Magnetic and Photoluminescent Coupling in SrTi0.87Fe0.13O3-δ/ZnO Vertical Nanocomposite Films.

Self-assembled growth of SrTi0.87Fe0.13O3-δ (STF)/ZnO vertical nanocomposite films by combinatorial pulsed laser deposition is described. The nanocomposite films form vertically aligned columnar epitaxial nanostructures on SrTiO3 substrates, in which the STF shows room-temperature magnetism. The magnetic properties are discussed in terms of strain states, oxygen vacancies, and microstructures. The nanocomposites exhibit magneto-photoluminescent coupling behavior that the near-band-edge emission of ZnO is shifted as a function of magnetic field.

Magnetostatic Interactions in Self-Assembled CoxNi1-xFe2O4/BiFeO3 Multiferroic Nanocomposites.

Self-assembled vertically aligned oxide nanocomposites consisting of magnetic pillars embedded in a ferroelectric matrix have been proposed for logic devices made from arrays of magnetostatically interacting pillars. To control the ratio between the nearest neighbor interaction field and the switching field of the pillars, the pillar composition CoxNi1-xFe2O4 was varied over the range 0 ≤ x ≤ 1, which alters the magnetoelastic and magnetocrystalline anisotropy and the saturation magnetization. Nanocomposites were templated into square arrays of pillars in which the formation of a "checkerboard" ground state after ac-demagnetization indicated dominant magnetostatic interactions. The effect of switching field distribution in disrupting the antiparallel nearest neighbor configuration was analyzed using an Ising model and compared with experimental results.

SrGa(0.7)Co(0.3)O(3-δ) perovskite-cobalt oxide-metal nanocomposite films: magnetic and optical properties.

Two-phase nanocomposite films consisting of metallic Co nanoparticles below 50 nm diameter in a perovskite matrix were grown by pulsed laser deposition onto (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) and silicon substrates from a target of SrGa0.73Co0.27O3. The particles made up about 6% by volume of the film and were present within the film and at the substrate interface. The saturation magnetization of the film was up to 85 emu cm(-3) at 80 nm thickness and the Faraday rotation (FR) tracked the out-of-plane hysteresis loop, reaching 3000 deg cm(-1) at 10 kOe for 1550 nm wavelength. The magneto-optical figure of merit defined as FR divided by optical absorption was 0.04-0.06 deg dB(-1) due to the high optical absorption of the Co particles.

Multiferroic behavior of templated BiFeO3-CoFe2O4 self-assembled nanocomposites.

Self-assembled BiFeO3-CoFe2O4 nanocomposites were templated into ordered structures in which the ferrimagnetic CoFe2O4 pillars form square arrays of periods 60-100 nm in a ferroelectric BiFeO3 matrix. The ferroelectricity, magnetism, conductivity, and magnetoelectric coupling of the ordered nanocomposites were characterized by scanning probe microscopy. The insulating BiFeO3 matrix exhibited ferroelectric domains, whereas the resistive CoFe2O4 pillars exhibited single-domain magnetic contrast with high anisotropy due to the magnetoelasticity of the spinel phase. Magnetoelectric coupling was observed in which an applied voltage led to reversal of the magnetic pillars.

Combinatorial pulsed laser deposition of magnetic and magneto-optical Sr(GaxTiyFe0.34-0.40)O3-δ perovskite films.

Ferromagnetic Sr(GaxTiyFe0.34-0.40)O3-δ (0.1 ≤ x, y ≤ 0.5) films with single-crystal perovskite structure were epitaxially grown on (001) (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates by combinatorial pulsed laser deposition (CPLD) and compared with previous results from films grown from single targets. In CPLD films the Fe was present as both Fe(2+) and Fe(3+). The distribution of Sr, Ga, Ti, and O was homogeneous, but Fe-rich nanowires with diameter of 3 nm were present perpendicular to the film plane. The unit cell was tetragonally distorted with the ratio of out-of-plane to in-plane lattice parameter decreasing from 1.06 to 1.02 as the Ga content increased. The magnetic easy axis of the films changed from out-of-plane when Ti content y > 0.3 to isotropic as the Ga content increased, consistent with a reduction in magnetoelastic anisotropy. The Ga lowered the Faraday rotation and the magnetization but increased the optical transmittance.

Hierarchical templating of a BiFeO3-CoFe2O4 multiferroic nanocomposite by a triblock terpolymer film.

A process route to fabricate templated BiFeO3/CoFe2O4 (BFO/CFO) vertical nanocomposites is presented in which the self-assembly of the BFO/CFO is guided using a self-assembled triblock terpolymer. A linear triblock terpolymer was selected instead of a diblock copolymer in order to produce a square-symmetry template, which had a period of 44 nm. The triblock terpolymer pattern was transferred to a (001) Nb:SrTiO3 substrate to produce pits that formed preferential sites for the nucleation of CFO crystals, in contrast to the BFO, which wetted the flat regions of the substrate. The crystallographic orientation and magnetic properties of the templated BFO/CFO were characterized.

Templated self-assembly of functional oxide nanocomposites.

In perovskite/spinel self-assembled oxide nanocomposites, the substrate surface plays a dominant role in determining the final morphology. Topgraphic features, such as pits and trenches, are written in the substrate using either Focused Ion Beam or wet etching through a block co-polymer mask. These features are effective at templating the self-assembly, resulting in a wide range of attainable nano-assemblies.

Magnetostriction in epitaxial SrTi(1-x)Fe(x)O(3-δ) perovskite films with x = 0.13 and 0.35.

The crystal structure, magnetic anisotropy and magnetoelasticity of epitaxial SrTi(0.87)Fe(0.13)O(3-δ) (STF13) and SrTi(0.65)Fe(0.35)O(3-δ) (STF35) films grown on (001), (011), and (111) oriented SrTiO(3) substrates were investigated. The films grew with compressive in-plane strain and underwent tetragonal, monoclinic, and rhombohedral distortions on the (001), (011), and (111) substrates, respectively. All samples showed room temperature magnetic hysteresis loops with strong out-of-plane anisotropy. The resulting magnetoelastic anisotropy was an order of magnitude greater than the magnetocrystalline and shape anisotropies. Magnetoelastic coefficients of B(1) =- 6.7 × 10(6) and B(2) =- 28 to -26 × 10(6) erg cm(-3) for STF13 and B(1) =- 2.0 × 10(6) and B(2) =- 5.4 to -3.9 × 10(6) erg cm(-3) for STF35 were determined from the magnetic anisotropy and lattice strain, corresponding to magnetostriction constants of λ(100) = 2.09 × 10(-6) and λ(111) = 7.68 × 10(-6) for STF13, and λ(100) = 0.62 × 10(-6) and λ(111) = 1.07 × 10(-6) for STF35.

Combinatorial pulsed laser deposition of Fe, Cr, Mn, and Ni-substituted SrTiO3 films on Si substrates.

Combinatorial pulsed laser deposition (CPLD) using two targets was used to produce a range of transition metal-substituted perovskite-structured Sr(Ti(1-x)M(x))O(3-δ) films on buffered silicon substrates, where M = Fe, Cr, Ni and Mn and x = 0.05-0.5. CPLD produced samples whose composition vs distance fitted a linear combination of the compositions of the two targets. Sr(Ti(1-x)Fe(x))O(3-δ) films produced from a pair of perovskite targets (SrTiO(3) and SrFeO(3) or SrTiO(3) and SrTi0(0.575)Fe(0.425)O(3)) had properties similar to those of films produced from single targets, showing a single phase microstructure, a saturation magnetization of 0.5 µ(B)/Fe, and a strong out-of-plane magnetoelastic anisotropy at room temperature. Films produced from an SrTiO(3) and a metal oxide target consisted of majority perovskite phases with additional metal oxide (or metal in the case of Ni) phases. Films made from SrTiO(3) and Fe(2)O(3) targets retained the high magnetic anisotropy of Sr(Ti(1-x)Fe(x))O(3-δ), but had a much higher saturation magnetization than single-target films, reaching for example an out-of-plane coercivity of >2 kOe and a saturation magnetization of 125 emu/cm(3) at 24%Fe. This was attributed to the presence of maghemite or magnetite exchange-coupled to the Sr(Ti(1-x)Fe(x))O(3-δ). Films of Sr(Ti(1-x)Cr(x))O(3-δ) and Sr(Ti(1-x)Mn(x))O(3-δ) showed no room temperature ferromagnetism, but Sr(Ti(1-x)Ni(x))O(3-δ) did show a high anisotropy and magnetization attributed mainly to the perovskite phase. Combinatorial synthesis is shown to be an efficient process for enabling evaluation of the properties of epitaxial substituted perovskite films as well as multiphase films which have potential for a wide range of electronic, magnetic, optical, and catalytic applications.