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

Martino Lobue (1) , Vincent Loyau (2) , Frédéric Mazaleyrat (2) , Alexander Pasko (2) , Vittorio Basso (3) , Michaela Küpferling (3) , Carlo Paolo Sasso (3)

1 SATIE-MME - Matériaux Magnétiques pour l'Energie
2 SATIE - Systèmes et Applications des Technologies de l'Information et de l'Energie
3 INRiM - Istituto Nazionale di Ricerca Metrologica

We report on the magnetic field induced isothermal entropy change, Δs(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 × 104 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.

Mots clés: barium compounds; calorimetry; cobalt compounds; crystal growth from solution; ferrites; magnetic anisotropy; spin dynamics; zinc compounds

Domaines: Science des matériaux [cond-mat.mtrl-sci]

Martino Lobue, Vincent Loyau, Frédéric Mazaleyrat, Alexander Pasko, Vittorio Basso, et al.. Direct calorimetric measurements of isothermal entropy change on single crystal W-type hexaferrites at the spin reorientation transition. Journal of Applied Physics, 2012, 111 (7), pp.07A905. ⟨10.1063/1.3670062⟩. ⟨hal-00737899⟩