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 thernexamined alloy the structural phase transition (SPT) and magnetic transition (MT) occur at room temperature and around 370 K,rnrespectively. The magnetic entropy change, at those two temperatures, was determined on the basis of isothermal and isofield curves,rnrecorded at fields up to 1200 kA/m (1.5 Tesla) with temperature steps of 2.5 and 5K. Although the calculated values of magneticrnentropy change are relatively small, ~0.7 J/(kg*K), an anisotropy of the MCE is observed with a magnetic field applied along thernmain crystallographic directions of the single crystal. The magnetic entropy change at the SPT depends on the orientation. Thernweakest MCE occurs when the field is applied along [1 0 0] direction whereas the highest MCE value is reached along [0 0 1]rndirection, which is an easy magnetization axis. Such behaviour can be explained with the high magnetocrystalline anisotropy of thernmartensitic phase. Astonishingly, the magnetic entropy change value, at the SPT, obtained for the polycrystalline specimen, is closernto that for the [0 0 1] single crystal direction.