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.
New magnetic phenomena in TbNi2
Structural investigations at room temperature revealed that TbNi2 does not crystallize in the Laves phase structure, but shows a superstructure of the Laves phase with the space group F-43m. Susceptibility, specific heat, magnetostriction and magnetoresistance measurements on polycrystalline specimens showed an additional magnetic phase transition at TR = 14 K below the Curie temperature of TC = 36±0.2 K. In order to clarify the nature of this magnetic phase transition at 14 K, elastic neutron diffraction below and above TR and TC was performed. The analysis of these data showed that this transition at TR is due to the rotation of the Tb moments on three of the total of eight non-equivalent Tb sites in the rhombohedrally distorted unit cell in the magnetic ordered state. This rotation of these Tb moments is out of the [111] direction into a plane perpendicular to the space diagonal. The cause for this magnetic instability is due to an interplay of the regularly arranged vacancies in the superstructure and the crystal field level position which has been studied by inelastic neutron scattering.
On the magnetic behaviour of ACo2 (A = Y, Lu, Zr, Sc and Hf) compounds
Abstract The magnetic properties of ACo2 (A = Y, Lu, Zr, Sc, Hf) compounds were investigated in the temperature range 2–1100 K and fields up to 70 kOe. In order to avoid a possible alteration of the magnetic susceptibilities, χ, caused by the presence of magnetic ordered impurities, the χ values were obtained from magnetization isotherms, by extrapolation to H-1→0. At high temperatures, the ACo2 (A = Y, Lu, Sc and Hf) compounds show temperature dependences of magnetic susceptibilities of Curie-Weiss type. In ZrCo2, a more complex thermal variation of magnetic susceptibility is evidenced. At T ⪅ 15 K, the χ values for YCo2 and LuCo2 vary according to the relation χ = χ0(1 + aT2). The experimental data are analysed in the spin fluctuations model.