Magnetocaloric effect in La0.70Ag0.25MnO3+δ magnetic nanoparticles

Experimental study of magnetocaloric effect (MCE) was performed by direct and indirect methods on La0.70Ag0.25MnO3+δ nanoparticles with rhombohedral LaAlO3 – type crystal structure (R3¯c space group – No. 167, hP30). The content of oxygen was modified by annealing at 800 °C/48h in different atmosphere (air, O2 and Ar). The Curie temperature TC increases from 250 K to 319.5 K and to 322.9 K with the content of oxygen. The adiabatic temperature change ΔT(4T) = 1.52 K, the change of magnetic entropy −ΔSmax(4T) = 3.96 Jkg−1K−1 and the relative cooling power RCT(4T) = 172 J/kg are maximal for sample treated in Ar and decrease with oxygen content. The frequency dependence of ΔT (f) and the shape of maximum in ΔT (T) and −ΔSmax (T) indicate relaxation processes and presence of magnetic inhomogeneities which are present mostly in sample treated in Ar. The samples demonstrate the stability of the MCE up to 1000 cycles of switching on and off the magnetic field without any signs of degradation. •Tuning of MCE in La0.7Ag0.25MnO3+δ by heat treatment and off stoichiometry.•Impact of oxygen content on magnetocaloric effect and the Curie temperature.•Comparisson of undirect and direct MCE measurements.•Low-frequency relaxation processes indicated from direct measurements of MCE.