Magnetoelastic anomalies exhibited by Ni-Fe(Co)-Ga polycrystalline ferromagnetic shape memory alloy

Abstract

The martensitic transformation (MT) as well as the structure, magnetic and magnetostrain properties of a polycrystalline Ni50.1Fe18.6Ga27.2Co4.1 (at%) ferromagnetic shape memory alloy are investigated. The studied alloy exhibits a martensitic ferromagnetic phase near room temperature that shows a non-modulated tetragonal structure with a tetragonality ratio of c/a > 1. Strain measurements reveal a complex spontaneous change at MT amounting to about 0.15% that increases up to 0.22% at 5 T of the applied magnetic field indicating orientation influence of the field on the martensitic variants growth. Magnetostrain measurements enable evaluation of the magnetic field-induced strain effect in the vicinity of MT. The sample shows moderate deformation achieving values of 70 ppm related to the magnetization rotation and volume magnetostriction that does not saturate at applied magnetic field of 5 T.