Abstract
The single-phase intermetallic compounds GdFe12−xCrx (x = 2, 2.5 and 3), elaborated by arc-melting method and annealed at 1073 K, crystallize in the ThMn12-type structure with the I4/mmm space group. The structural, magnetic and magnetocaloric properties of these intermetallic compounds were studied extensively by means of X-ray powder diffraction (XRD), Mössbauer spectrometry and magnetic measurements. The Rietveld analysis of X-ray diffraction patterns reveals that the lattice parameters of GdFe12−xCrx (x = 2, 2.5 and 3) compounds increase linearly with increasing Cr content up to x = 3, and proves that Cr atom prefers 8i sites in the ThMn12 structure and that Fe occupies 8i, 8f and 8j. The Mössbauer spectra study based on the Wigner-Seitz cell volumes correlation with the isomer shift parameter of each specific site 8i, 8f and 8j, confirms the preferred inequivalent crystallographic site of Cr atoms. Ab initio calculations of GdFe12−xCrx were performed using the density functional theory (DFT) based on the full potential linearized augmented plane wave (FLAPW). The calculated data are in good agreement with the results of the magnetic measurements as well as with the Mössbauer spectrometry. The variation of magnetization (M) vs. temperature (T) reveals that all compounds exhibit a second-order ferromagnetic to paramagnetic phase transition in the vicinity of the Curie temperature (TC). The substitution of Fe by Cr yields enhancement of the magnetic ordering transition temperature. The maximum magnetic entropy change (ΔSM) was estimated from isothermal magnetization curves and it increases from 1.82 J/kg.K for x = 2, to 2.95 J/kg.K for x = 3, under a field change of 1.5 T. The relative cooling power (RCP) is in the range of 12.5 J/kg for x = 2 and 30.4 J/kg for x = 3. Our results suggest that such substituted compounds could be considered as a potential candidate for magnetic refrigeration technology.
Schematic representation of the relationship between CaCu5 (along [001] axis) and ThMn12 (along [010] axis) structures (a), illustration of atomic arrangements in GdFe10Cr2 crystal structure along [010] axis (b), and the tetragonal I4/mmm crystal structure of GdFe10Cr2 (c). [Display omitted]
•GdFe12¡xCrx (x = 2, 2.5 and 3) samples prepared by arc melting subsequent annealing.•Magnetocaloric effect at low field of GdFe12¡xCrx (x = 2, 2.5 and 3) was studied for the first time.•The Rietveld analysis indicates that Cr atoms substitute iron in the site 8i.•This result is corroborated by Mössbauer study and DFT calculations.•A good agreement obtained between first-principle calculations and measured magnetic and hyperfine parameters.