Magnetocaloric effect due to spin reorientation in the crystalline electrical field: Theory applied toDyAl2

Abstract

We report a way of obtaining the magnetocaloric effect due to the crystal electrical-field quenching of the total angular momentum in a magnetic system where a strong spin reorientation is present. The theoretical model is applied to DyAl 2 and the results predict a considerable magnetic entropy change by rotating a single crystal in a fixed magnetic field. The obtained temperature and magnetic-field dependencies of the magnetization component along the ͗111͘-crystallographic direction are in good agreement with the recently reported experimental data.

The anisotropic magnetocaloric effect described by Maxwell formulation: Application to DyAl2 and TbNi2

“…[9], and references therein). The DyAl 2 presents cubic symmetry and orders ferromagnetically below 61 K with the easy axis along the [1 0 0] direction.…”

“…In order to perform the calculations in the anisotropic DyAl 2 compound we used the same set of CEF and exchange parameters considered in Ref. [9]. The magnetization isotherms curves were calculated changing the magnetic field (of fixed intensity H = 5 T) from [0 0 1] to [1 1 1] direction, in a plane defined by these directions, i.e., fixing the azimuthal angle at = /4 and varying the angle Â.…”

“…On the other hand, the isothermal and adiabatic anisotropic-MCE potentials were introduced in a recent work by von Ranke et al [9]. To do this it was necessary to define the set (˛e,ˇe, e ) which describes the angles formed between the applied magnetic-field vector (in the easy magnetic direction) and the Cartesian axes x, y, and z, respectively.…”

“…From this Hamiltonian, the energy eigenvalues, ε n , and eigenvectors, |n , are numerically determined to calculate the magnetization components. Details of the calculations of magnetization and entropy were described elsewhere [9]. In short, for a given magnetic field direction, one can use relations (9) and (10) to obtain the magnetization components˛= (x, y, z) as well as the directional magnetic entropy of the magnetic system under investigation.…”

Investigation on the magnetocaloric effect in DyNi2, DyAl2 and Tb1−Gd Al2 (n=0, 0.4, 0.6) compounds

“…However, for anisotropic magnetic materials where the magnetization dependence on the magnetic field direction is relevant it is convenient to define these magnetocaloric quantities for a relative rotation of the applied magnetic field (of constant intensity) from one direction to another non-equivalent crystallographic direction [2].…”