Reduced Hysteresis and Enhanced Giant Magnetocaloric Effect in B-Doped all-d-Metal Ni-Co-Mn-Ti-Based Heusler Materials

The all-d-metal Ni-(Co)-Mn-Ti-based Heusler alloys are found to show a giant magnetocaloric effect near room temperature and are thereby potential materials for solid-state refrigeration. However, the relative large thermal hysteresis and the moderate ferromagnetic magnetization provides limitations for real applications. In the present study, we demonstrate that introducing interstitial B atoms within Ni36.5Co13.5Mn35Ti15 alloys can effectively decrease the thermal hysteresis Delta T-hys (down to 4.4 K), and simultaneously improve the saturation magnetization (maximum 40% enhancement) for low concentrations of B doping (up to 0.4 at. %). In comparison to the undoped reference material, the maximum magnetic entropy change (Delta S-m) for the Ni36.5Co13.5Mn35Ti15B0.4 alloy shows a remarkable improvement from 9.7 to 24.3 J kg(-1) K-1 for an applied magnetic field change (Delta mu H-0) of 5 T (30.2 J kg(-1) K-1 for Delta mu H-0 = 7 T). Additionally, due to the obtained low thermal hysteresis Delta T-hys, the maximum reversible Delta S-m(rev) amounts to 18.9 J kg(-1) K-1 at 283 K for Delta mu H-0 = 5 T (22.0 J kg(-1) K-1 at 281 K for Delta mu H-0 = 7 T), which is competitive to the traditional Ni-Mn-X-based Heusler alloys (X = Ga, In, Sn, Sb). The enhancement of the magnetic moments by B doping is also observed in first-principles calculations. These calculations clarify the atomic occupancy of B and the changes in the electronic configuration. Our current study indicates that interstitial doping with a light element (boron) is an effective method to improve the magnetocaloric effect in these all-d-metal Ni-Co-Mn-Ti-based magnetic Heusler compounds.

Automated summary

In this study, it is found that introducing interstitial B atoms can effectively decrease thermal hysteresis and improve saturation magnetization in Ni-(Co)-Mn-Ti Heusler alloys, thereby enhancing the magnetocaloric effect and making it competitive.