Leyi Zhu

Room-Temperature Multiferroic Hexagonal LuFeO3 Films

The crystal and magnetic structures of single-crystalline hexagonal LuFeO(3) films have been studied using x-ray, electron, and neutron diffraction methods. The polar structure of these films are found to persist up to 1050 K; and the switchability of the polar behavior is observed at room temperature, indicating ferroelectricity. An antiferromagnetic order was shown to occur below 440 K, followed by a spin reorientation resulting in a weak ferromagnetic order below 130 K. This observation of coexisting multiple ferroic orders demonstrates that hexagonal LuFeO(3) films are room-temperature multiferroics.

Structure and magnetotransport properties of epitaxial nanocomposite La0.67Ca0.33MnO3:SrTiO3 thin films grown by a chemical solution approach

Epitaxial La0.67Ca0.33MnO3:SrTiO3 (LCMO:STO) composite thin films have been grown on single crystal LaAlO3(001) substrates by a cost effective polymer-assisted deposition method. Both x-ray diffraction and high-resolution transmission electron microscopy confirm the growth of epitaxial films with an epitaxial relationship between the films and the substrates as (002)film||(002)sub and [202]film||[202]sub. The transport property measurement shows that the STO phase significantly increases the resistivity and enhances the magnetoresistance (MR) effect of LCMO and moves the metal-insulator transition to lower temperatures. For example, the MR values measured at magnetic fields of 0 and 3 T are −44.6% at 255 K for LCMO, −94.2% at 125 K for LCMO:3% STO, and −99.4% at 100 K for LCMO:5% STO, respectively.

Growth Diagram and Magnetic Properties of Hexagonal LuFe2O4 Thin Films

A growth diagram of Lu-Fe-O compounds on an MgO (111) substrate using pulsed laser deposition is constructed according to the experimental data. The LuFe2O4 phase can only be grown in a small range of temperature and O2 pressure conditions. Fundamental understanding of the growth mechanism of Lu-Fe-O compound films are gained in terms of the thermal chemistry at the surface. Superparamagnetism is observed in a film of LuFe2O4 clusters separated by the hexagonal LuFeO3 phase and structural defects.

Crystal field splitting and optical bandgap of hexagonal LuFeO3 films

Hexagonal LuFeO3 films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of Fe3+ is extracted as Ee′−Ee″=0.7 eV and Ea1′−Ee′=0.9 eV, and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow Ea1′>Ee′>Ee″ with slightly underestimated values and a bandgap of 1.35 eV.

Structural and electronic origin of the magnetic structures in hexagonal LuFeO3

Using combined theoretical and experimental approaches, we studied the structural and electronic origin of the magnetic structure in hexagonal LuFeO

Enhancement of vortex pinning in superconductor/ferromagnet bilayers via angled demagnetization

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Structural and magnetic properties in the quantum S = 1 2 dimer system Ba 3 (Cr 1 − x V x ) 2 O 8 with site disorder

. Besides showing the strong exchange coupling that is consistent with the high magnetic ordering temperature, the previously observed spin reorientation transition is explained by the theoretically calculated magnetic phase diagram. The structural origin of this spin reorientation that is responsible for the appearance of spontaneous magnetization, is identified by theory and verified by x-ray diffraction and absorption experiments.

Tuning Vortex Confinement by Magnetic Domains in a Superconductor/Ferromagnet Bilayer

We use local and global magnetometry measurements to study the influence of magnetic domain width

Negative Hall coefficient of ultrathin niobium in Si/Nb/Si trilayers

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Ultrathin Niobium in the Si/Nb/Si Trilayers

on the domain-induced vortex pinning in superconducting/ferromagnetic bilayers, built of a Nb film and a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy, with an insulating layer to eliminate the proximity effect. The quasiperiodic domain patterns with different and systematically adjustable width