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Register a new userManipulation of the magnetic order parameter and the metal-insulator-transition of a manganite thin film with applied elastic stress
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We measured the temperature dependence of the saturation magnetization (Ms) of a (La1-xPrx)1-yCayMnO3 (x ~ 0.60, y ~ 0.33) film as a function of applied bending stress. Stress producing a compressive strain of -0.01% along the magnetic easy axis increased the Curie temperature by ~6 K and the metal-insulator-transition by ~4 K. Regardless of whether or not stress is applied to the film, magnetic ordering occurs at temperatures significantly higher than the metal-insulator-transition temperature. The magnetization of the sample at the temperature of the metal-insulator-transition is approximately the site percolation threshold for a two-dimensional spin lattice.
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We measured the magnetization depth profile of a (La1-xPrx)1-yCayMnO3 (x = 0.60pm0.04, y = 0.20pm0.03) film as a function of applied bending stress using polarized neutron reflectometry. From these measurements we obtained a coupling coefficient relating strain to the depth dependent magnetization. We found application of compressive (tensile) bending stress along the magnetic easy axis increases (decreases) the magnetization of the film.
We performed resonant and nonresonant x-ray diffraction studies of a Nd0.5Sr0.5MnO3 thin film that exhibits a clear first-order transition. Lattice parameters vary drastically at the metal-insulator transition at 170K (=T_MI), and superlattice reflections appear below 140K (=T_CO). The electronic structure between T_MI and T_CO is identified as A-type antiferromagnetic with the d_{x2-y2} ferroorbital ordering. Below T_CO, a new type of antiferroorbital ordering emerges. The accommodation of the large lattice distortion at the first-order phase transition and the appearance of the novel orbital ordering are brought about by the anisotropy in the substrate, a new parameter for the phase control.
Cd2Os2O7 shows a peculiar metal-insulator transition at 227 K with magnetic ordering in a frustrated pyrochlore lattice, but its magnetic structure in the ordered state and the transition origin are yet uncovered. We observed a commensurate magnetic peak by resonant x-ray scattering in a high-quality single crystal. X-ray diffraction and Raman scattering experiments confirmed that the transition is not accompanied with any spatial symmetry breaking. We propose a noncollinear all-in/all-out spin arrangement on the tetrahedral network made of Os atoms. Based on this we suggest that the transition is not caused by Slater mechanism as believed earlier but by an alternative mechanism related to the formation of the specific tetrahedral magnetic order on the pyrochlore lattice in the presence of strong spin-orbit interactions.
We have analyzed spectral weight changes in the conduction and the valence band across insulator to metal transition (IMT) in the VO2 thin film using X-ray absorption spectroscopy (XAS) and resonant photoemission spectroscopy (PES). Through temperature dependent XAS and resonant PES measurements we unveil that spectral changes in the d$_{|}$ states (V 3$it{d_{x^2-y^2}}$ orbitals) are directly associated with temperature dependent electrical conductivity. Due to presence of the strong electron-electron correlations among the d$_{|}$ states, across IMT, these states are found to exhibit significant intensity variation compared to insignificant changes in the $pi^{ast}$ and the $sigma^{ast}$ states (which are O 2$it{p}$ hybridized V 3$it{d}$ $e_g^{pi}$ and $e_g^{sigma}$ states) in the conduction band. Experimentally obtained values of the correlation parameter (U$_{dd}$ $sim$ 5.1 eV, intra-atomic V 3$it{d}$ correlations) and crystal field splitting (10 Dq $sim$ 2.5 eV) values are used to simulate the V $it{L_{2,3}}$ edge XAS spectra and an agreement between simulated and experimental spectra also manifests strong correlations. These results unravel that the IMT observed in the VO2 thin film is the Mott-Hubbard insulator-metal transition.
The control of materials properties with light is a promising approach towards the realization of faster and smaller electronic devices. With phases that can be controlled via strain, pressure, chemical composition or dimensionality, nickelates are good candidates for the development of a new generation of high performance and low consumption devices. Here we analyze the photoinduced dynamics in a single crystalline NdNiO$_3$ film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally we compare our results to similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced phase transitions.
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