Annealing effect on the crystal structure and exchange bias in Heusler Ni45.5Mn43.0In11.5 alloy ribbons

A Heusler Ni45.5Mn43.0In11.5 alloy has been prepared by arc melting and produced in a ribbon shape by rapid solidification using melt spinning technique. Structural properties have been investigated, at different temperatures, by using X-ray diffraction. Austenite is the stable phase at room temperature with a L21 cubic crystal structure. Exchange bias effect was observed after field cooling by means of hysteresis loop measurements. At 5 K, hysteresis loop shifts along the axis of the applied magnetic field and that shift magnitude decreases significantly with increasing temperature. A piece of ribbon was annealed at 973 K during 10 min in order to investigate the influence of annealing on crystal structure and magnetic properties. After annealing, a martensitic phase with a monoclinic 10M structure at room temperature is observed. The onset of the martensitic phase transformation shifts to 365 K, temperatures associated with both martensitic and reverse transitions do not change noticeably under an applied magnetic field up to 30 kOe, and a drastic decrease on magnetization is observed in comparison with the as-quenched ribbon meanwhile the exchange bias effect is enhanced.