Magnetic phase transition and Mossbauer spectroscopy of ErNi2Mnx compounds
Investigation of ErNi2Mnx with 0.90 ≤ x ≤ 1.10 indicates that the MgCu2-type structure (with space group Fd-3m) is formed within x = 0.97−1.10. Curie temperature TC = 50 K of ErNi2Mn is significantly higher than those of the corresponding ErNi2 (TC = 7 K) and ErMn2 (TC = 15 K) compounds. Detailed analyses of DC magnetization data demonstrate that the magnetic phase transition at the Curie temperature is second order. The magnetic entropy change around TC has been found to be 4.8 J/kg K for a magnetic field change of 0 to 5 T with its relative cooling power ∼283 J/kg. 57Fe Mossbauer spectra below TC have been fitted with three sub-spectra representing three inequivalent local magnetic environments while the paramagnetic spectra are fitted using two sub-spectra for two inequivalent crystal sites (8a and 16d), which supports the conclusion based on Rietveld refinement that Mn atoms occupy at both 8a and 16d sites.
Magnetic properties of the off-stoichiometric GdNi2Mnx alloys
Abstract The structure and magnetic properties of the off-stoichiometric GdNi 2 Mn x (0 ⩽  x  ⩽ 0.6) alloys have been studied. The alloys with 0  х 2 -type, whereas, starting from the composition х  ⩾ 0.4, in the samples there forms the PuNi 3 -type phase. Increase in the Mn content is found to lead to a considerable growth of the Curie temperature from 80 K for the binary GdNi 2 up to 190 K for the GdNi 2 Mn 0.4 alloy. Magnetization at 4 K decreases with increasing x , which indicates the formation of a ferrimagnetic structure. The magnetic entropy change has been determined from the temperature dependences of the magnetization using the Maxwell equation. For GdNi 2 Mn 0.4 , upon changing the magnetic field from 0 to 9 T, the isothermal entropy change in the vicinity of the Curie temperature has been found to be 4.6 J kg −1  K −1 . The results are discussed under assumption of growth of both the Ni magnetic moment and Gd–Mn and Ni–Mn exchange interactions with increasing the manganese content.
Magnetostriction of (rare earth) Ni2 intermetallic compounds
Abstract The magnetostriction, parallel and perpendicular to the applied magnetic field, has been measured for the RENi 2 intermetallic compounds (RE = Pr, Nd, Sm, Tb, Dy, Ho, Er and Tm), between 3.8 K and well above the Curie temperatures in polycrystalline samples. From the comparison with a theoretical analysis, the temperature dependence for the phenomenological magnetostriction parameters h 1 and h 2 has been extracted for the compounds SmNi 2 and NdNi 2 , in good agreement with the Callen and Callen I frbuilt:5/2 [ L −1 ( m )] law. An analysis within the crystal field (CEF) theory has allowed the determination of the single-ion magnetoelastic coupling parameters M ϵ 2 (for the tetragonal-distortion mode) and M ϵ 2 (for the rhombohedral mode) for the compounds TbNi 2 , DyNi 2 , HoNi 2 and ErNi 2 at the ordered regime. A relevant result is that the point charge model for the distorted CEF is reasonably well accomplished. Parastriction calculations in PrNi 2 , TbNi 2 and DyNi 2 seem to indicate the weakness of quadrupolar pair interactions.