Effects of rare earth ions substitution on the magnetocaloric and critical behavior of La0.6A0.2Sr0.2MnO3 (A=Pr, Nd, Ce) manganite

We have studied the influence of Ce, Pr and Nd elements substitution on the magnetic and magnetocaloric properties of La0.6A0.2Sr0.2MnO3 (A = Pr, Nd, Ce) polycrystalline manganites. X-ray diffraction patterns show that the samples crystallize in the rhombohedral structure with R-3C space group. The Pr and Nd doped samples are single phase, while Ce doped sample has a CeO2 secondary phase. The temperature dependent magnetization exhibits a sharp paramagnetic (PM)-ferromagnetic (FM) transition at 333, 252 and 243 K for Ce, Pr and Nd doped samples, respectively. The results show that the saturation magnetization of the pure and Nd doped samples are higher than Pr doped sample, while the Ce doped sample exhibits lowest magnetization. The magnetic entropy change (ΔSM) was calculated by applying the Maxwell equation and the estimated values in H = 25 kOe were found to be 3.20, 2.63, 3.34 and 3.50 J/kgK for pure, Pr, Nd and Ce doped samples, respectively. Also, improved relative cooling power was observed for the Pr and Nd doped samples. By using three different methods including analyzing magnetization data using Banerjee's criterion, normalizing entropy change versus reduced temperature and using ΔSM(T) data which is related to the local exponent (nL), it is found that all samples display a second-order magnetic phase transition. The critical exponents of the second-order magnetic phase transition for the samples has been calculated, using scaling law and Widom scaling relation and their reliability has also been confirmed with the scaling hypothesis.