Ferromagnetism in Lightly Doped Pr1-xCaxMnO3 (x=0.023, 0.036) Nanoparticles Synthesized by Microwave Irradiation

Although the magnetic phase diagrams of bulk and thin film samples of Pr1-xCaxMnO3 (x <= 0.5) are widely explored, few works have been published on the magnetic properties of nanoparticles, especially in the lightly, doped regime. In this paper, microwave irradiation was used to synthesize the Pr0.977Ca0.023MnO3 and Pr0.964Ca0.036MnO3 Manganite phases with Pnma space group in the form of anisotropic nanoparticles. The phase identification, structural characteristics, and formation of the nanostructures were analyzed by Rietveld analysis of the X-ray diffraction patterns, electron microscopy, and combining thermal analysis with infrared spectroscopy, respectively. Transport measurements on the annealed samples revealed the insulating nature, and electrical conduction occurs through thermally activated hopping of small polarons. The Mn-O-c-Mn tilt angles in the MnO6 octahedra show considerable flattening (160.9 degrees and 167.6 degrees for x = 0.023 and x = 0.036, respectively), possibly enhancing the electronic double exchange and promoting ferromagnetism. Ferromagnetic ordering of Mn spins was indeed observed below 109 K, and interestingly, the magnetic moment for x = 0.036 was 3.92 mu(B)/f.u. at 5 K, which is higher than the saturated Mn magnetic moment (3.8 mu(B)). The enhanced magnetization is attributed to ordering of the Pr spins.