Analysis of the crystallographic and magnetic structures of the Tb_0.1Pr_0.9Al₂ and Tb_0.25Pr_0.75Al₂ magnetocaloric compounds by means of neutron scattering

Neutron powder diffraction and inelastic neutron scattering data were used to simulate and understand the magnetization and heat capacity curves of the pseudobinary Tb_x Pr_1-x Al₂, with x = 0.10 and 0.25, as a function of temperature. From the Rietveld analysis, we concluded that no crystallographic transition occurs in these samples, and the high symmetry of the magnetic structure was confirmed. Moreover, the different contributions from the reflection planes could be related to the known exchange bias-like effect characteristic for the x = 0.25 sample, also suggesting the existence of some rearrangement of the magnetic moments or even the presence of spin frustration in this system. Finally, the obtained set of theoretical parameters using the mean field approach for the two systems consisting of two sublattices allowed the experimental data to be described and to explain their physical behaviors. The ensemble of our results leads us to affirm that the quadrupolar interactions as well as an existence of some rearrangement of the magnetic moments or a frustration play an important role in the strong unidirectional anisotropy and the exchange bias-like effect observed in this pseudobinary system.