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The single-layer Ta(20 nm)Nd13Fe77B10(100 nm)Ta(20 nm) film was prepared and diffusion-processed by Nd25Cu75(20 nm) and Nd70Cu30(20 nm). The evolutions of microstructure and magnetic properties were comparably studied. By using same amount of diffusion layer, different coercivities were achieved. The coercivity enhancement mechanism was explained phenomenologically by surface defects of Nd2Fe14B grains and estimation of activation volume. It was found that due to the increased Nd composition in grain boundaries, the activation volume was reduced and the local anisotropy was enhanced due to the remedied surface defect. Such dependence was consistent with the coercivity changes.

As the emerging ambient low-cost magnetic refrigeration system, the substitution effects on the magnetic properties and magnetocaloric effects in Al1−xSixFe2B2 (x = 0, 0.1, 0.2, 0.3) and Al1−yGayFe2B2 (y = 0.1 and 0.2) have been studied. The single phase is formed in a wide substitution composition region. All phase transitions in these compounds are of second-order and their Curie temperature (Tc) increases with more Si and Ga substitutions. For a field change of 5 T and 7 T, the maximum of entropy change (ΔSmax) of 4.9 J Kg−1 K−1 and 6.3 J Kg−1 K−1 are obtained and not dependent on the Si substitution amount in Al1−xSixFe2B2. As comparison, by Ga substitution, for the field change of 7 T and 5 T, the ΔSmax have been increased to 7.5 J Kg−1 K−1 and 6 J Kg−1 K−1 respectively. The tunable ambient Tc and considerable ΔSmax suggest that AlFe2B2-based compounds are potential low-cost ambient magnetic refrigeration candidates.

High-purity RAl3C3 phases (R = Nd, Gd, Tb, Dy, Ho, Er and Tm) have been synthesized and all crystallized in hexagonal structure with the space group (#194) P63/mmc. Lattice parameters are decreased from R = Nd to R = Tm due to lanthanide contraction. Two nonlinear antiferromagnetic states are found in NdAl3C3 phase. While simple ferromagnetic state is observed for R = Gd, Tb, Ho and Er cases. A high coercivity of 0.45 T has been achieved in TbAl3C3 phase at 4 K indicating the uniaxial magnetocrystalline anisotropy. Before entering into paramagnetic state, DyAl3C3 phase undergoes the complex magnetic phase transition with increasing temperature. All these phase transitions are of second-order due to nonhysteresis.

By hetero-structural alloying ferromagnetic hexagonal Ho2In with antiferromagnetic orthorhombic Ho2Al, the magnetic and structural changes have been observed in Ho2In1-xAlx (0 ≤ x ≤ 0.4) alloys. At the critical composition x = 0.1, the highest maxima of magnetic entropy change of 16.3 Jkg-1K−1 and the adiabatic temperature change of 6.5 K have been obtained via an unconventional hysteresis-free metamagnetic phase transitionm, which is higher than 9 Jkg-1K−1 and 5.4 K in Ho2In benchmark alloy undergoing second-order phase transition. Such increment is associated with the intensified magnetoelastic coupling. The deeper origin is proposed to be from the delocalized 5d electrons of rare-earth atoms by external field since the magnetoresistence is also maximized at the critical composition. The hetero-structural alloying strategy is demonstrated to be effective to intensify the MCE effect without causing the undesirable hysteresis.

The tetragonal Cu 2 Sb-type Mn 1.8 Cu 0.2 Sb alloy was prepared by solidification under zero field and high magnetic field of 12 T. No thermal hysteresis was observed. High-magnetic-field (HMF) solidification led into c -axis texture in Mn 1.8 Cu 0.2 Sb alloy. Moreover, the severity of metamagnetic transformation in a Mn 1.8 Cu 0.2 Sb alloy was steepened and the resultant magnetic entropy change was enhanced. The exchange bias at low temperature was observed. Our work demonstrated the pronounced influences of HMF solidification on the crystallographic orientation, metamagnetic phase transformation and the magnetic exchange couplings.

By gradually substituting Al for In in Gd2In1−xAlx (0.4 ≤ x ≤ 1) system, the hexagonal structure for Gd2In1−xAlx (x ≤ 0.6) is gradually evolved into orthorhombic one for x ≥ 0.7. The phase transition temperature is monotonously decreased. At the critical composition of x = 0.7, the second-order phase transformation in hexagonal Gd2In1−xAlx (x ≤ 0.6) is evolved into the first-order-like metamagnetic one without conventional hysteresis in orthorhombic Gd2In1−xAlx (x ≥ 0.7), leading into the enhanced magnetic entropy change and adiabatic temperature change. A lambda-like anomaly on the Cp-T curves is also caused. Due to being close to the phase borderline separating hexagonal and orthorhombic structure, such enhanced magnetocaloric effect is considered to be from the greatly distorted lattice.

The effects of Ta substitution on the phase transition have been studied in Hf1-xTaxFe1.98 (x = 0.125, 0.13, 0.135) alloys with kagome-type lattice. Increased Ta substitution leads into the reduced metamagnetic transition temperature (Tt). The nature of such phase transition is also changed from second-order type to the weak first-order one, suggested by the gradually observed hysteresis. The magnetic entropy change (ΔS) is meanwhile enhanced from 3.04 J kg−1 K−1 to 3.4 J kg−1 K−1. Such enhanced magnetocaloric effects are strongly correlated with the enhanced magneto-elastic effect, which is further confirmed by the maximized saturation magnetostriction (λs//) of ~1700 ppm near the Tt of Hf0.865Ta0.135Fe1.98 alloy. The concurrence of maximized ΔSmax and λs// suggests the strong magneto-elastic coupling during phase transition and the high linear co-efficiency of negative thermal expansion can be triggered in Fe-deficient Hf0.865Ta0.135Fe1.98 alloy.