Models of Ni- and Co-ion occupation in LiNi0.5Co0.5PO4orthophosphate and its magnetic structure.

The neutron diffraction, magnetic and heat capacity measurements have been carried out to study the polycrystalline sample LiNi0.5Co0.5PO4prepared by the glycerol-nitrate synthesis method. Models of Ni- and Co-ion occupation the 4coctahedral position in a crystal structure LiNi0.5Co0.5PO4are calculated for a paramagnetic state. The best model is the Ni- and Co-ions occupy the 4csite inPnmapatent space-group in sequence Ni-Co-Ni-Co or Co-Ni-Co-Ni. It is shown that nickel ions formabplanes alternating with the planes of cobalt ions in the direction of theccrystallographic axis. At 7 K, an average magnetic moment of 3d-ions is equal to 1.90 (9)µB. The moments are ordering antiferromagnetically and parallel to thebcplane decreasing to zero at 15 K. In the high-spin state a temperature dependence of the Ni2+/Co2+ion-magnetic moment is well described within the 2D Ising model with order parameterß= 0.198 and Néel temperatureTN= 14.1 (1) K, obtained from heat capacity data. This temperature agrees well withTcr= 14.3 (2) K, determined with magnetic measurement. Maybe the short-range magnetic order exists in LiNi0.5Co0.5PO4over temperature region (14-16) K, that is confirmed by the maximum on a temperature dependence of the magnetization at 16.1 (5) K.

Magnetic and magneto-thermal properties of ferrimagnetic alloys (Er1-xYx)(Co0.84Fe0.16)2and their dependence on the orientations of resultant and sublattice magnetizations.

In this paper structure, magnetic and magneto-thermal properties: magnetic entropy change (ΔSm) and refrigeration capacity (q) of Er1-xYx(Co0.84Fe0.16)2alloys (x= 0, 0.2, 0.4, 0.6, 0.8, 1) in magnetic fields up to 90 kOe in a temperature range of 5-360 K are investigated. An analysis of temperature dependences of magnetization (σ) and high-field susceptibility (χhf) showed that in these compounds, three different ferri- and a one ferromagnetic structures are consequently realized. Concentration dependences of magnetic moment at 5 K (µf.u.), Curie temperature (TC), residual magnetization (σr) and coercivity (Hc) have been shown to have an extreme at intermediate Y concentration. The character of temperature dependence of magnetic entropy change (ΔSm(T)) depends on the composition and originates from the type of magnetic structure of the compound and the mutual orientation of R- and 3d- element sublattices magnetization with respect to the resulting one. In compounds withx= 0.6 andx= 0.8 temperature regions with different signs of ΔSmare observed, reflecting the change of dominating R- or 3d- sublattice in the resulting magnetization.