Abstract
Nd2Fe17−xCox (x=0,1,2,3,4) intermetallic compounds, obtained under arc-melting conditions, have been investigated by means of X-ray diffraction analysis (XRD), Mössbauer spectrometry and magnetic measurements. The Rietveld refinement revealed that the sample is a pure compound with rhombohedral Th2Zn17-type structure (R3¯m space group) with the following lattice parameters: a = 8.5792 (2)Å, c = 12.4615 (2)Å. Using Mössbauer spectrometry analysis coupled with structural consideration we have unambiguously determined the cobalt atoms preferred inequivalent crystallographic site. Nd2Fe17 show an increase of 3.5T in their weighted average hyperfine fields upon cobalt substitution. Whatever the cobalt content, the hyperfine field of these compounds follow this sequence Hhf{6c}>Hhf{9d}>Hhf{18f}>Hhf{18h}. The magnetic measurements showed that the Curie temperature increases with the Co content. The magnetic entropy change (ΔSM) was estimated from isothermal magnetization curves and it increases from 3.35J/KgK for x=0 to 5.83J/KgK for x=2 at μ0H=1.6T. The relative cooling power (RCP) is in the range of 11.6J/kg (x=0) and 16J/kg (x=2).
Crystal structure of the rhombohedral R3¯m Nd2Fe17 compound (right). Room temperature Mössbauer spectra of Nd2Fe17 (up) and Nd2Fe13Co2 (down) compounds (middle). 3D surface plots showing ΔS in terms of temperature and the applied magnetic field for Nd2Fe15Co2 (right). [Display omitted]