Magnetization reversal in as-grown and annealed NiFe2O4 / SrTiO3(0 0 1) epitaxial heterostructures, prepared by laser molecular beam epitaxy (LMBE), was studied using magneto-optical technique in geometry of polar (PMOKE) and longitidual (LMOKE) Kerr effect. It was found that the hysteresis loops of polarization plane rotation and ellipticity measured in LMOKE geometry are combinations of symmetric (even in magnetic field) SPart and antisymmetric (odd in magnetic field) AsPart parts, caused by quadratic (QMOKE ∼ MiMj) and linear (LMOKE ∼ Mi) in magnetization M contributions, correspondingly. The angular dependences of SPart demonstrate in-plane biaxial magnetic anisotropy (BMA) and show that magnetization reversal in as-grown structures occurs by one jump (1j) process, in contrast to the annealed structures, in which two jumps (2j) process takes place when the deviation of magnetic field from the hard axis is less than ∼20°. Analysis within the framework of the Stoner-Wohlfarth (SW) model with account of domain mechanism of magnetization jumps shows that the first jump occurs due to formation and movement of domain walls. Second jump is remarkably diffused, that is associated with the dispersion of the biaxial anisotropy field Ha and misorientations of the magnetic easy axes in different regions of the film. Narrow and strong FMR lines are observed in the most perfect structures in which the diffusion of the second jump is small. The degree of second jump diffusion can be used to assess the structural perfection of the films.

Magnetization reversal in as-grown and annealed NiFe2O4 / SrTiO3(001) epitaxial heterostructures, prepared by laser molecular beam epitaxy (LMBE), was studied using magneto-optical technique in geometry of polar (PMOKE) and longitidual (LMOKE) Kerr effect. It was found that the hysteresis loops of polarization plane rotation and ellipticity measured in LMOKE geometry are combinations of symmetric (even in magnetic field) SPart and antisymmetric (odd in magnetic field) AsPart parts, caused by quadratic (QMOKE similar to MiMj) and linear (LMOKE similar to M-i) in magnetization M contributions, correspondingly. The angular dependences of SPart demonstrate in-plane biaxial magnetic anisotropy (BMA) and show that magnetization reversal in as-grown structures occurs by one jump (1(j)) process, in contrast to the annealed structures, in which two jumps (2(j)) process takes place when the deviation of magnetic field from the hard axis is less than similar to 20 degrees. Analysis within the framework of the Stoner-Wohlfarth (SW) model with account of domain mechanism of magnetization jumps shows that the first jump occurs due to formation and movement of domain walls. Second jump is remarkably diffused, that is associated with the dispersion of the biaxial anisotropy field H-a and misorientations of the magnetic easy axes in different regions of the film. Narrow and strong FMR lines are observed in the most perfect structures in which the diffusion of the second jump is small. The degree of second jump diffusion can be used to assess the structural perfection of the films.

Nanosized Y3Fe5O12 epitaxial films have been grown on Nd3Ga5O12 substrates using laser molecular beam epitaxy method. Magneto-optical polar Kerr effect, ferromagnetic resonance and spin wave propagation measurements show that the stress-related anisotropy field has an opposite sign, compared to that in the YIG/GGG systems. This leads to a considerable decrease of the effective magnetization that opens a perspective to get YIG films with perpendicular magnetization for utilizing forward volume spin waves. Longitudinal magnetooptical Kerr effect magnetometry reveals a large contribution of quadratic in magnetization terms into dielectric permittivity tensor at optical frequencies. This effect strongly increases with temperature decrease and is explained by magnetization of the interface Nd3+ ions that are exchange coupled to the Fe3+ ions.

Nickel ferrite (NiFe2O4, NFO) films were grown at high temperatures on SrTiO3(001) substrates using laser molecular beam epitaxy. A spinel lattice structure, with lattice parameters close to those of bulk NFO, was confirmed by electron and X-ray diffraction. Vibrating sample magnetometer measurements show an in-plane remanent magnetization, relatively narrow (similar to 50 Oe) hysteresis loops, and fourfold symmetry. Soft X-ray magnetic dichroism measurements indicate an inverse spinel structure. X-band ferromagnetic resonance (FMR) measurements show a line width as low as 45-50 Oe, which corresponds to the value for bulk NFO crystals. The angular dependence of FMR on a 110 nm thick NFO film indicates cubic anisotropy close to that of bulk crystals and a substrate-induced stress anisotropy field of about 0.4 kG.

Epitaxial layers of CoFeB were grown on MgO by means of laser molecular beam epitaxy using Co40Fe40B20 target. The growth was combined with in situ structural characterization by three-dimensional reciprocal space mapping obtained from reflection high energy electron diffraction (RHEED) data. High-temperature single stage growth regime was adopted to fabricate CoFeB layers. As confirmed by the atomic force microscopy, the surface of CoFeB layers consists of closely spaced nanometer sized islands with dimensions dependent on the growth temperature. As shown by RHEED and XRD analysis, the CoFeB layers grown at high-temperature on MgO(001) possess body centered cubic (bcc) crystal structure with the lattice constant a = 2.87 angstrom close to that of the Co75Fe25 alloy. It was further shown that following the same high-temperature growth technique the MgO/CoFeB/MgO(001) heterostructures can be fabricated with top and bottom MgO layers of the same crystallographic orientation. The CoFeB layers were also grown on the GaN(0001) substrates using MgO(111) as a buffer layer. In this case, the CoFeB layers crystallize in bcc crystal structure with the (111) axis perpendicular to the substrate surface. The magnetic properties of the CoFeB/MgO (001) heterostructures have been investigated by measuring magnetization curves with a vibrating sample magnetometer as well as by performing magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR) studies. FMR spectra were obtained for the variety of the magnetic field directions and typically consisted of a single relatively narrow resonance line. The magnetization orientations and the resonance conditions were calculated in the framework of a standard magnetic energy minimization procedure involving a single K-1c cubic term for the magnetocrystalline anisotropy. This allows a fairly accurate description of the angular dependences of the resonance fields-both in-plane and out-of-plane. It was shown that CoFeB layers exhibit in-plane fourth-order magnetic anisotropy. A two-step magnetization reversal model has been adopted for the CoFeB layers based on the VSM measurement analysis. Magnetization reversal studies performed by polar MOKE indicate that the magnetization lies in-plane in absence of magnetic field. Observed magnetic field dependences of reflected light ellipticity in geometry of longitudinal Kerr effect give convincing evidence for contribution of quadratic in magnetization terms in the dielectric tensor and clearly show the in-plane magnetization rotation.

Relaxation losses of magnetic excitations in nanoscale films of Y3Fe5O12 (YIG) were studied. The films were obtained by laser molecular-beam epitaxy (LMBE). Ferromagnetic resonance linewidth ΔH was found to increase sharply as the temperature decreased from 300 to 77 K. The observed growth of ΔH is explained by typical relaxation processes caused by the presence of Fe2+ ions. This effect is not observed in thick films of YIG grown by liquid-phase epitaxy and containing Pb4+ ions, and, hence, we have concluded that the presence of acceptor ions in YIG films obtained by LMBE will facilitate decreasing the concentration of Fe2+ ions and, a result, diminishing relaxation losses.

S. M. Suturin,1,* A. M. Korovin,1 V. E. Bursian,1 L. V. Lutsev,1 V. Bourobina,1 N. L. Yakovlev,2 M. Montecchi,3 L. Pasquali,3,4,5 V. Ukleev,6 A. Vorobiev,7 A. Devishvili,8 and N. S. Sokolov1 1Ioffe Institute, 26 Polytechnicheskaya Street, St. Petersburg 194021, Russia 2Institute of Materials Research and Engineering, Agency for Science Technology and Research (A*STAR), 138634 Singapore 3Engineering Department, “E. Ferrari” University of Modena e Reggio Emilia, Via Vigolese 905, 41125 Modena, Italy 4IOM-CNR Institute, Area Science Park, Strada Statale 14, km 163.5, 34149 Basovizza, Trieste, Italy 5Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006, South Africa 6Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), CH-5232, Villigen, Switzerland 7Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120, Uppsala, Sweden 8Department of Physical Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden

We have clarified the origin of a magnetically dead interface layer formed in yttrium iron garnet (YIG) films grown at above 700 degrees C onto a gadolinium gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The diffusion-assisted formation of a Ga-rich region at the YIG/GGG interface is demonstrated by means of composition depth profiling performed by x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and x-ray and neutron reflectometry. Our finding is in sharp contrast to the earlier expressed assumption that Gd acts as a migrant element in the YIG/GGG system. We further correlate the presence of a Ga-rich transition layer with considerable quenching of ferromagnetic resonance and spin wave propagation in thin YIG films. Finally, we clarify the origin of the enigmatic low-density overlayer that is often observed in neutron and x-ray reflectometry studies of the YIG/GGG epitaxial system.

AbstractRelaxation losses of magnetic excitations in nanoscale films of Y_3Fe_5O_12 (YIG) were studied. The films were obtained by laser molecular-beam epitaxy (LMBE). Ferromagnetic resonance linewidth Δ H was found to increase sharply as the temperature decreased from 300 to 77 K. The observed growth of Δ H is explained by typical relaxation processes caused by the presence of Fe^2+ ions. This effect is not observed in thick films of YIG grown by liquid-phase epitaxy and containing Pb^4+ ions, and, hence, we have concluded that the presence of acceptor ions in YIG films obtained by LMBE will facilitate decreasing the concentration of Fe^2+ ions and, a result, diminishing relaxation losses.

We describe synthesis of submicron Y3Fe5O12 (YIG) films sputtered on GaAs-based substrates and present results of the study of ferromagnetic resonance (FMR), spin wave propagation and interaction between spin excitations and 2D electrons in interface layer in YIG/AlOx/ GaAs-heterostructures. It is found that the contribution of the relaxation process to the FMR linewidth is about 3.6%-6.6% of the linewidth Delta H. Thhe main contribution to the FMR linewidth of sputtered YIG films is given by a magnetic profile inhomogeneity. Transistor structures with two-dimensional electron gas (2EFG) channels in AlOx/GaAs interface governed by YIG-film spin excitations are designed. An effective influence of spin excitations on the current flowing through the GaAs 2DFG channel is observed. It is found that the light illumination results in essential changes in the YIGfilmm FMR spectrum of transistor structures-an increase of the 2EFG current induced by light leads to an inverse effect, which represents essential changes in the FMR spectrum.

Abstract Thin (4–20 nm) yttrium iron garnet (Y3Fe5O12, YIG) layers have been grown on gadolinium gallium garnet (Gd3Ga5O12, GGG) 111-oriented substrates by laser molecular beam epitaxy in 700–1000 °C growth temperature range. The layers were found to have atomically flat step-and-terrace surface morphology with step height of 1.8 Å characteristic for YIG(111) surface. As the growth temperature is increased from 700 to 1000 °C the terraces become wider and the growth gradually changes from layer by layer to step-flow regime. Crystal structure studied by electron and X-ray diffraction showed that YIG lattice is co-oriented and laterally pseudomorphic to GGG with small rhombohedral distortion present perpendicular to the surface. Measurements of magnetic moment, magneto-optical polar and longitudinal Kerr effect (MOKE), and X-ray magnetic circular dichroism (XMCD) were used for study of magnetization reversal for different orientations of magnetic field. These methods and ferromagnetic resonance studies have shown that in zero magnetic field magnetization lies in the film plane due to both shape and induced anisotropies. Vectorial MOKE studies have revealed the presence of an in-plane easy magnetization axis. In-plane magnetization reversal was shown to occur through combination of reversible rotation and abrupt irreversible magnetization jump, the latter caused by domain wall nucleation and propagation. The field at which the flip takes place depends on the angle between the applied magnetic field and the easy magnetization axis and can be described by the modified Stoner–Wohlfarth model taking into account magnetic field dependence of the domain wall energy. Magnetization curves of individual tetrahedral and octahedral magnetic Fe3+ sublattices were studied by XMCD.

Synthesis of nanosized yttrium iron garnet (Y3Fe5O12, YIG) films followed by the study of ferromagnetic resonance (FMR) and spin wave propagation in these films is reported. The YIG films were grown on gadolinium gallium garnet substrates by laser molecular beam epitaxy. It has been shown that spin waves propagating in YIG deposited at 700 °C have low damping. At the frequency of 3.29 GHz, the spin-wave damping parameter is less than 3.6 × 10−5. Magnetic inhomogeneities of the YIG films give the main contribution to the FMR linewidth. The contribution of the relaxation processes to the FMR linewidth is as low as 1.2%.

Yttrium iron garnet (YIG) films were grown on GaN substrates using the laser molecular beam epitaxy method. X-ray diffraction data showed polycrystalline YIG layers without additional structural modifications. The magnetic properties of the YIG films were studied at room temperature with the aid of a vibration sample magnetometer, the magneto-optical Kerr effect and ferromagnetic resonance methods. 'Easy-plane'-type magnetic anisotropy was found in the films. The gyromagnetic ratio and 4 pi M-S value were calculated.

Laser molecular-beam epitaxy has been employed to obtain layers of yttrium-iron garnet (YIG) Y3Fe5O12 on gallium nitride substrates. It was found that there exists a polycrystalline YIG phase without admixtures of other structural phases. A magnetic anisotropy of films of the “easy-magnetic plane” type was found. The gyromagnetic ratio and the demagnetizing field 4πM S were calculated.

Методом лазерной молекулярно-лучевой эпитаксии получены слои железоиттриевого граната (ЖИГ) Y3Fe5O12 на подложках нитрида галлия. Выявлено наличие поликристаллической фазы ЖИГ без примесей иных структурных фаз. Была выявлена магнитная анизотропия пленок типа "легкая плоскость". Были вычислены гиромагнитное отношение и значение поля рассеяния 4pi MS.

Pulsed laser deposition has been used to grow thin (10–84 nm) epitaxial layers of Yttrium Iron Garnet Y3Fe5O12 (YIG) on (111)–oriented Gadolinium Gallium Garnet substrates at different growth conditions. Atomic force microscopy showed flat surface morphology both on micrometer and nanometer scales. X-ray diffraction measurements revealed that the films are coherent with the substrate in the interface plane. The interplane distance in the [111] direction was found to be by 1.2% larger than expected for YIG stoichiometric pseudomorphic film indicating presence of rhombohedral distortion in this direction. Polar Kerr effect and ferromagnetic resonance measurements showed existence of additional magnetic anisotropy, which adds to the demagnetizing field to keep magnetization vector in the film plane. The origin of the magnetic anisotropy is related to the strain in YIG films observed by XRD. Magneto-optical Kerr effect measurements revealed important role of magnetization rotation during magnetization reversal. An unusual fine structure of microwave magnetic resonance spectra has been observed in the film grown at reduced (0.5 mTorr) oxygen pressure. Surface spin wave propagation has been demonstrated in the in-plane magnetized films.

We describe synthesis of submicron Y3Fe5O12 (YIG) films sputtered on Si substrates and present results of the investigation of ferromagnetic resonance (FMR) and spin waves in YIG/SiO2/Si structures. It is found that decrease of the annealing time leads to essential reduction of the FMR linewidth ΔH and, consequently, to reduction of relaxation losses of spin waves. Spin-wave propagation in in-plane magnetized YIG/SiO2/Si structures is studied. We observe the asymmetry of amplitude-frequency characteristics of the Damon-Eshbach spin waves caused by different localizations of spin waves at the free YIG surface and at the YIG/SiO2 interface. Growth of the generating microwave power leads to spin-wave instability and changes amplitude-frequency characteristics of spin waves.