Structural ordering, magnetic and electrical transport properties in Ni60-xFe13+xGa27 Heusler alloys

The evolutions of phase transformation, magnetic and electrical transport properties with the change of Fe concentration have been systematically investigated in a series of Ni60-xFe13+xGa27 (x = 0-10) Heusler alloys. The structure and heat flow measurements reveal every sample undergoes a disordered-ordered transition from a disordered B2 structure to a L21 ordered structure, and a first-order structural transformation from the L21 cubic structure to a L10 tetragonal structure is corresponding to the martensitic transformation (MT). With increasing Fe concentration, the disordered-ordered transition and ferromagnetic transition shift to higher temperature, while the MT shifts to lower temperature. According to phase diagram es-tablished in the present investigation, it is also found that the increase of Fe content can convert the first -order MT from a paramagnetic type to a ferromagnetic one, which is accompanying by an obvious increase of both effective and spontaneous magnetic moments. Furthermore, the calculated magnetocrystalline anisotropy constant (K1) of the studied alloys monotonically increases as Fe increases. It is evident that the magnetic degrees of freedom in these two MTs remain almost unchanged so that the electron-spin scat-tering doesn't change, which results in the resistivity difference between the austenitic and martensitic states is feeble. Such an intrinsic nature leads to a weak magnetoresistance (MR) and baroresistance (BR) effects in the studied samples because of only contribution of electron-lattice scattering change on the resistivity. This demonstrates from a negative perspective that the electron-spin scattering change origi-nated from the variation in the magnetic degrees of freedom acts as a dominant role in improvement of the MR and BR effects for the Heusler system possessed the first-order MT.(c) 2022 Elsevier B.V. All rights reserved.