| 1. |
- Tarnavich, V., et al.
(author)
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Magnetic field induced chirality in Ho/Y multilayers with gradually decreasing anisotropy
- 2017
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:1
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Journal article (peer-reviewed)abstract
- Metal rare-earth magnetic/nonmagnetic Ho/Y superlattice structures possess a coherent spin helix propagating through many superlattice layer repetitions. An externalmagnetic field applied in the film plane induces a nonzero average chirality of the helices. It is shown that the direction of the applied in-plane field can modify the value and sign of the chirality parameter.. The dependence of. on the relative angle of applied field during the field`-cooling procedure has an oscillatory character and can be described by simple sinusoidal function with p periodicity. The experimental finding is discussed from the point of view of an interbalance between Zeeman energy, magnetocrystalline anisotropy, and induced uniaxial anisotropy.
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| 2. |
- Suturin, S. M., et al.
(author)
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Role of gallium diffusion in the formation of a magnetically dead layer at the Y3Fe5O12/Gd3Ga5O12 epitaxial interface
- 2018
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In: PHYSICAL REVIEW MATERIALS. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:10
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Ukleev, V., et al.
(author)
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Morphology and magnetic properties of nanocomposite magnetic multilayers [(Co(4)oFe(40)B(2)O)(34)(SiO2)(66)]/[C](47)
- 2016
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In: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 432, s. 499-504
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Journal article (peer-reviewed)abstract
- We report on the investigation of morphology, magnetic and conductive properties of the mutilayered nanostructures [(Co40Fe40B20)(34)(SiO2)(66)]/[C](47) consisting of the contacting magnetic (Co Fe-40 (40) B (20)) (34)(SiO2)(66) nanocomposite and amorphous semiconductor carbon C layers. It is shown by Grazing-Incidence Small-Angle X-ray Scattering method that the ordering and the size of nanoparticles in the magnetic layers do not change profoundly with increasing of carbon layer thickness. Meanwhile, the electrical conductance and the magnetic properties are significantly varied: resistance of the samples changes by four orders of magnitude and superparamagnetic blocking temperature changes from 15 K to 7 K with the increment of carbon layer thickness h(c) from 0.4 nm to 1.8 nm. We assume that the formation of the homogeneous semiconductor interlayer leads to modification of the metal-insulator growth process that drives the changes in the magnetic and conductive properties.
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| 4. |
- Ukleev, V, et al.
(author)
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Coherent charge and magnetic ordering in Ho/Y superlattice revealed by element-selective x-ray scattering
- 2019
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 100:13
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Journal article (peer-reviewed)abstract
- Magnetic rare-earth/nonmagnetic metal superlattices are well-known to display chiral spin helices in the rare-earth layers that propagate coherently across the nonmagnetic layers. However, the underlying mechanism that preserves the magnetic phase and chirality coherence across the nonmagnetic layers has remained elusive. In this paper, we use resonant and element-specific x-ray scattering to evidence directly the formation of two fundamentally different long-range modulations in a holmium/yttrium (Ho/Y) multilayer: the known Ho chiral spin helix with periodicity 25 angstrom and a newly observed charge density wave with periodicity 16 angstrom that propagates through both the Ho and nonmagnetic Y layer. With x-ray circular magnetic dichroism measurements ruling out the existence of a magnetic proximity effect induced moment in the nonmagnetic Y layers, we propose that the charge density wave is also chiral, thus providing the means for the transmittance of magnetic chirality coherence between Ho layers.
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| 5. |
- Ukleev, V., et al.
(author)
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Imprinted Magnetic Anisotropy and Zigzag Domain Structure of Amorphous TbCo Films
- 2015
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In: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1939 .- 1557-1947. ; 28:12, s. 3571-3577
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Journal article (peer-reviewed)abstract
- We investigate the magnetic anisotropy and domain structure of amorphous Tb (x) Co(1-x) films grown in external in-plane magnetic field by high-frequency ion sputtering. Films with different thicknesses 100 and 500 nm and rare-earth element concentrations x = 12 % and x = 34 % present strong imprinted in-plane uniaxial anisotropy. Measurements of magnetic properties and domain structure imaging were performed by means of longitudinal and polar magneto-optical Kerr effect (MOKE). The coercivity fields increase by an order of magnitude for the higher Tb concentration and increase with film thickness (H (c) along the hard axis are 495, and 580 Oe, for 100 and 500 nm, with x = 34 % and 65, and 95 Oe for 100 and 500 nm with x = 12 %, respectively). Polar MOKE measurements revealed the existence of an out-of-plane magnetization component for the films with a Tb concentration of 34 % in lower fields. Large-scale domain structure of TbCo films with imprinted anisotropy was also studied as a function of applied field. Kerr imaging shows a zigzag domain structure of Tb12Co88 films, while no domains were found in Tb34Co66 samples. We also demonstrate that the zigzag angle depends on the film thickness. We suggest that domain structure in these films is determined by the interplay of imprinted and local magnetic anisotropies as well as exchange interaction.
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| 6. |
- Grigoryeva, Natalia A., et al.
(author)
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Mesostructure and Magnetic Properties of SiO2-Co Granular Film on Silicon Substrate
- 2022
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In: MAGNETOCHEMISTRY. - : MDPI. - 2312-7481. ; 8:12
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Journal article (peer-reviewed)abstract
- Granular films SiO2(Co) exhibit unusual magnetic and magnetotransport properties which are strongly dependent on the composition of the film and material of a substrate. For example, the injection magnetoresistance (IMR) coefficient reaches a giant (GIMR) value of 10(5)% at room temperature in SiO2(Co) films on an n-GaAs substrate. However, the IMR effect is negligible in the case of a similar granular film deposited on the n-Si substrate. In this report, the structural and magnetic properties of granular film SiO2(Co) on Si substrate are studied with the aim to understand the cause of the difference in IMR coefficients for SiO2(Co) thin film deposited on n-GaAs and on n-Si substrates. Investigations were carried out using complementary methods of Polarized Neutron Reflectometry, Grazing Incidence Small-Angle X-ray Scattering, X-ray Reflectometry, Scanning Electron Microscope, and SQUID magnetometry. It is shown that the interface layer between the granular film and Si substrate exhibits metallic rather than magnetic properties and eliminates the GIMR effect. This interface layer is associated with the Si diffusion to Co nanoparticles and the formation of the metallic cobalt silicides.
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| 7. |
- Magnus, Fridrik, et al.
(author)
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Sequential magnetic switching in Fe/MgO(001) superlattices
- 2018
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 97:17
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Journal article (peer-reviewed)abstract
- Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchangecoupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90◦periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the toplayer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180◦periodic alignment isobtained at remanence and with increasing applied field the layer switching starts from the two outermost layersand proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensionalmagnetic structures with a predefined discrete switching sequence
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| 8. |
- Moubah, Reda, et al.
(author)
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Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
- 2016
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In: Physical Review Applied. - : American physical society. - 2331-7019. ; 5:4
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Journal article (peer-reviewed)abstract
- We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.
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| 9. |
- Ukleev, V., et al.
(author)
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Polarized neutron reflectometry study from iron oxide nanoparticles monolayer
- 2017
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In: SURFACES AND INTERFACES. - : ELSEVIER SCIENCE BV. - 2468-0230. ; 9, s. 143-146
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Journal article (peer-reviewed)abstract
- We report on the polarized neutron reflectometry investigation of monolayer of magnetic iron oxide nanoparticles assembled by the Langmuir-Schaefer method. After deposition onto a solid substrate the polarized neutron reflectometry measurements in the external magnetic field were carried out. Thickness, density, roughness and in-depth resolved magnetization profile of the resulted layer were obtained from accurate fitting routine.
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| 10. |
- Ukleev, V., et al.
(author)
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Self-assembly of a binary mixture of iron oxide nanoparticles in Langmuir film : X-ray scattering study
- 2017
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In: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 202, s. 31-39
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Journal article (peer-reviewed)abstract
- In present study we exploited Langmuir technique to produce self-assembled arrays composed of monodisperse iron oxide nanoparticles 10 nm and 20 nm in diameter and of their binary mixture. A combination of in-situ X-ray reflectometry and Grazing-incident small-Angle X-ray scattering was used to obtain in-plane and out-of-plane structure of the arrays directly on the water surface. Surface pressure isotherms and X-ray reflectometry analysis showed that monodisperse 10 nm nanoparticles form a highly ordered monolayer, while 20 nm particles pack in three-dimensional clusters with a short-range (nearest-neighbor) correlations between the particles. In a binary mixture of 10 nm and 20 nm nano particles composed in proportion 3:1 the self-assembly process results in a structure where the monolayer of 10 nm particles is perturbed by the larger particles. Non-trivial mixing causes an enlargement of interparticle distance but keeps the symmetry of two-dimensional lattice of smaller nanoparticles. Estimation of the acting interactions and micromagnetic simulation suggest the optimal formation for monodisperse and binary ensembles.
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| 11. |
- Ukleev, V., et al.
(author)
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X-ray scattering characterization of iron oxide nanoparticles Langmuir film on water surface and on a solid substrate
- 2016
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 616, s. 43-47
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Journal article (peer-reviewed)abstract
- In the present study we compare a structure of a Langmuir film assembled from magnetic iron oxide nanoparticles on water surface and a structure of the same film after its transfer to a solid substrate by the Langmuir-Schaefer method. In contrast to most of related studies, where different techniques are used to characterize the films before and after the deposition, we use the same combination of X-ray reflectometry and Grazing Incidence Small-Angle X-ray scattering. In both cases - on a liquid and on a solid substrate - the film was identified as a well-ordered monolayer of the nanoparticles laterally organized in a two-dimensional hexagonal lattice. However parameters of the lattice were found to be slightly different depending on the type of the substrate. It is also demonstrated that Langmuir-Schaefer technique is the right way for deposition of such kind of the particles on a solid substrate.
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| 12. |
- Vorobiev, Alexey, et al.
(author)
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Substantial Difference in Ordering of 10, 15, and 20 nm Iron Oxide Nanoparticles on a Water Surface : In Situ Characterization by the Grazing Incidence X-ray Scattering
- 2015
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 31:42, s. 11639-11648
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Journal article (peer-reviewed)abstract
- In the present study, for the first time, a unique combination of in situ grazing incidence small-angle X-ray scattering and X-ray reflectivity, accompanied by the pressure area isotherm analysis, Brewster angle microscopy, and ex situ scanning electron microscopy, was applied for investigation of two-dimensional superlattices of magnetic nanoparticles as they form on a water surface in a Langmuir trough. Iron oxide particles of different sizes stabilized with a single layer of oleic acid were used. It is demonstrated that monodisperse 10 nm particles on a water surface reproducibly form identical highly ordered monolayers in a wide range of experimental conditions, while monodisperse 20 nm particles always form compact three-dimensional clusters and never the monolayers. Monodisperse particles of an intermediate size, 15 um in diameter, build a metastable monolayer, which shows a tendency for spontaneous transformation to bi-, tri-, and multilayer islands. The importance to use both grazing incidence small-angle X-ray scattering and X-ray reflectivity together with the complementary techniques, to avoid misinterpretation of separate experimental data sets, is underlined.
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