Impact of fast-solidification on all-d-metal NiCoMnTi based giant magnetocaloric Heusler compounds

Recently, the all-d-metal Ni(Co)MnTi based Heusler compounds are found to have a giant magnetocaloric effect (GMCE) near room temperature and manifest different functionalities like multicaloric effects, which can be employed for solid-state refrigeration. However, in comparison to other traditional Heusler compounds, the relatively large thermal hysteresis (Delta Thys) and moderately steep ferromagnetic phase transition provides limi-tations for real applications. Here, we present that fast solidification (suction casting) can sufficiently tailor the GMCE performance by modifying the microstructure. Compared with the arc-melted sample, the magnetic en-tropy change of the suction-casted sample shows a 67% improvement from 18.4 to 29.4 Jkg- 1K-1 for a field change (Delta mu 0H) of 5 T. As the thermal hysteresis has maintained a low Delta Thys value (5.5 K) for the enhanced first-order phase transition, a very competitive reversible magnetic entropy change of 21.8 Jkg- 1K- 1 for Delta mu 0H = 5 T is obtained. Combining high-resolution transmission electron microscopy (HRTEM) and positron annihilation spectroscopy (PAS) results, the difference in lattice defect concentration is found to be responsible for the sig-nificant improvement in GMCE for the suction-cast sample, which suggests that defect engineering can be applied to control the GMCE. Our study reveals that fast solidification can effectively regulate the magnetocaloric properties of all-d-metal NiCoMnTi Heusler compounds without sacrificing Delta Thys.