspond to spontaneous spin-orientational transitions leading to transformation of the magnetic structure from easy-plane to uniaxial and to resultant changes in the values and signs of the magnetic anisotropy constant as a function of the composition and temperature. Estimates of the ΔT(T) relation taking into account the magnetic anisotropy constants K1, K2, and K3, which are known for the compounds considered, agree well with experiment. Hence, the main contribution to the magnetocaloric effect at temperatures far from the Curie point in the materials in question is governed by the rotation of the magnetization vector.