Magnetic entropy changes of NiMnGa alloys both on the heating and cooling processes

Giant magnetocaloric effect in melt-spun Ni-Mn-Ga ribbons with magneto-multistructural transformation

“…12 If the martensitic transformation is tuned to be coupled with the magnetic transition, i.e., the magnetostructural transformation, the MCE becomes giant. 3,12 Currently, large MCE has been observed in single crystals, 3 polycrystalline bulk alloys, [12][13][14][15][16][17][18][19][20] and melt-spun ribbons 21,22 with magneto-unistructural transformation. The highest DS M of À86 J kg À1 K À1 was achieved in singlecrystalline Ni 55 Mn 20 Ga 25 alloy at a magnetic field change of about 5 T. 3 However, the high cost and complexity associated with the fabrication of single crystals becomes an unavoidable hindrance for practical applications.…”

Magnetic hysteresis and refrigeration capacity of Ni–Mn–Ga alloys near Martensitic transformation

“…The preparation and subsequent heat treatment of the polycrystalline ingots are the same as those in Refs. [15] and [16]. The x-ray powder diffraction measurements were investigated with Cu Kα radiation to prove the present samples crystallised in the non-modulated tetragonal martensitic structure at room temperature without secondary phase.…”

“…The x-ray powder diffraction measurements were investigated with Cu Kα radiation to prove the present samples crystallised in the non-modulated tetragonal martensitic structure at room temperature without secondary phase. [15,16] Magnetisation data were measured in fields from 0 to 2 T by vibrating sample magnetometer (VSM). The measurements of heating and cooling isothermal magnetisation curves were carried out by the following steps: at first, the sample was cooled to temperatures far below the Curie temperature T C and then heated to temperature near T C , after that the measurement of the isothermal magnetisation (M -H) curve began.…”

“…However, magnetic refrigeration cycle includes both heating and cooling processes and our previous studies have indicated that the magnetic entropy change could be different during heating and cooling. [15] Therefore comprehensive evaluation of hysteresis loss in Ni-Mn-Ga alloys cannot be given by research of heating or cooling process independently. Unfortunately, reports on the magnetic hysteresis of Heusler alloys usually focused on only one process, heating and cooling isothermal magnetisation processes are rarely studied together.…”

Magnetoelastic Nature of Ferromagnetic Shape Memory Effect

“…The aforementioned record-breaking values of magnetostrain, the high values of estimated magnetocaloric effect [56][57][58], and the effect of twinning-strain-induced rotation of the magnetization vector [59][60][61] are the phenomena in the focus of current research and development.…”