Magnetocaloric effect in Ni-Mn-In-Co microwires prepared by Taylor-Ulitovsky method
(School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China)
Abstract: Ni-Mn-In-Co microwires with diameter of 30-100 μm are prepared by glass-coated metal filaments (Taylor–Ulitovsky) method. The effects of magnetic field on martensite transformation temperature in the as-prepared and annealed microwires are investigated using a physical property measurement system (PPMS). Magnetocaloric effect (MCE) attributed to field-induced austenite transformation in the as-prepared and annealed microwires is analyzed indirectly from the isothermal magnetization (M-B) curves. The as-prepared microwire has a 7-layer modulated martensite structure (7M) at room temperature. The changes of austenite starting temperature induced by an external magnetic field (ΔAs/ΔB) in the as-prepared and annealed microwires are -1.6 and -4 K/T, respectively. Inverse martensite to austenite transformation exists in annealed microwires when an external magnetic field is applied at temperatures near As. The entropy change (ΔS) obtained in the annealed microwires is 3.0 J/(kg？K), which is much larger than that in the as-prepared microwires 0.5 J/(kg？K). The large entropy change and low price make Ni-Mn-In-Co microwires a potential working material in magnetic refrigeration.
Key words: magnetic shape memory alloys; microwires; martensitic transformation; magnetocaloric effect; magnetization curve