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

TL;DR

This study measures the isothermal entropy change in single crystal W-type ferrites during spin reorientation transitions using direct calorimetry, providing insights into magnetic anisotropy and transition temperatures.

Contribution

It presents the first direct calorimetric measurements of entropy change in W-type ferrites with CoZn substitution during spin reorientation.

Findings

Entropy change measured at different fields and temperatures.

First anisotropy constant K1 determined as 8.7 x 10^4 J/m^3.

Spin reorientation transition estimated between 200 and 220 K.

Abstract

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$_16$O$_27$, 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.