Magnetocaloric effect, heat capacity and exchange interactions in nonstoichiometric Er0.65Gd0.35Co2Mnx compounds

Abstract

The crystal structure, magnetic and magnetothermal properties of nonstoichiometric Er0.35Gd0.65Co2Mnx (0 ≤ x ≤ 0.4) compounds have been investigated. It is observed a considerable increase in the Curie temperature from TC = 170 K up to above room temperature TC = 324 K with increasing the Mn content. The exchange interactions in nonstoichiometric alloys of the RCo2Mnx - type (R is Er, Er0.35Gd0.65 and Tb) are determined within a two-sublattice mean field model. It is shown that increase in the Curie temperature of the RCo2Mnx-type nonstoichiometric alloys is associated with increasing of the magnetic moment and strengthening exchange interactions in the 3d-sublattice. The magnetization and heat capacity measurements were used to estimate the magnetocaloric effect in the compounds for the magnetic field change ΔH ≈ 20 kOe. It was found that compounds exhibit plateau-like temperature dependence of the field induced magnetic entropy change ΔSm over a wide temperature range from 50 to 350 K and high values of Relative Cooling Power (up to 235 J/kg), the full width at half maximum of ΔSm (ΔTFWHM up to 310 K) and refrigerant capacity (RC up to 196 J/kg). The calculated and directly measured temperature variation of the adiabatic temperature change ΔТ are found to be similar.