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Abstract: The objective of this paper is the investigation of the correlations between crystal structure and the magnetization of Ni–Mn–Ga Heusler alloy. Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloy Ni52Mn25Ga23 were performed across the martensite transition temperature T M and reverse martensite transition temperature T R at atmospheric pressure. When cooling from the austenite phase, thermal strain steeply decreases because of martensite transition. Permeability suddenly increases at the Curie temperature T C =358K, indicating ferromagnetism, and suddenly decreases to around T M =328K. This indicates that the lattice transformation and magnetic phase transition correspond to each other. The percentage of contraction by martensite transition at T M and in a magnetic field is twice that in zero fields. Considering with other Ni–Mn–Ga alloys, it is supposed that the magnetic field influences the orientation of the easy c-axis along the magnetic field, and then the variant rearrangement occurs, and consequently, the variation in the strain between zero fields and non-zero field is observed. The measurement results indicate that the regions above and below T M or T R are the ferromagnetic-austenite (Ferro-A) and ferromagnetic-martensite (Ferro-M) phases, respectively. Magnetic phase diagrams were constructed from the results of the temperature dependence of thermal strain. T M and T R increase gradually with magnetic field. T M shift in magnetic fields (B) around zero magnetic field was estimated as dT M /dB=0.46K/T, indicating that magnetization influences martensite transition and the dT M /dB value is the same as that of Ni52Mn12.5Fe12.5Ga23, thereby suggesting the Ferro-M to Ferro-A transition. [Copyright &y& Elsevier]

The results of experimental investigations of the crystal structure and magnetization of the magnetic shape memory alloy Ni 2 Mn 1.48 Sn 0.52 are reported. This alloy undergoes the martensitic transition from the cubic L 2 1 -type structure to the orthorhombic 4 O -type one with decreasing temperature. The Curie temperature T C A in the austenite phase is 310 K. The magnetic state just below the martensitic transition temperature T M is the low magnetization state or something like that. With further decrease of temperature, this alloy regains the ferromagnetism. The unit cell volume contracts discontinuously at T M with decreasing temperature. The percentage of the volume change was estimated to be ∼0.7%. The nearest neighbor Ni–Mn and Mn–Mn distances in both austenite and martensite phases of Ni 2 Mn 1.48 Sn 0.52 were estimated using the X-ray diffraction analysis. On the basis of the experimental results, the magnetic properties of Ni 2 Mn 1.48 Sn 0.52 are discussed. • The martensitic transition temperature TM of Ni2Mn1.48Sn0.52 is 308 K. • The unit cell volume change of Ni2Mn1.48Sn0.52 changes discontinuously at TM with the volume contraction of ∼0.7% with decreasing temperature. • The nearest neighbor Ni-Mn and Mn-Mn distances of Ni2Mn1.48Sn0.52 was estimated using the X-ray Rietveld analysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] Magnetic phase diagram was determined for ferromagnetic shape memory alloys Ni2MnGa1−x Fe x . [•] Magnetostructural transition was found to exist between . [•] The concentration dependence of the magnetic moment per formula unit at 5K was determined. [ABSTRACT FROM AUTHOR]