Structural, magnetic and thermal properties of intermetallics Nd3Fe27−xCoxV2 (x = 0, 2 and 4) and their hydrides

Intermetallics of the Nd3Fe27−xCoxV2 (x = 0, 2 and 4) system with monoclinic type structure and their hydrides were prepared by arc melting and exposed to hydrogenation. The effects of Co substitution of Fe on the magnetic hyperfine fields of intermetallic compound Nd3Fe27V2, as well as the effects of interstitial hydrogen additions on the symmetry and local magnetic properties in these systems were studied. The investigations were performed by powder X-ray diffraction, Mössbauer spectroscopy and simultaneous TGA-DSC. Both site populations and magnetic hyperfine field strength were analyzed in order to discriminate between the Co and H contributions to the local atomic environments in these systems. The values of magnetic hyperfine fields corresponding to inequivalent lattice sites were found to be enhanced after the increase in Co content and hydrogenation. Slight changes in the relative site occupancies were observed. Simultaneous TGA-DSC studies showed that the amount of hydrogen insertion decreased slightly with the increase of Co contents, while the enthalpy associated with hydrogen desorption decreased sharply under heat treatment. The Nd3Fe27−xCoxV2 (x = 0, 2 and 4) and their hydrides are not stable under treatment and two exothermic peaks are observed in the DSC curves, corresponding to the decomposition of the monoclinic phase with the precipitation of α-Fe phase.