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The magnetic properties and magnetocaloric effect of ferromagnetic NdCo 2 compound have been investigated around the magnetic phase transition using magnetic and heat capacity measurements. The thermomagnetic irreversibility between the zero field-cooled and field-cooled magnetization curves is detected below Curie temperature in the low magnetic field, and it is attributed to the domain wall pinning effect. The maximum magnetic entropy change (∆S M ) of 7.33 Jkg −1 K −1 and large relative cooling capacity of 529.96 Jkg −1 was obtained over the wide working temperature range of 78 K under magnetic field change of 5 T. The corresponding maximum adiabatic temperature change (∆T ad ) is evaluated to be 3.1 K under a same magnetic field change. Meanwhile, negligible thermal and magnetic hysteresis loss was observed in paramagnetic (PM) to ferromagnetic (FM) transition region. Such a magnetocaloric effect is attributed to a second-order magnetostructural transition from a PM cubic phase to a FM tetragonal phase around the Curie temperature of T c ≈ 102 K. The observed magnetocaloric performance is comparable or even better than some earlier reported rare-earth based Laves compounds under the same magnetic field change, implying that the NdCo 2 is one of the potential refrigerant material working at low temperature. The critical exponent analysis was carried out to understand the nature and underlying mechanism of the PM to FM phase transition. The critical exponents (β, γ) obtained from modified Arrott plots, the Kouvel-Fisher plot, and the critical isotherm are consistent with each other and obey the Widom scaling relation (δ = 1+γ/β). The values of critical exponents suggest that the NdCo 2 belongs to the three-dimensional-Ising model with short-range interaction. The present results may give some clues for searching novel materials with excellent magnetocaloric performance for refrigeration technology.

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The crystal structures and phase relationships of Tb 1−x Dy x Co 2 alloys with 0 ⩽ x ⩽ 1 were investigated by synchrotron-based high-resolution x-ray powder diffraction. Three different crystal structures are observed in the system: all the compositions show cubic structure with space group Fd 3m at temperatures above the Curie temperature T C; the Tb-rich side sample shows a rhombohedral structure with space group R 3m and the Dy-rich side sample has a tetragonal I4 1 /amd space group. In situ measurements on the intermediate compound Tb 0.3 Dy 0.7 Co 2 show a rhombohedral to tetragonal structural transition, and the two phases coexist from 99 K to 111 K, where the so-called magnetic morphotropic phase boundary (MPB) is found. The coexisting phases are believed to induce the anomalous magnetostrictive effect in the MPB regime.