Ferromagnetism in Lightly Doped Pr_1–xCa_xMnO₃ (x = 0.023, 0.036) Nanoparticles Synthesized by Microwave Irradiation

Abstract

Although the magnetic phase diagrams of bulk and thin film samples of Pr 1−x Ca x MnO 3 (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 Pr 0.977 Ca 0.023 MnO 3 and Pr 0.964 Ca 0.036 MnO 3 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 MnO 6 octahedra show considerable flattening (160.9°and 167.6°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 μ B /f.u. at 5 K, which is higher than the saturated Mn magnetic moment (3.8 μ B ). The enhanced magnetization is attributed to ordering of the Pr spins.

Efficient Dye Degradation Catalyzed by Manganese Oxide Nanoparticles and the Role of Cation Valence

“…e g orbital vacancy as in Mn 4+ results in too little interaction with the adsorbate which explains the least performing δ‐MnO 2 NPs where promotion of electron transfer to form the radicals required for MB degradation is slowed down. Unlike the present study, the maximum filling of the e g orbitals is always not beneficial for practical applications, for example trivalency of cations in metal oxides is useful for oxygen evolution reactions, and partial conversion of Mn 3+ to Mn 4+ ions facilitates ferromagnetic double exchange in rare‐earth doped manganites …”

In situ TEM analysis of resistive switching in manganite based thin-film heterostructures

“…47 Emergent ferromagnetism was indeed observed experimentally in nanoparticles of appropriate manganites. [48][49][50] Such metallic surface states could provide additional recombination channels contributing to the modied junction characteristics of our TEM-samples. The magnitude of the saturation current is only affected below L < 60 nm, where it eventually declines to the order of j s $ 10 3 Am À2 .…”

“…47 Emergent ferromagnetism was indeed observed experimentally in nanoparticles of appropriate manganites. [48][49][50] Such metallic surface states could provide additional recombination channels contributing to the modied junction characteristics of our TEM-samples.…”

An electrochemically reversible lattice with redox active A-sites of double perovskite oxide nanosheets to reinforce oxygen electrocatalysis

“…However, Rietveld renement of PXRD patterns shows the apparent reversibility of the oxygen content through changes in the unit cell volume (see Fig.S13 and Table S4 †). For example, aer 100 oxidation cycles, the unit cell volume increases by 0.3 A 3 while the c-axis decreases due to the distorted MnO 6 energy levels by the Jahn-Teller effect 41. Subsequent 100 reduction cycles decrease the cell volume by 0.4 A 3 and re-oxidation increases it again by 0.5 A 3 .…”