V. I. Chichkov

Magnetization and magnetic circular dichroism of La0.7Sr0.3MnO3/YSZ polycrystalline films

The magnetic and magneto-optical properties as well as the surface morphology and structure of La0.7Sr0.3MnO3 polycrystalline films of different thicknesses have been investigated. It has been shown that films have a rough surface with a characteristic in-plane linear dimension of ∼30 nm, and crystallites with linear dimensions of 10–20 nm are randomly oriented in the plane. The temperature and field dependences of the magnetization of the films indicate their magnetic inhomogeneity. The magnetic circular dichroism spectra contain a number of bands, one of which at 2.4 eV is explained by the contribution of conduction electrons.

Linear and quadratic magneto-optical effects observed in La0.7Sr0.3MnO3 thin films in transmitted light

Magnetic linear dichroism (MLD) is observed in polycrystalline La0.7Sr0.3MnO3 films in transmitted light. The spectral and temperature dependences of the MLD are determined for the energy E of the light wave ranging from 1.5 to 3.5 eV. The experimental spectra are fitted by a sum of Lorentzian curves. The MLD spectrum exhibits more features in comparison to the spectra of magnetic circular dichroism (MCD), which we measured earlier using the same film samples. Various temperature behaviors of the intensities of the Lorentzian components centered at different E values have been revealed. This can be related to the effect of the surface states on the magneto-optical characteristics of the samples.

Electron paramagnetic resonance studies of GdMnO3 single crystal and thin film deposited onto a LaAlO3 substrate

Electronic paramagnetic resonance (EPR) spectra of a GdMnO3 single crystal and GdMnO3/LaAlO3 thin film have been measured at X- and Q-band frequencies in the temperature range from 4.2 to 300 K. It is found that the EPR spectrum of a GdMnO3 single crystal consists of only one broad exchange-narrowed line. Unusual magnetism is observed at the interface between the GdMnO3 thin film and LaAlO3 substrate, where it is possible to see the fine structure of the EPR spectrum for a Gd3+ ion. The parameters characterizing the fine structure related to the Gd3+ ion in the GdMnO3 film deposited onto the LaAlO3 substrate are determined.

Magnetic and optical properties of multiferroic GdMnO3 film

We report on magneto-optical studies of an epitaxial thin film of GdMnO3 grown on SrTiO3. Significant differences were found between the magneto-optical and absorption spectra, which highlight the importance of magneto-optics in determining the magnetic character of the optical transitions. Two main features were identified in the magnetic circular dichroism (MCD) spectra: the charge transfer transition between Mn d states at ~2eV and the band edge transition from the oxygen p band to the d states at ~3eV. The strength of the MCD at ~2eV correlates well with the Mn spin ordering, indicating the applicability of magneto-optics for understanding the magnetic properties.

Determination of the Current–Phase Relation in Josephson Junctions by Means of an Asymmetric Two-Junction SQUID

An analytical approach that makes it possible to reconstruct the current–phase relation (CPR) in Josephson structures included in one of the arms of a two-junction superconducting quantum interference device (SQUID), where the second junction has a significantly higher critical current and a known (sinusoidal) CPR, has been developed. The developed methods of analytical and numerical studies of current–flow transformations in two-junction SQUIDs make it possible to reconstruct the CPR of a junction with a low critical current taking into account both the existence of the self-inductance of the interferometer contour and a possible asymmetry in the supply current system. The efficiency of this approach has been confirmed by the experimental study of niobium–aluminum/aluminum oxide–niobium test structures with the known CPR.

EPR spectra of a GdMnO3 thin film on a SrTiO3 substrate

Electron paramagnetic resonance (EPR) spectra of a GdMnO3/SrTiO3 thin film in the X band have been measured in the temperature interval from 200 to 450 K. Signals from two types of paramagnetic centers have been observed in the spectra. The first paramagnetic center is a subsystem of Gd3+ ions, in the EPR spectrum of which the fine structure lines are resolved below 350 K. The second paramagnetic center is a system of manganese and gadolinium ions, in the EPR spectrum of which an exchange-narrowed line is observed with the width ΔH several times less than the width ΔH of an exchange-narrowed line observed in the GdMnO3 single crystal. Unusual magnetic properties are due to the mismatch of the lattice parameters of the GdMnO3 thin film and the SrTiO3 substrate.

The growth, structure, and magnetic properties of thin epitaxial films of GdMnO3 multiferroics

Thin epitaxial gadolinium manganite (GdMnO3) films were manufactured on single-crystal substrates of neodymium gallate (001) (NdGaO3) and strontium titanate (001) (SrTiO3) by the high-frequency magnetron sputtering method. The RBS analysis demonstrated that the thickness of the obtained films was ∼100 nm and the chemical composition corresponded to the stated stoichiometry. It was established by the X-ray diffraction analysis of the structure and phase composition of the obtained films that all films were single-phase but, depending on the temperature of the substrate during sputtering they have one or several types of orientations relative to the substrate. The X-ray diffraction analysis and high-resolution electron microscopy data on gadolinium manganite films on neodymium gallate substrates were verified. Features pointing to phase transitions in GdMnO3 that were earlier discovered on bulk single-crystal samples were found in the temperature dependence of the magnetic susceptibility.

Oscillation of the multiferroic/ferroelectric GdMnO3/SrTiO3 and YbMnO3/SrTiO3 interfaces in the EPR spectrum

The electron paramagnetic resonance (EPR) method was used to study thin manganite ytterbium YbMnO3 and gadolinium GdMnO3 films, with a thickness of 100 nm, deposited on a SrTiO3 virtual ferroelectric backing (GdMnO3/SrTiO3 and YbMnO3/SrTiO3). The most interesting results are obtained in the 40–100 K temperature interval for GdMnO3/SrTiO3, and 40–150 K for YbMnO3/SrTiO3. In these temperature ranges, in addition to the exchange-narrowed line from all film material, absorbed power oscillations were observed in the EPR spectra, with the amplitude of the oscillations depending on both the temperature and the magnitude of the external magnetic field.

Magnetic and magnetooptical properties of polycrystalline films of La0.7Sr0.3MnO3

Magnetic circular dichroism (MCD) is studied in comparison with the magnetic behavior of polycrystalline films of La0.7Sr0.3MnO3 (LSMO) deposited on a single crystal of zirconium oxide stabilized by yttrium (YSZ). It is found that the bands observed in MCD spectra are characterized by different temperature dependences.

Temperature features of the EPR spectrum of GdMnO3: Single crystal and thin film GdMnO3/LaAlO3

Electron paramagnetic resonance (EPR) spectra of GdMnO3 single crystal and GdMnO3/LaAlO3 thin film are measured at Q-band frequency in the temperature range of 4.2 to 300 K. The temperature dependence of parameters of the spin Hamiltonian corresponding to the monoclinic symmetry of such paramagnetic centers as Gd3+ ions in the GdMnO3/LaAlO3 film is determined.