The effect of high energy ball milling on the structural, magnetic and magnetocaloric properties of Ni50Mn36Sn14 Heusler-type alloy has been studied. X-ray diffraction results have revealed a reduction in the crystalline grain size concomitantly with defect inclusions in the crystalline lattice, favouring a chemical disorder effect that transforms the L21–B2-type disordered structure to a simple cubic B2-type structure for increasing milling time. From magnetometry and Mössbauer spectroscopy results, a decrease in the ferromagnetic exchange interaction contribution, an enhancement of the effective exchange bias field and a significant reduction in the magnetic entropy change of the milled alloy are observed.

Localization and magnetism of Fe replacing either Mn or Ni in the Ni2Mn1.44Sn0.56-type Heusler alloy have been systematically investigated using magnetization, scanning electron microscopy and Mössbauer spectroscopy. It has been shown that the addition of Fe either in Mn or in Ni sites reduces the fraction of the Mn-rich NiMnSn-type Heusler alloys that has short-range antiferromagnetic interactions; consequently it reduces the martensitic–austenitic transition temperature and increases the thermal hysteresis width due to an increase in atomic disorder caused by Fe replacements. The Fe atoms in Mn sites have two magnetic configurations with magnetic moments of 0.8μB/Fe and 1.4μB/Fe in the martensitic orthorhombic structure, while Fe in Ni sites have magnetic moments smaller than 0.1μB/Fe. These results indicate that the Fe atoms are distinctly substituting either Mn or Ni and the decrease in the martensitic phase transition temperature for increasing Fe content can be mainly attributed to the Fe atoms in the Mn sites in both cases.

The mechanosynthesis process has been applied in theLaFe11.4Si1.6 compound to reduce the undesirable segregated rich-Fe phases that impair its application as a solid magnetic refrigerant. The influence of La substitution (5 at. %) by Y or Gd atoms on the magnetic and magnetocaloric properties has been also studied. Y- and Gd-substituted compounds have a magnetic ordering temperature higher than the pure La compound. While the Y-substituted compound keeps a first-order-like magnetic transition feature, the Gd-substituted one seems to suppress it. The maximum value of the magnetic entropy change of the Y compound is roughly the same as the La compound (−18 J∕kg K) but with a magnetic entropy change peak significantly broader. For the Gd-compound case a drastic reduction of the magnetic entropy change (−7 J∕kg K) is found.

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The influence of the chemical pressure on the magneto-structural properties of the Ni2MnGa Heusler alloy after a gradual substitution of Ga by Sn atoms was theoretical and experimentally studied in this work. Our data clearly show that an expansion of the L21-cell volume due Sn-substitution causes a diminution of the internal structural stress and favors the austenitic state in low temperatures where martensitic phase should prevail. It is also shown that the total magnetization reduces with increasing Sn-content, a behavior explained by a reduction of the Ni-magnetic moment, since an increase of Mn-magnetic moment was theoretically calculated. The Sn-substitution effect in the Ni2MnGa compound is similar to that found in experiments performed under high applied magnetic fields, which means that in both cases there is an increase of the L21 cell-volume favoring the austenitic state in low temperatures. Magnetization values in martensitic state of the pure Ga-compound systematically reduce after consecutive M(T) thermal cycle recorded at 5 mT; an effect not yet reported within our knowledge and attributed here to modifications in local magnetic anisotropies during the field cycles.