Magnetocaloric refrigeration is one of the most promising next-generation solid-state caloric techniques to revolutionize the traditional air-compression technique. The La(Fe,Si)13-based materials are recognized as candidates with potential for practical applications. However, flexible strategies to improve the Curie temperature (TC) and further achieve the tunable giant magnetocaloric effect (GMCE) still need to be developed. Here, the systematic experimental investigation on a series of light elements (C, F, S) modified LaFe11.6Si1.4 compounds are presented. It is found that all modified samples exhibit a higher TC, with a negligible impact on the thermal hysteresis. The GMCE performance in C- and S-modified samples is significantly degraded, but the maximum magnetic entropy change |Δ sm| for the optimally doped F sample can be well maintained at 19.2 J kg−1 K−1 for a field change of 2 T. The preferential site occupancy of dopants is determined, and the microstructural observation and metastable atomic changes have also been analyzed. It is concluded that interstitial doping is more efficient to shift TC. The first-order transition can however not be maintained upon doping due to changes in the hybridization. These findings highlight the importance of the interplay between the lattice pressure effect and the covalent hybridization for this material family.

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 (ΔT_hys) and moderately steep ferromagnetic phase transition provides limitations 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 entropy change of the suction-casted sample shows a 67% improvement from 18.4 to 29.4 Jkg⁻¹K⁻¹ for a field change (∆μ₀H) of 5 T. As the thermal hysteresis has maintained a low ΔT_hys 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 ∆μ₀H = 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 significant 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 ΔT_hys.