Magnetocaloric properties of Fe-substituted La–Sr-manganites

Abstract

The effect of Fe doping on the structural, magnetic and magnetocaloric properties was studied on La1-xSrxMn1-yFeyO3 (x = 0.10, 0.20; y = 0.00, 0.10, 0.15) manganites prepared by solid state reaction method. X-ray structural analysis showed that the substitution of manganese by iron does not change the phase state in the rhombohedral series (x = 0.20). In the orthorhombic series (x = 0.1), the substitution of manganese by iron leads to a phase transition from the Jahn-Teller O′ phase to the ordinary O phase. We explain this transition by a decrease in the concentration of Mn3+ ions, which are Jahn-Teller centers. In addition, we recorded an increase in the unit cell parameters in the iron-containing samples of both series. We explain this effect by the presence of a certain amount of Fe4+ ions. Magnetic measurements showed that all samples undergo a second order FM–PM transition at the Curie temperature (Tc). The Curie temperature TC and the Curie-Weiss temperature (Θ) decrease with increasing Fe content. The relationship between the variation of TC and structural parameters the Me–O bond length and the bond angle of Me–O–Me with increasing Fe content has been established. In the paramagnetic temperature range, the formation of magnetic clusters was suggested from isothermal magnetization data. For a magnetic field variation of 5 T, the entropy change is evaluated.