Magnetocaloric effect in La0.70Ag0.25MnO3+8magnetic nanoparticles

Experimental study of magnetocaloric effect (MCE) was performed by direct and indirect methods on La0.70Ag0.25MnO3+delta nanoparticles with rhombohedral LaAlO3 - type crystal structure (R space group - No. 167, hP30). The content of oxygen was modified by annealing at 800 ?C/48h in different atmosphere (air, O-2 and Ar). The Curie temperature T-C increases from 250 K to 319.5 K and to 322.9 K with the content of oxygen. The adiabatic temperature change delta T(4T) = 1.52 K, the change of magnetic entropy -delta S-max(4T) = 3.96 Jkg(-1)K(-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 delta T(f & nbsp;)and the shape of maximum in delta T (T) and -delta S-max(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.