Magneto-Structural Properties of Ni2MnGa Ferromagnetic Shape Memory Alloy in Magnetic Fields

Abstract

Abstract:The purpose of this review was to investigate the correlation between magnetism and crystallographic structures as it relates to the martensite transformation of Ni 2 MnGa type alloys, which undergo martensite transformation below the Curie temperature. In particular, this paper focused on the physical properties in magnetic fields. Recent researches show that the martensite starting temperature (martensite transformation temperature) T M and the martensite to austenite transformation temperature (reverse martensite temperature) T R of Fe, Cu, or Co-doped Ni-Mn-Ga ferromagnetic shape memory alloys increase when compared to Ni 2 MnGa. These alloys show large field dependence of the martensite transformation temperature. The field dependence of the martensite transformation temperature, dT M /dB, is −4.2 K/T in Ni 41 Co 9 Mn 32 Ga 18 . The results of linear thermal strain and magnetization indicate that a magneto-structural transition occurred at T M and magnetic field influences the magnetism and also the crystal structures. Magnetocrystalline anisotropy was also determined and compared with other components of Ni 2 MnGa type shape memory alloys. In the last section, magnetic field-induced strain and magnetostriction was determined with some novel alloys. OPEN ACCESS

Negative Magnetoresistance in Nanotwinned NiMnGa Epitaxial Films

“…The increase of Δ H p during cooling is related to the increase of magnetization variation in the nanotwins, due to the decrease of the exchange correlation length. The latter is produced by the increase of the magnetic anisotropy field 21 , 22 at low temperatures 19 .…”

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

“…The hysteresis of temperature, T R -T M was 65 K, which is much larger than that of other Ni 2 MnGa-type alloys. This is due to the large motive force in order for a martensitic transition to occur [24].…”

“…The Co-doped NiCoMnGa-type alloys turned the magnetic order of the parent phase from antiferromagnetic or paramagnetic phase, due to a large magnetization change across the transformation. As a result, it strengthens magnetic field driving force dramatically [12][13][14][15][16][17][18][19][20][21][22][23][24].…”

Фазовые переходы и тепловое расширение в сплавах Ni-=SUB=-51-x-=/SUB=-Mn-=SUB=-36+x-=/SUB=-Sn-=SUB=-13-=/SUB=-

“…Относительное из-менение линейных размеров сплавов Ni 51−x Mn 36+x Sn 13 с x = 0−3 при мартенситном превращении составляет порядка L/L ≈ 1.5 · 10 −3 (или 0.15%). В целом ха-рактер и значения относительных изменений линейных размеров образцов с 0 ≤ x ≤ 3 при мартенситном пре-вращении сравнимы с наблюдавшимися в классических сплавах Гейслера с магнитной памятью формы на ос-нове системы Ni−Mn−Ga [17,18]. Для новых сплавов Гейслера на основе сплавов системы Ni−Mn−Sn нам не удалось найти в литературе экспериментальных дан-ных об изменении размеров при мартенситном пре-вращении, а в сплавах Ni−Mn−In линейные размеры образца могут увеличиваться при фазовом переходе мартенсит−аустенит на 0.25% [19].…”