A criterion for enhancing the giant magnetocaloric effect: (Ni–Mn–Ga)—a promising new system for magnetic refrigeration

Abstract

This letter reports a giant magnetocaloric effect (GMCE) in a novel series of materials based on the shape memory alloy Ni 2 MnGa. The origin of an enhanced GMCE is traced to the coincidence of a first-order magnetic transition and its attendant structural phase transition with a second-order magnetic transition. This coincidence is achieved by careful compositional tuning and is a technique which provides a criterion for enhancing the GMCE in this system. Thus, for Ni 55.2 Mn 18.6 Ga 26.2 , we report an entropy change S m = −20.4 J kg −1 K −1 at 317 K in a field of 5 T. This shape memory system also has the added advantage of being formed from inexpensive, nontoxic constituents. With a working temperature at and above room temperature, it appears to be a most promising candidate for practical room temperature magnetic refrigeration.

Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa

“…[11,12] For example, varying x from 0 to 0.2 causes T C to decrease from 376 to 325 K and T M to increase from 210 to 325 K. Giant-magnetocaloric effect has been observed in samples where T C and T M are equal. [8,13] In this paper, we report 5% negative magnetoresistance (MR) at 8 T in bulk Ni 2+x Mn 1−x Ga polycrystals at room temperature. To the best of our knowledge, there are no MR studies in literature till date on well characterized bulk Ni 2+x Mn 1−x Ga samples as functions of composition and temperature.…”

Structural modulations and magnetic properties of off-stoichiometric Ni-Mn-Ga magnetic shape memory alloys

“…44 The field-dependent magnetization curves of the sample at 300K are shown in Figure 4(c), where the material is in the ferromagnetic martensite phase. The magnetization of the sample is fully saturated at the applied field of 1.0 T along [010], the saturation magnetic moment at 300 K is 2.67 μB per formula unit of Ni 2 Mn 1.14 Ga 0.86 .…”

Peculiarities of magnetoelastic coupling in Ni–Fe–Ga–Co ferromagnetic martensite

“….H\ZRUGV ferromagnet; shape memory alloy; martensite; magnetostriction Magnetically ordered alloys undergoing a thermoelastic martensitic transformation have been attracting considerable attention due to the possibility of inducing large strains by magnetic field [1,2] and producing high magnetocaloric effect [3,4]. These alloys demonstrate a number of structural modifications, both in the martensitic and parent phases, like magnetic anomalies [5][6][7][8][9] and intermartensitic transformations [10][11][12][13][14] a clear physical origin for which is still lacking.…”