Anisotropy of magnetocaloric effects in easy-axis antiferromagnets

Resumo

Magnetocaloric effects (MCEs) in two-sublattice anisotropic antiferromagnets with single-ion anisotropy of easy-axis type have been investigated upon orientation of a magnetic field both along and transversely to the easy axis of magnetization. It has been shown that MCEs that arise in a longitudinal magnetic field in the paramagnetic range above the Néel temperature T_N are of a normal character, whereas in low fields in the magnetically ordered range below T_N, they are anomalous: isothermal magnetization increases magnetic anisotropy and adiabatic magnetization reduces the temperature of the antiferromagnet. Upon the magnetization of anisotropic antiferromagnets perpendicular to the easy axis of magnetization above the Néel point T_N, we observe normal (direct) MCEs that are weaker than in longitudinal fields and decrease with the relative growth of the single-ion anisotropy parameter D > 0. In low fields, upon magnetization by transverse fields below T_N, as in the case of longitudinal magnetization, anomalous (inverse) MCEs arise, but they are several orders of magnitude weaker than analogous effects in longitudinal fields and disappear completely upon passage to the limiting case of isothermal antiferromagnet.