Martensitic Transformation in Ni–Mn–Ga Alloy Under High Magnetic Fields

Abstract

An effect of magnetic field on the martensitic transformation (MT) temperature in ferromagnetic shape memory Ni 49:4 Mn 27:7 Ga 22:9 single crystal with the MT temperature 285 K is studied by measuring and theoretical treatment of the magnetization versus temperature dependencies in a wide range of the high magnetic fields higher than saturating one. In this way, a linear approximation of the field dependence of MT temperature was proved for the high-field range. The linear increase of transformation temperature is characterized by the slope of 3:5 Â 10 À2 K/kOe. This value is essentially larger than the value 2 Â 10 À2 K/kOe reported by Gonzales-Comas et al. [Phys. Rev. B 60 (1999) 7085-7090] for the Ni 49:5 Mn 25:4 Ga 25:1 alloy with a low MT temperature. This difference is in an agreement with the predictions of the Landau theory.

Autonomous generator based on Ni-Mn-Ga microactuator as a frequency selective element

“…These shifts result in a decrease of signal frequency by about 9.5%. So, the wellknown effects of positive shifts of transformation temperatures under magnetic field and/or stress in NiMnGa [5,6,8] will inevitably result in a decrease of the frequency.…”

“…When MT occurs in the ferromagnetic austenite, a magnetic field shifts T m upwards [5], this shift being about ten times larger in a value for MT merged with Curie temperature, T C [6]. In addition, Ni MnGa thin films deposited on Al 2 O 3 or glass substrates demonstrate a thickness dependence of both T m and corresponding resistivity anomaly [7,8].…”

Thermodynamics and Kinetics of Martensitic Transformation in Ni-Mn-based Magnetic Shape Memory Alloys

“…Equation 5 can be found in many reports in the field of Ni-Mn-based alloys both because of the easy access of moderately strong magnetic fields as well as interest in the magnetocaloric effect [84][85][86]. For Ni-Mn-Ga ternary alloys, the magnetization of martensite phase is greater than that of the parent phase [87], and therefore a strong magnetic field generally raises the T M s [88][89][90]. However, due to the large magnetic anisotropy in Ni-Mn-Ga alloys [2,91], a low magnetic field results in a small decrease of T M s [88,89].…”

“…For Ni-Mn-Ga ternary alloys, the magnetization of martensite phase is greater than that of the parent phase [87], and therefore a strong magnetic field generally raises the T M s [88][89][90]. However, due to the large magnetic anisotropy in Ni-Mn-Ga alloys [2,91], a low magnetic field results in a small decrease of T M s [88,89]. Nevertheless, for Ni-Mn-In alloys, the magnetization of the parent phase is much greater than that of martensite phase, and thus magnetic fields will effectively decrease the T M s [23,[92][93][94][95][96], as is schematically shown in Fig.…”

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

“…A: Magnetic field influence on martensite transformation in ferromagnetic shape memory alloys and metamagnetic shape memory alloys [64][65][66][67][68][69][70]; B: Magnetic anisotropy of the ferromagnetic shape memory alloys [71,72]; C: Magnetostriction [73,74].…”