Inverse magnetocaloric effect in Mn2NiGa and Mn1.75Ni1.25Ga magnetic shape memory alloys

Abstract

Inverse magnetocaloric effect is demonstrated in Mn2NiGa and Mn1.75Ni1.25Ga magnetic shape memory alloys. The entropy change at the martensite transition is larger in Mn1.75Ni1.25Ga, and it increases linearly with magnetic field in both the specimens. Existence of inverse magnetocaloric effect is consistent with the observation that magnetization in the martensite phase is smaller than the austenite phase. Although the Mn content is smaller in Mn1.75Ni1.25Ga, from neutron diffraction, we show that the origin of inverse magnetocaloric effect is the antiferromagnetic interaction between the Mn atoms occupying inequivalent sites.

Residual stress induced stabilization of martensite phase and its effect on the magnetostructural transition in Mn-rich Ni-Mn-In/Ga magnetic shape-memory alloys

“…The M(T ) plot in a low applied magnetic field of 50 Oe for annealed bulk samples shown in Fig. 5(a) reveals M s , M f , A s , and A f for Mn 1.75 Ni 1.25 Ga as 139, 134, 160, and 175 K, respectively, whereas the corresponding temperatures for Mn 1.9 Ni 1.1 Ga are 264, 160, 230, and 315 K. The drop at M s is related to the large magnetocrystalline anisotropy and lower magnetization of the martensite phase in these MSMAs [10,18,24]. A comparison of x-ray powder-diffraction profiles of the as-ground powder samples and the same powder after it was annealed at 773 K for 10 h (Fig.…”

“…The austenite phase of Mn excess Ni-Mn-In alloys is known to be ferromagnetic whereas the martensite phase is generally believed to be nonmagnetic (either paramagnetic or antiferromagnetic) [6,8,11], whereas in the Mn excess Ni-Mn-Ga alloys, both the austenite and the martensite phases are reported to be ferrimagnetic [10,[16][17][18]. Using high-resolution synchrotron and laboratory x-ray powder-diffraction (XRD) data, it is shown that the martensite structure can be stabilized by residual stresses over a wide temperature range well above A f in both alloy systems.…”

“…Recent years have witnessed a tremendous surge in the study of ferroic and multiferroic materials exhibiting giant caloric effects that can be used in solid-state refrigeration at temperatures close to the ambient conditions as an environmentally friendly substitute to conventional vapor compression refrigeration [1][2][3][4][5]. The Heusler-type Mn-rich Ni-Mn-X (X = Ga, In, Sn, or Sb) magnetic shape memory alloys (MSMAs) have emerged as a potential family of alloys that can exhibit giant barocaloric, elastocaloric, and inverse magnetocaloric (i.e., cooling during magnetization and heating during demagnetization in contrast to normal magnetocaloric materials which heat up on magnetization and cool down by its removal) effects [6][7][8][9][10]. The giant inverse magnetocaloric effects (MCEs) and barocaloric effects (BCEs) in these alloys are linked with a first-order martensitic transition, which is a magnetostructural transition involving change in crystal structure as well as huge drop in magnetization ( M) between the austenite and the martensite phases [11].…”

A switch-like magnetoresistance of ferromagnetic Ni–Mn–Ga ribbon during martensitic transformation

“…These kinds of alloys not only have a very large magneticfieldinduced strain (MFIS) [3] [4]), but also possess other useful properties in regard to martensitic phase transformation, such as their very large magnetocaloric effect (MCE) and strong magnetoresistance (MR) [5][6][7][8][9][10][11][12][13][14][15]. This very large MFIS is due primarily to the rearrangement of martensitic variants, but it is  Corresponding author: Qingxue Huang Email address: qxhuang_pd@163.com obtained only in single crystals.…”

Магнитокалорический эффект и эффект памяти формы в сплаве Гейслера Mn-=SUB=-2-=/SUB=-NiGa

“…В последние годы сплавы Гейслера системы Mn 2 NiZ (Z = Ga, In, Sn, Sb) привлекли большой интерес исследователей, как ферромагнитные сплавы с эффектом памяти формы (ЭПФ) и полуметаллы (ферроили ферримагнетики), вследствие интересных физических свойств и потенциального применения для создания магнитных актюаторов и спинтронных устройств [1][2][3][4][5][6][7][8][9][10]. Исследования данных сплавов были простимулированы открытием магнитоиндуцируемых деформаций (4%) в монокристалле Mn 2 NiGa, обладающим термоупругим мартенситным фазовым переходом (ФП) вблизи комнатной температуры -270 K, и высокой температурой магнитного ФП -588 K [1].…”