Mixed-valence La0.80(Ag1-xSrx)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(Ag1-xSrx)(0.20)MnO3 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, (mu o)Delta H = 5.0 T) were observed for the x = 0.25 manganite, while for the x = 0.50 sample interesting refrigerant capacity (129 J/kg, (mu o)Delta H = 2.0 T) and a wide interval of temperature at the full-width at half maximum delta T-FWHM of the magnetic entropy change curve were recorded (101 K, (mu o)Delta H = 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.