Magnetic anisotropy and associated entropy change in textured TmGa

Abstract

Since Warburg's discovery of the magneto-caloric effect (MCE) in 1881, researchers have invested decades exploring its applications in the realm of magnetic cooling not only at room temperature but also at cryogenic temperatures. TmGa has emerged as a focus due to its notably high MCE performance. However, discrepancies have surfaced between the findings on single-crystalline TmGa reported by Gao et al. in 2013 and subsequent reports on polycrystalline TmGa. These disparities present significant challenges for ongoing TmGa research. To address these inconsistencies, this study prepares TmGa in a textured polycrystalline form. Magnetic measurements along both parallel (H∥a) and perpendicular (H⊥a) to the a-axis reveal pronounced magnetic anisotropy between the two directions. Notably, a distinct and complex anisotropic field-dependence in magnetic interaction and corresponding transitions are observed. Furthermore, magnetic entropy changes (∆Sm) for both H∥a and H⊥a, along with the corresponding anisotropic entropy change (∆Sman), are computed based on Maxwell’s relations. This investigation discloses maximum values of ∆Sman, reaching 17.2 J/kg K at T = 16.5 K and 24.3 J/kg K at T = 11.5 K for fields of 20 and 50 kOe, respectively, which are close to the largest value to date. These findings provide insights into fundamental magnetic properties and their potential applications for rotational magneto-caloric effects.