Bangmin Zhang

Tailoring the electronic properties of SrRuO3 films in SrRuO3/LaAlO3 superlattices

The electronic properties of SrRuO3/LaAlO3 (SRO/LAO) superlattices with different interlayer thicknesses of SRO layers were studied. As the thickness of SRO layers is reduced, the superlattices exhibit a metal-insulator transition implying transformation into a more localized state from its original bulk metallic state. The strain effect on the metal-insulator transition was also examined. The origin of the metal-insulator transition in ultrathin SRO film is discussed. All the superlattices, even those with SRO layers as thin as 2 unit cells, are ferromagnetic at low temperatures. Moreover, we demonstrate field effect devices based on such multilayer superlattice structures.

Solution-Processed Highly Superparamagnetic and Conductive PEDOT:PSS/Fe3O4 Nanocomposite Films with High Transparency and High Mechanical Flexibility

Multifunctional films can have important applications. Transparent and flexible films with high conductivity and magnetic properties can be used in many areas, such as electromagnetic interference (EMI) shielding, magnetic switching, microwave absorption, and also biotechnology. Herein, novel highly conductive and superparamagnetic thin films with excellent transparency and flexibility have been demonstrated. The films were formed from a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS; Clevios PH1000) aqueous solution added with iron oxide (Fe3O4) nanoparticles that have a size of ∼20 nm by spin-coating. The PEDOT:PSS/Fe3O4 films have a high conductivity of 1080 S/cm through treatment with methylammonium iodide in an organic solvent. The high-conductivity PEDOT:PSS/Fe3O4 films can also have a saturation magnetization of 25.5 emu/g and an EMI shielding effectiveness of more than 40 dB in the 8-12.5 GHz (X band) frequency range. The PEDOT:PSS/Fe3O4 films have additional advantages, like excellent transparency, good mechanical flexibility, low cost, and light weight. In addition, we fabricate flexible PEDOT:PSS/Fe3O4 silk threads with a high magnetism and conductivity.

Effects of strain relaxation in Pr0.67Sr0.33MnO3 films probed by polarization dependent X-ray absorption near edge structure

The Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate was measured, and the effects of strain relaxation on film properties were investigated. The films showed in-plane compressive and out-of-plane tensile strains. Strain relaxation occurred with increasing film thickness, affecting both lattice constant and MnO6 octahedral rotation. In polarization dependent XANES measurements using in-plane (parallel) and out-of-plane (perpendicular) geometries, the different values of absorption resonance energy Er confirmed the film anisotropy. The values of Er along these two directions shifted towards each other with increasing film thickness. Correlating with X-ray diffraction (XRD) results it is suggested that the strain relaxation decreased the local anisotropy and corresponding probability of electronic charge transfer between Mn 3d and O 2p orbitals along the in-plane and out-of-plane directions. The XANES results were used to explain the film-thickness dependent magnetic and transport properties.

Electric-Field Effect on Magnetic Properties of FePt/PZN-PT Heterostructures

FePt films on PZN-PT single-crystal substrate, the ferromagnetic/piezoelectric (FM/PE) heterostructures, were fabricated by magnetron sputtering. The effects of the electric field on the coercivity and magnetization of the FePt at room temperature in FM/PE heterostructures were investigated. The as-grown FePt film showed an in-plane magnetic anisotropy. Upon applying an electric field, the out-of-plane magnetic loops of the heterostructure changed obviously, but the in-plane loops remained unchanged. When the applied E field increased from 0 to 5 kV/cm, the coercivity of out-of-plane increased from 4614 to 4907 Oe. The change of out-of-plane coercivity with different E field is consistent with the strain-electric-field loop of piezoelectric materials. Therefore, the increase of the coercivity can be attributed to that the electric-field-induced strain resulted in increased anisotropy normal to the film plane. The magnetization reversal process of easy direction was mainly due to domain wall motion, which may explain the invariability of the in-plane loops. Based on these results, it was believed that the electric-field-induced piezoelectric strain from the bottom PZN-PT substrate was effectively transferred to the top FePt layer.

Control of magnetic anisotropy by orbital hybridization with charge transfer in (La 0.67 Sr 0.33 MnO 3 ) n /(SrTiO 3 ) n superlattice

The chemical asymmetry at the hetero-structure interface offers an effective opportunity to design desirable electronic structures by controlling charge transfer and orbital hybridization across the interface. However, controlling the hetero-interface remains a daunting task. Here, we report the modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices by manipulating the periodic thickness with n unit cells of SrTiO3 and n unit cells of La0.67Sr0.33MnO3 with a fixed thickness of ~120 unit cells. The easy axis of magnetic anisotropy rotates ~45° towards the out-of-plane direction from n = 10 to n = 2 at reduced temperature TRe = T/TS = 0.87, where TS is the temperature at the onset of magnetization. Transmission electron microscopy reveals an enlarged tetragonal ratio >1 with breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n interface and electronic charge transfer from Mn to Ti 3d orbitals across the interface. Orbital hybridization accompanying the charge transfer results in preferred occupancy of

Note: Application of a pixel-array area detector to simultaneous single crystal x-ray diffraction and x-ray absorption spectroscopy measurements

{3d}_{3z^2-r^2}

Interfacial Coupling-Induced Ferromagnetic Insulator Phase in Manganite Film.

3d3z2-r2 orbitals at the interface and induces a stronger electronic hopping integral and interfacial magnetic anisotropy along the out-of-plane direction, which contributes to the rotation towards the out-of-plane direction of an effective magnetic easy axis for n = 2. We demonstrate that interfacial orbital hybridization with charge transfer in the superlattice of strongly correlated oxides may be a promising approach to tailor electronic and magnetic properties in device applications.Magnetic materials: Stacking layers for an easy rotationA composite material with tuneable magnetic properties which could add novel functionality to electronic devices has been developed by scientists from Singapore and the USA. The interface between two crystalline materials can exhibit properties differing from those of either substance separately. These interface properties can be extended to three dimensions by stacking alternating thin layers of the two materials, creating a so-called superlattice. Bangmin Zhang from the National University of Singapore and co-workers used this concept to alter the magnetic response of a superlattice consisting of lanthanum strontium manganite and strontium titanate. They showed that they could rotate the direction along which the smallest magnetic field is required to magnetize the material by changing the thickness of the layers. This could be useful in devices that are controlled by interaction between electric and magnetic fields.The modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices with n unit cells of SrTiO3 and n unit cells La0.67Sr0.33MnO3, offers an effective opportunity to control charge transfer and orbital hybridization. The easy axis of magnetic anisotropy rotates ~45° towards the out-of-plane direction from n = 10 to n = 2 at reduced temperature TRe = T/TS = 0.87 (TS is onset of magnetization). Orbital hybridization accompanying the charge transfer results in preferred occupancy of