Martensite transformation behavior and magnetocaloric effect in annealed Ni-Co-Mn-Sn microwires

Abstract Effect of annealing on martensite transformation (MT) and magnetocaloric effect (MCE) in a Ni41.3Co6.3Mn42.4Sn10.0 microwire was investigated. After annealing at temperatures 723–1173 K, the MT temperatures and Curie points shifted to higher range; meanwhile, the thermal hysteresis (ΔThys) decreased. However, partial transition arrest appeared when annealed at temperatures > 1073 K, leading to decreased magnetization difference (ΔM) between martensite and austenite phases. The maxima ΔM and minima ΔThys were produced at an annealing temperature 1023 K. Consequently, a large magnetic entropy change ( Δ S M max ) 20.1 J/kg·K, wide working temperature span (ΔTFWHM) 20 K and thus high effective refrigeration capacity (RCeff) 197 J/kg were obtained under a magnetic field 5.0 T after annealing at 1023 K for 1 h. These facts make Ni-Co-Mn-Sn microwires promising for miniature refrigeration devices due to their high specific surface area, low thermal hysteresis and markedly reduced annealing temperature and time.