ANISOTROPY OF THE MAGNETOCALORIC EFFECT IN THE SINGLE CRYSTALLINE Ni_(49.6)Mn_(27.6)Ga_(22.8) ALLOY

摘要

The magnetocaloric effect (MCE) anisotropy in the Ni_(49.6)Mn_(27.6)Ga_(22.8) single crystal was investigated. In the examined alloy the structural phase transition (SPT) and magnetic transition (MT) occur at room temperature and around 370 K, respectively. The magnetic entropy change, at those two temperatures, was determined on the basis of isothermal and isofield curves, recorded at fields up to 1200 kA/m (1.5 Tesla) with temperature steps of 2.5 and 5K. Although the calculated values of magnetic entropy change are relatively small, ～0.7 J/(kg*K), an anisotropy of the MCE is observed with a magnetic field applied along the main crystallographic directions of the single crystal. The magnetic entropy change at the SPT depends on the orientation. The weakest MCE occurs when the field is applied along [1 0 0] direction whereas the highest MCE value is reached along [0 0 1] direction, which is an easy magnetization axis. Such behaviour can be explained with the high magnetocrystalline anisotropy of the martensitic phase. Astonishingly, the magnetic entropy change value, at the SPT, obtained for the polycrystalline specimen, is close to that for the [0 0 1] single crystal direction.