Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Detailed magnetization measurements in La_{5/8-y}Pr_{y}Ca_{3/8} MnO_{3}, including magnetic relaxation properties, demonstrate the dynamic nature of the phase separated state in manganites. The difference between the field-cooled-cooling and zero-field-cooled magnetization curves signals the existence in the latter of blocked metastable states separated by high energy barriers. Results of the magnetic viscosity show that the system becomes unblocked in a certain temperature window, where large relaxation rates are observed. We propose a simple phenomenological model in which the system evolves through a hierarchy of energy barriers, which separates the coexisting phases. The calculated magnetization curves using this model reproduce all the qualitative features of the experimental data. The overall results allowed us to construct an H-T phase diagram, where frozen and dynamical phase separation regions are clearly distinguished.

Dynamic phase separation in La_{5/8-y}Pr_{y}Ca_{3/8}MnO_{3}

Recent experiments showed that the robust charge-ordering in manganites can be weakened by reducing the grain size down to nanoscale. Weak ferromagnetism was evidenced in both nanoparticles and nanowires of charge-ordered manganites. To explain these observations, a phenomenological model based on surface phase separation is proposed. The relaxation of superexchange interaction on the surface layer allows formation of a ferromagnetic shell, whose thickness increases with decreasing grain size. Possible exchange bias and softening of the ferromagnetic transition in nanosized charge-ordered manganites are predicted.

Surface phase separation in nanosized charge-ordered manganites

Structure and luminescence investigation of Gd3+-sensitized perovskite CaLa4Ti4O15:Eu3+: A novel red-emitting phosphor for high-performance white light-emitting diodes and plants lighting.

The continuous miniaturization of the charge-based electronic devices and overcoming the bottleneck of Moore's law, have driven the rapid growth of spintronics, which operates the freedom of electronic spin rather...

Half-metallic double perovskite oxides: recent developments and future perspectives

Structural characterization, magnetic and optical properties of perovskite (La1−xLnx)0.67Ca0.33MnO3 (Ln = Nd and Sm; x = 0.0–0.5) nanoparticles synthesized via the sol-gel process

Recently, double perovskite (DP) oxides denoted A2B′B″O6 (A being divalent or trivalent metals, B′ and B″ being heterovalent transition metals) have been attracting much attention owing to their wide range of electrical and magnetic properties. Among them, rhenium (Re)-based DP oxides such as A2FeReO6 (A = Ba, Sr, Ca) are a particularly intriguing class due to their high magnetic Curie temperatures, metallic-like, half-metallic, or insulating behaviors, and large carrier spin polarizations. In addition, the Re-based DP compounds with heterovalent transition metals B′ and B″ occupying B sites have a potential to exhibit rich electronic structures and complex magnetic structures owing to the strong interplays between strongly localized 3d electrons and more delocalized 5d electrons with strong spin–orbit coupling. Thus, the involved physics in the Re-based DP compounds is much richer than expected. Therefore, there are many issues related to the couplings among the charge, spin, and orbitals, which need to be addressed in the Re-based DP compounds. In the past decade, much effort has been made to synthesize Re-based DP compounds and to investigate their crystal structures, structural chemistry, and metal–insulator transitions via orbital ordering, cationic ordering, and electrical, magnetic, and magneto-transport properties, leading to rich literature in the experimental and theoretical investigations. This Review focuses on recent advances in Re-based DP oxides, which include their synthesis methods, physical and structural characterizations, and advanced applications of Re-based DP oxides. Theoretical investigations of the electronic and structural aspects of Re-based DP oxides are also summarized. Finally, future perspectives of Re-based DP oxides are also addressed.

/pdf/recent-advances-in-re-based-double-perovskites-synthesis-54tait1vuo.pdf

Recent advances in Re-based double perovskites: Synthesis, structural characterization, physical properties, advanced applications, and theoretical studies

Comparative studies of the structural, magnetic, and optical properties of the sol–gel synthesized Ln0.67Ca0.33MnO3 (Ln = La, Pr, Nd, and Sm) nanoparticles were carried out focusing on the effect of the A-site average cation size ⟨rA⟩. Rietveld refinements of x-ray diffraction data demonstrate all nanoparticles crystallize in an orthorhombic crystal structure (Pnma space group). Their unit cell volumes and the Mn–O–Mn bond angle decreased with reducing ⟨rA⟩, whereas the Mn–O bond length increased. The morphologies of nanoparticles evolved from spherical to irregular shapes, and their single-crystalline nature was confirmed by HRTEM images. Infrared spectra identified the stretching mode of the Mn–O bond near 600 cm−1, and the softening of this phonon mode as reducing ⟨rA⟩ is ascribed to the elongation of the Mn–O bond length. X-ray photoelectron spectroscopy reveals the mixed Mn3+ and Mn4+ cations with a content ratio of Mn3+/Mn4+ = 2:1, divalent Ca cations, and trivalent rare earth Ln cations in all nanoparticles and oxygen element existing as lattice oxygen and chemically absorbed oxygen. The La0.67Ca0.33MnO3 nanoparticles exhibited ferromagnetic behavior, whereas Ln0.67Ca0.33MnO3 (Ln = Pr, Nd, and Sm) nanoparticles displayed antiferromagnetic behavior and strong exchange bias effect. Temperature dependence of dc magnetizations suggests the spin-glass behavior established in the La0.67Ca0.33MnO3 nanoparticles, while magnetic cluster-glass behavior formed in the Ln0.67Ca0.33MnO3 (Ln = Pr, Nd, and Sm) nanoparticles, in which the charge-ordered and antiferromagnetic phases were completely suppressed. Electronic bandgaps of the nanoparticles were about 1.55 eV–1.66 eV, which was ascribed to the electronic charge transfer between two eg bands of the Mn cation with up-spins and down-spins separated by Hund’s coupling energy.

Comparative studies on the structural, magnetic, and optical properties of perovskite Ln0.67Ca0.33MnO3 (Ln = La, Pr, Nd, and Sm) manganite nanoparticles synthesized by sol–gel method

Structural characterization and magnetic properties of single-crystalline (La0.6Pr0.4)0.67Ca0.33MnO3 nanowires

Electron spin resonance studies of (La0.6Ln0.4)0.67Ca0.33MnO3 (Ln = La, Pr, Nd and Sm) nanoparticles at different temperatures

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