Structural, microstructural and magnetic properties of (La(1-x)Ca(x))MnO3 nanoparticles

Research Progress in Rare Earth-Doped Perovskite Manganite Oxide Nanostructures

Perovskite manganites exhibit a broad range of structural, electronic, and magnetic properties, which are widely investigated since the discovery of the colossal magnetoresistance effect in 1994. As compared to the parent perovskite manganite oxides, rare earth-doped perovskite manganite oxides with a chemical composition of LnxA1-xMnO3 (where Ln represents rare earth metal elements such as La, Pr, Nd, A is divalent alkaline earth metal elements such as Ca, Sr, Ba) exhibit much diverse electrical properties due to that the rare earth doping leads to a change of valence states of manganese which plays a core role in the transport properties. There is not only the technological importance but also the need to understand the fundamental mechanisms behind the unusual magnetic and transport properties that attract enormous attention. Nowadays, with the rapid development of electronic devices toward integration and miniaturization, the feature sizes of the microelectronic devices based on rare earth-doped perovskite manganite are down-scaled into nanoscale dimensions. At nanoscale, various finite size effects in rare earth-doped perovskite manganite oxide nanostructures will lead to more interesting novel properties of this system. In recent years, much progress has been achieved on the rare earth-doped perovskite manganite oxide nanostructures after considerable experimental and theoretical efforts. This paper gives an overview of the state of art in the studies on the fabrication, structural characterization, physical properties, and functional applications of rare earth-doped perovskite manganite oxide nanostructures. Our review first starts with the short introduction of the research histories and the remarkable discoveries in the rare earth-doped perovskite manganites. In the second part, different methods for fabricating rare earth-doped perovskite manganite oxide nanostructures are summarized. Next, structural characterization and multifunctional properties of the rare earth-doped perovskite manganite oxide nanostructures are in-depth reviewed. In the following, potential applications of rare earth-doped perovskite manganite oxide nanostructures in the fields of magnetic memory devices and magnetic sensors, spintronic devices, solid oxide fuel cells, magnetic refrigeration, biomedicine, and catalysts are highlighted. Finally, this review concludes with some perspectives and challenges for the future researches of rare earth-doped perovskite manganite oxide nanostructures.

Microstructural, Magnetic, and Optical Properties of Pr-Doped Perovskite Manganite La0.67Ca0.33MnO3 Nanoparticles Synthesized via Sol-Gel Process

We report on microstructural, magnetic, and optical properties of Pr-doped perovskite manganite (La_1 - xPr_x)_0.67Ca_0.33MnO₃ (LPCMO, x = 0.0-0.5) nanoparticles synthesized via sol-gel process. Structural characterizations (X-ray and electron diffraction patterns, (high resolution) TEM images) provide information regarding the phase formation and the single-crystalline nature of the LPCMO systems. X-ray and electron diffraction patterns reveal that all the LPCMO samples crystallize in perovskite crystallography with an orthorhombic structure (Pnma space group), where the MnO₆ octahedron is elongated along the b axis due to the Jahn-Teller effect. That is confirmed by Raman spectra. Crystallite sizes and grain sizes were calculated from XRD and TEM respectively, and the lattice fringes resolved in the high-resolution TEM images of individual LPCMO nanoparticle confirmed its single-crystalline nature. FTIR spectra identify the characteristic Mn-O bond stretching vibration mode near 600 cm^- 1, which shifts towards high wavenumbers with increasing post-annealing temperature or Pr-doping concentration, resulting in further distortion of the MnO₆ octahedron. XPS revealed dual oxidation states of Mn³⁺ and Mn⁴⁺ in the LPCMO nanoparticles. UV-vis absorption spectra confirm the semiconducting nature of the LPCMO nanoparticles with optical bandgaps of 2.55-2.71 eV. Magnetic measurements as a function of temperature and magnetic field at field cooling and zero-field cooling modes, provided a Curie temperature around 230 K, saturation magnetization of about 81 emu/g, and coercive field of 390 Oe at 10 K. Such magnetic properties and the semiconducting nature of the LPCMO nanoparticles will make them as suitable candidate for magnetic semiconductor spintronics.