X.P. Wang

Magnetic and charge ordering in nanosized manganites

Perovskite manganites exhibit a wide range of functional properties, such as colossal magneto-resistance, magnetocaloric effect, multiferroic property, and some interesting physical phenomena including spin, charge, and orbital ordering. Recent advances in science and technology associated with perovskite oxides have resulted in the feature sizes of microelectronic devices down-scaling into nanoscale dimensions. The nanoscale perovskite manganites display novel magnetic and electronic properties that are different from their bulk and film counterparts. Understanding the size effects of perovskite manganites at the nanoscale is of importance not only for the fundamental scientific research but also for developing next generation of electronic and magnetic nanodevices. In this paper, the current understanding and the fundamental issues related to the size effects on the magnetic properties and charge ordering in manganites are reviewed, which covers lattice structure, magnetic and electronic properties in both ferromagnetic and antiferromagnetic based manganites. In addition to review the literatures, this article identifies the promising avenues for the future research in this area.

Manufacture, microstructure and mechanical properties of Mo-W-N nanostructured hard films

Mo1−xWxNy (x = 0–0.67) hard films were fabricated on wafers of silicon and high speed steel by dc magnetron sputtering technique. The effect of tungsten concentration on the phase composition, microstructure, surface morphology, hardness, adhesion, and corrosion resistance of the films was studied by X-ray diffraction, scanning electron microscopy, nano-indentation, and scratch test. It was found that if the W concentration (x) in the film is in the range of 0–0.52, the films exhibit fcc (Mo,W)Ny single phase where larger W atoms substituted Mo atoms in fcc MoNy. At higher x values (x > 0.52) the films exhibit a two-phase structure consisting of fcc (Mo,W)Ny and pure bcc tungsten phase. The hardness of the Mo1−xWxNy films increases at first with increasing x, and then decreases after passing a maximum. The maximum hardness of 47 GPa is obtained at x = 0.37 corresponding to an adhesion strength of 60 N. The Mo–W–N coated high speed steel has a lower corrosion current density and higher corrosion potential than the bare high speed steel substrates.

Optical spectroscopy and energy transfer of Er3+/Ce3+ in B2O3-doped bismuth-silicate glasses

Ce3+ and B2O3 are introduced into erbium-doped Bi2O3-SiO2 glass to enhance the luminescence emission and optic spectra characters of Er3+. The energy transfer from Er3+ to Ce3+ will obviously be improved with the phonon energy increasing by the addition of B2O3. Here, the nonradiative rate, the lifetime of the 4I11/2→4I13/2 transition, and the emission intensity and bandwidth of the 1.5 μm luminescence with the 4I13/2→4I15/2 transition of Er3+ are discussed in detail. The results show that the optical parameters of Er3+ in this bismuth-borate-silicate glass are nearly as good as that in tellurite glass, and the physical properties are similar to those in silicate glass. With the Judd-Ofelt and nonradiative theory analyses, the multiphonon decay and phonon-assisted energy-transfer (PAT) rates are calculated for the Er3+/Ce3+ codoped glasses. For the PAT process, an optimum value of the glass phonon energy is obtained after B2O3 is introduced into the Er3+/Ce3+ codoped bismuth-silicate glasses, and it much improves the energy-transfer rate between Er3+4I11/2→4I13/2 and Ce3+2F5/2→2F7/2, although there is an energy mismatch.

Nanometer size effect on the structure and magnetic properties of high oxygen content ferromagnetic PrMnO3+δ nanoparticles

Structure and magnetic properties of undoped PrMnO3+δ nanoparticles with average particle size ranging from 40–500 nm have been investigated. Compared with bulk PrMnO3 compound with A type antiferromagnetic ordering below TN=95 K, PrMnO3+δ nanoparticles exhibit ferromagnetic ordering. With decreasing particle size, the MnO6 octahedra distortion increases, the cell volume shrinks, the average Mn–O bond length increases and the Mn–O–Mn bond angle decreases; the ferromagnetism becomes weak and the Curie temperature decreases gradually, and meanwhile, the spin glass behavior becomes more obvious. However, in contrast to antiferromagnetic nanoparticles, no exchange bias phenomenon was observed in our case. These interesting results are attributed to the excessive oxygen content and surface effects.

Internal friction study of oxygen ion conductors La1.95K0.05Mo2−xTxO9−δ (T=Fe,Mn)

Based on the oxygen ion conductor La 2 Mo 2 O 9 , a series of K, Fe, and Mn doped samples La 1.95 K 0.05 Mo 2 − x T x O 9 − δ ( T = Fe , Mn ; x = 0 , 0.025 , 0.05 , 0.1 ) were prepared with conventional solid-state reaction method. The effects of Fe and Mn doping on the cationic and anionic ionsdiffusion,phase transition, and electrical conductivity were studied. The mechanical spectroscopy (or internal friction) technique was exploited to investigate the microscopic transport mechanism and to deduce the dynamical relaxation parameters. Three internal friction peaks ( P L , P H , and P M ) were observed in the La 1.95 K 0.05 Mo 2 − x T x O 9 − δ samples, among which P L and P M are of relaxational type while P H is associated with a kind of phase transition. The results revealed that peak P L is originated from the short-distance jumps of oxygen vacancies, while peak P M is associated with the short-distance diffusion of Mn (Fe) ions and peak P H with the phase transition from the static disordered state to the dynamic disordered state of oxygen ion distribution. Based on the results of conductivity measurements, it can be concluded that the high-temperature conductivity of La 2 Mo 2 O 9 can be improved obviously by the Fe or Mn doping at Mo site and the low-temperature conductivity can be increased by the simultaneous K doping at La site.

In situ control of electronic phase separation in La1/8 Pr4/8Ca3/8MnO3/PNM-PT thin films using ferroelectric-poling-induced strain

The effects of ferroelectric-poling-induced strain on the transport and magnetic properties of the phase separated La1/8Pr4/8Ca3/8MnO3 (LPCMO) thin films epitaxially grown on the ferroelectric 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-PT) single-crystal substrates were investigated. The ferroelectric poling reduces the in-plane tensile strain and enhances the out-of plane tensile strain of LPCMO film, which decreases the resistance and the charge ordering transition temperature but raises the low-field-magnetization of film. These results can be explained by the strain induced change in the volume fraction of coexisting phases, i.e., ferromagnetic, antiferromagnetic, and paramagnetic phases, demonstrating that the charge ordering phase transition of manganites film grown on the ferroelectric PMN-PT substrate can be controlled by modifying the poling state of single crystal substrate.