Structural, magnetic and magnetocaloric properties of La0.65Ca0.35−xNaxMnO3 Na-doped manganites

In this work, we report the effect of Na doping on the structural, magnetic and magnetocaloric properties in La0.65Ca0.35−xNaxMnO3 powder samples. Our samples have been synthesized by the solid-state reaction method at high temperature. The parent compound La0.65Ca0.35MnO3 crystallizes in the orthorhombic system with a Pbnm space group. Na doping induces a structural transition from orthorhombic (Pbnm) to rhombohedral (R3¯c) symmetry. With increasing Na amount, the unit cell volume decreases in the orthorhombic phase (x⩽0.1) and increases in the rhombohedral one. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our investigated samples display a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature TC increases with increasing Na content from 248 K for x=0–315 K for x=0.2. The critical exponent γ   defined by Msp(T)=Msp(0)[1-T/TC]γMsp(T)=Msp(0)[1-T/TC]γdeduced from the magnetization measurements as a function of the magnetic field up to 7 T at several temperatures is found to be 0.34 for x  =0.1. A large magnetocaloric effect has been observed in all samples, the maximum entropy change, |ΔSm|max|ΔSm|max, shifts to higher values with increasing Na content. |ΔSm|max|ΔSm|max reaches the highest value of 3 and 5.8 J/Kg K for a magnetic field change of 5 T for x=0.05 and 0.2.