I. V. Borisenko

Magnetotransport characteristics of strained La0.7Sr0.3MnO3 epitaxial manganite films

The electrical and magnetic characteristics of La0.7Sr0.3MnO3 (LSMO) epitaxial manganite films are investigated by different methods under conditions when the crystal structure is strongly strained as a result of mismatch between the lattice parameters of the LSMO crystal and the substrate. Substrates with lattice parameters larger and smaller than the nominal lattice parameter of the LSMO crystal are used in experiments. It is shown that the behavior of the temperature dependence of the electrical resistance for the films in the low-temperature range does not depend on the strain of the film and agrees well with the results obtained from the calculations with allowance made for the interaction of electrons with magnetic excitations in the framework of the double-exchange model for systems with strongly correlated electronic states. Investigations of the magneto- optical Kerr effect have revealed that an insignificant (0.3%) orthorhombic distortion of the cubic lattice in the plane of the NdGaO3(110) substrate leads to uniaxial anisotropy of the magnetization of the film, with the easy-magnetization axis lying in the substrate plane. However, LSMO films on substrates (((LaAlO3)0.3+(Sr2AlTaO6)0.7)(001)) ensuring minimum strain of the films exhibit a biaxial anisotropy typical of cubic crystals. The study of the ferromagnetic resonance lines at a frequency of 9.76 GHz confirms the results of magnetooptical investigations and indicates that the ferromagnetic phase in the LSMO films is weakly inhomogeneous.

Magnetotransport characteristics of strained La{sub 0.7}Sr{sub 0.3}MnO{sub 3} epitaxial manganite films

The electrical and magnetic characteristics of La0.7Sr0.3MnO3 (LSMO) epitaxial manganite films are investigated by different methods under conditions when the crystal structure is strongly strained as a result of mismatch between the lattice parameters of the LSMO crystal and the substrate. Substrates with lattice parameters larger and smaller than the nominal lattice parameter of the LSMO crystal are used in experiments. It is shown that the behavior of the temperature dependence of the electrical resistance for the films in the low-temperature range does not depend on the strain of the film and agrees well with the results obtained from the calculations with allowance made for the interaction of electrons with magnetic excitations in the framework of the double-exchange model for systems with strongly correlated electronic states. Investigations of the magneto- optical Kerr effect have revealed that an insignificant (0.3%) orthorhombic distortion of the cubic lattice in the plane of the NdGaO3(110) substrate leads to uniaxial anisotropy of the magnetization of the film, with the easy-magnetization axis lying in the substrate plane. However, LSMO films on substrates (((LaAlO3)0.3+(Sr2AlTaO6)0.7)(001)) ensuring minimum strain of the films exhibit a biaxial anisotropy typical of cubic crystals. The study of the ferromagnetic resonance lines at a frequency of 9.76 GHz confirms the results of magnetooptical investigations and indicates that the ferromagnetic phase in the LSMO films is weakly inhomogeneous.

Magnetic anisotropy in strained manganite films and bicrystal junctions

Transport and magnetic properties of LSMO manganite thin films and bicrystal junctions were investigated. Manganite films were epitaxially grown on STO, LAO, NGO and LSAT substrates and their magnetic anisotropy were determined by two techniques of magnetic resonance spectroscopy. Compare with cubic substrates a small (about 0.3 persentage), the anisotropy of the orthorhombic NGO substrate leads to a uniaxial anisotropy of the magnetic properties of the films in the plane of the substrate. Samples with different tilt of crystallographic basal planes of manganite as well as bicrystal junctions with rotation of the crystallographic axes (RB - junction) and with tilting of basal planes (TB - junction) were investigated. It was found that on vicinal NGO substrates the value of magnetic anisotropy could be varied by changing the substrate inclination angle from 0 to 25 degrees. Measurement of magnetic anisotropy of manganite bicrystal junction demonstrated the presence of two ferromagnetically ordered spin subsystems for both types of bicrystal boundaries RB and TB. The magnitude of the magnetoresistance for TB - junctions increased with decreasing temperature and with the misorientation angle even misorientation of easy axes in the parts of junction does not change. Analysis of the voltage dependencies of bicrystal junction conductivity show that the low value of the magnetoresistance for the LSMO bicrystal junctions can be caused by two scattering mechanisms with the spin- flip of spin - polarized carriers due to the strong electron - electron interactions in a disordered layer at the bicrystal boundary at low temperatures and the spin-flip by anti ferromagnetic magnons at high temperatures.

Magnetic anisotropy of strained epitaxial manganite films

The in-plane magnetic anisotropy of epitaxial La0.7Sr0.3MnO3 (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO3 (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0–25.7° to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110)NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110)NGO, (001)SrTiO3, and (001)[(LaAlO3)0.3 + (Sr2AlTaO6)0.7] substrates are compared.

Metal-insulator transition in epitaxial films of LaMnO3 manganites grown by magnetron sputtering

We have studied thin films of LaMnO3 manganite grown by RF magnetron sputtering at high pressure on crystalline substrates with cubic symmetry. It is established that these films exhibit a metal-insulator transition, whereas LaMnO3 grown on orthorhombic substrates remains in a dielectric state. The parameters of the metal-insulator transition have been studied as dependent on the level and symmetry of mechanical stresses that arise during the epitaxial growth of LaMnO3 films on various substrates. The resistance of LaMnO3 films grown on SrTiO3 substrates has been studied as a function of the film thickness. It is found that the presence of excess oxygen due to substitution in the cation system can significantly influence the Mn4+/Mn3+ ion ratio in the film and thus lead to the appearance of the metal-insulator transition.

Characterization and dynamics of [100]-tilted Y-B-C-O bicrystal junctions on Nd-Ga-O/sub 3/

We report on the fabrication technique and electrical properties of Basal Plane Tilted YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting bicrystal Josephson Junctions (BTJ). In order to form the grain boundary in BTJ we apply an inclination of the [001] YBCO basal planes around the direction of {100} YBCO in contrast to the common In-Plane Tilted bicrystal Josephson Junctions (ITJ) where misorientation of the crystallographic axes in the ab-plane of YBCO has been used. Symmetric and asymmetric junctions were fabricated on bicrystal NdGaO/sub 3/ substrates 13-28/spl deg/ tilted from [110] NdGaO/sub 3/. DC and RF properties of the BTJ were investigates at temperatures 4.2-77 K, in magnetic fields up to 100 G, and under influence of electromagnetic radiation of 56 GHz frequency. The experimental dependences of critical current and Shapiro steps from RF current fit the Resistive Shunted model of Josephson junctions (RSJ-model). At T=77 K the BTJ reveal critical current density j/sub C/=0.2-0.5 MA/cm/sup 2/ and characteristic voltage V/sub C/=I/sub C/R/sub N/=0.6-0.9 mV, that makes the junctions promising candidate for practical electronic devices.

Proximity effect and electron transport in oxide hybrid heterostructures with superconducting/magnetic interfaces

We report on electron transport in oxide heterostructures with superconducting/magnetic (S/M) thin film interfaces. The investigated hybrid mesa-heterostructures consist of a cuprate superconductor, a nonsuperconducting cuprate (antiferromagnetic) or manganite (ferromagnetic) interlayer with thickness d(M) = 5-50 nm and a conventional superconductor (Nb). The superconducting critical current (I-C) with a critical current density j(c) = 10(3) A cm(-2) (for d(M) = 10 nm) and a characteristic voltage ICRN = 100-200 mu V (RN is normal resistance) are observed at liquid helium temperature for a CaXSr1-XCuO2 antiferromagnetic cuprate interlayer with a thickness of d(M) = 10-50 nm. The superconducting current-phase relation of heterostructures deviates from the regular sine type, demonstrating a second harmonic component. These hybrid heterostructures with S/M interfaces show unusually high sensitivity to external magnetic fields. When substituting the cuprate interlayer by a manganite film, no critical current was observed although the manganite interlayer was made several times thinner (down to d(M) <= 5 nm).

Phase dependence of the superconducting current in YBCO Josephson junctions on a bicrystal substrate

AbstractDependences of the amplitudes of the harmonic and subharmonic Shapiro steps on an external monochromatic signal were used to study the current-phase dependence of high-temperature superconducting junctions on a bicrystal substrate. It is shown that for a symmetric definition of the transport current across the junction with an edge transparency of the order of

Magnetoresistance and electrical conductivity of manganite bicrystal contacts

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