Direct calorimetric measurements of isothermal entropy change on single crystal W-type hexaferrites at the spin reorientation transition

We report on the magnetic field induced isothermal entropy change, \Delta s(Ha, T), of W-type ferrite with CoZn substitution. Entropy measurements are performed by direct calorimetry. Single crystals of the composition BaCo${}_0.62$Zn${}_1.38$Fe${}_{1}6$O${}_{2}7$, prepared by the flux method, are measured at different fixed temperatures under an applied field perpendicular and parallel to the c axis. At 296 K one deduces a value of K${}_1$ = 8.7 \times 10^{4} J m${}^{-}3$ for the first anisotropy constant, which is in good agreement with the literature. The spin reorientation transition temperature is estimated to take place between 200 and 220 K.