Mixed-valence La_0.80(Ag_1−x Sr _x )_0.20MnO₃ manganites with magnetocaloric effect

We report the effect of the simultaneous inclusion of Ag¹⁺ and Sr²⁺ cations on the crystal structure and the magnetocaloric effect (MCE) of La_0.80(Ag_1−x Sr _x )_0.20MnO₃ manganites (x = 0.0, 0.25, 0.50, 0.75, 1.0) synthesized by the solid-state reaction method. X-ray photoelectron spectroscopy was used to verify chemical composition and the amount of Mn³⁺–Mn⁴⁺ cations, while the magnetic performance was evaluated by means of a Physical Property Measuring System. The progressive substitution of Ag¹⁺ by Sr²⁺ causes the increase of the number of Mn⁴⁺ cations, together with increasing ionic radii for the A-site contents up to x = 0.75, both favoring the enhancement of the double-exchange interaction and hence, the MCE. Excellent values of magnetic entropy change (−4.6 J/kg K, μ _oΔH = 5.0 T) were observed for the x = 0.25 manganite, while for the x = 0.50 sample interesting refrigerant capacity (129 J/kg, μ _oΔH = 2.0 T) and a wide interval of temperature at the full-width at half maximum δT _FWHM of the magnetic entropy change curve were recorded (101 K, μ _oΔH = 2.0 T) caused by two successive magnetic transitions. Magnetic performance was explained in terms of the effect of the cation substitution on the double-exchange interaction and the tolerance factor.