Comparative Study of Structural and Magnetic Properties of Bulk and Powder Ni$_{52}$Fe$_{17}$Ga$_{27}$Co$_{4}$ Magnetic Shape Memory Alloy

Abstract

The Ni-Fe-Ga-Co system has been proposed as a new magnetic shape memory alloy due to its wide temperature range for martensitic and magnetic transformations (Tm and Tc , respectively) by changing composition. The alloy composition Ni52Fe17Ga27Co4 is more interesting for practical application due to its relatively high Tm and Tc. Here, martensitic transformations, crystal structures, and magnetic properties of Ni 52Fe 17Ga 27Co 4 alloys in form of bulk and powder are studied. Bulk samples were prepared by arc-melting followed by annealing at 1473 K for 4 h, while powder samples were filed from this bulk sample and annealed at 673 K for 0-15 h. The martensitic transformation present in the bulk sample totally disappears after powderisation. Tc of the powder sample is about 100 K lower than that of the bulk one. The saturation magnetization of the bulk sample (Msat = 54 emu/g) is reduced significantly down to 35 emu/g by powderisation, but increased again with increasing annealing time. After annealing the powder for 15 h, the martensitic transformation recovers and Tc is increased close to the level of the bulk sample. From room-temperature X-ray diffraction, it is found that the tetragonal non-modulated martensite in the bulk sample is completely transformed to a disordered fcc phase by powderisation, but gradually changes into a highly ordered L21 austenite phase during the subsequent annealing.