70 research outputs found
Reciprocal space mapping of magnetic order in thick epitaxial MnSi films
We report grazing incidence small angle neutron scattering (GISANS) and
complementary off-specular neutron reflectometry (OSR) of the magnetic order in
a single-crystalline epitaxial MnSi film on Si(111) in the thick film limit.
Providing a means of direct reciprocal space mapping, GISANS and OSR reveal a
magnetic modulation perpendicular to the films under magnetic fields parallel
and perpendicular to the film, where additional polarized neutron reflectometry
(PNR) and magnetization measurements are in excellent agreement with the
literature. Regardless of field orientation, our data does not suggest the
presence of more complex spin textures, notably the formation of skyrmions.
This observation establishes a distinct difference with bulk samples of MnSi of
similar thickness under perpendicular field, in which a skyrmion lattice
dominates the phase diagram. Extended x-ray absorption fine structure
measurements suggest that small shifts of the Si positions within the
unstrained unit cell control the magnetic state, representing the main
difference between the films and thin bulk samples
Evidence for spin-triplet superconducting correlations in metal-oxide heterostructures with non-collinear magnetization
Heterostructures composed of ferromagnetic La0.7Sr0.3MnO3, ferromagnetic
SrRuO3, and superconducting YBa2Cu3Ox were studied experimentally. Structures
of composition Au/La0.7Sr0.3MnO3/SrRuO3/YBa2Cu3Ox were prepared by pulsed laser
deposition, and their high quality was confirmed by X-ray diffraction and
reflectometry. A non-collinear magnetic state of the heterostructures was
revealed by means of SQUID magnetometry and polarized neutron reflectometry. We
have further observed superconducting currents in mesa-structures fabricated by
deposition of a second superconducting Nb layer on top of the heterostructure,
followed by patterning with photolithography and ion-beam etching. Josephson
effects observed in these mesa-structures can be explained by the penetration
of a triplet component of the superconducting order parameter into the magnetic
layers.Comment: 10 pages, 6 figure
Magnetic proximity effect at interface between a cuprate superconductor and an oxide spin valve
Heterostructures consisting of a cuprate superconductor YBa2Cu3O7x and a
ruthenate/manganite (SrRuO3/La0.7Sr0.3MnO3) spin valve have been studied by
SQUID magnetometry, ferromagnetic resonances and neutron reflectometry. It was
shown that due to the influence of magnetic proximity effect a magnetic moment
is induced in the superconducting part of heterostructure and at the same time
the magnetic moment is suppressed in the ferromagnetic spin valve. The
experimental value of magnetization induced in the superconductor has the same
order of magnitude with the calculations based on the induced magnetic moment
of Cu atoms due to orbital reconstruction at the superconductor-ferromagnetic
interface. It corresponds also to the model that takes into account the change
in the density of states at a distance of order of the coherence length in the
superconductor. The experimentally obtained characteristic length of
penetration of the magnetic moment into superconductor exceeds the coherence
length for cuprate superconductor. This fact points on the dominance of the
mechanism of the induced magnetic moment of Cu atoms due to orbital
reconstruction.Comment: 20 pages, 9 figure
Magnetic proximity effects in V/Fe superconductor/ferromagnet single bilayer revealed by waveguide-enhanced polarized neutron reflectometry
Polarized neutron reflectometry is used to study the magnetic proximity
effect in a superconductor/ferromagnet (SC/FM) system of composition
Cu(32nm)/V(40nm)/Fe(1nm)/MgO. In contrast to previous studies, here a single
SC/FM bilayer, is studied and multilayer artefacts are excluded. The necessary
signal enhancement is achieved by waveguide resonance, i.e. preparing the
V(40nm)/Fe(1nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate
and Cu top layer, respectively . A new magnetic state of the system was
observed at temperatures below 0.7 TC. manifested in a systematic change in the
height and width of the waveguide resonance peak. Upon increasing the
temperature from 0.7 TC to TC, a gradual decay of this state is observed,
accompanied by a 5% growth of the diffuse scattering. According to theoretical
studies, such behavior is the result of the magnetic proximity effect. Due to
the presence of the thin FM layer the superconducting electrons are polarized
and, as a result, near the SC/FM interface an additional magnetic layer appears
in the SC with thickness comparable to ksi, the coherence length of the
superconductor.Comment: Submitted to the Journal of Superconductivity and Novel Magnetism. 11
pages, 6 figures
Element-Specific Depth Profile of Magnetism and Stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 Interface
Depth-sensitive magnetic, structural and chemical characterization is
important in the understanding and optimization of novel physical phenomena
emerging at interfaces of transition metal oxide heterostructures. In a
simultaneous approach we have used polarized neutron and resonant X-ray
reflectometry to determine the magnetic profile across atomically sharp
interfaces of ferromagnetic La0.67Sr0.33MnO3 / multiferroic BiFeO3 bi-layers
with sub-nanometer resolution. In particular, the X-ray resonant magnetic
reflectivity measurements at the Fe and Mn resonance edges allowed us to
determine the element specific depth profile of the ferromagnetic moments in
both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a
magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in
contrast to previous observations on inversely deposited layers. Additional
resonant X-ray reflection measurements indicate a region of an altered Mn- and
O-content at the interface, with a thickness matching that of the magnetic
diluted layer, as origin of the reduction of the magnetic moment.Comment: 13 pages, 4 figures, supplemental material include
Effect of Cr spacer on structural and magnetic properties of Fe/Gd multilayers
In this work we analyse the role of a thin Cr spacer between Fe and Gd layers
on structure and magnetic properties of a [Fe(35A)/Cr(tCr)/Gd(50A)/Cr(tCr)]x12
superlattice. Samples without the Cr spacer (tCr=0) and with a thin tCr=4A are
investigated using X-ray diffraction, polarized neutron and resonance X-ray
magnetic reflectometry, SQUID magnetometery, magneto-optical Kerr effect and
ferromagnetic resonance techniques. Magnetic properties are studied
experimentally in a wide temperature range 4-300K and analysed theoretically
using numerical simulation on the basis of the mean-field model. We show that a
reasonable agreement with the experimental data can be obtained considering
temperature dependence of the effective field parameter in gadolinium layers.
The analysis of the experimental data shows that besides a strong reduction of
the antiferromagnetic coupling between Fe and Gd, the introduction of Cr
spacers into Fe/Gd superlattice leads to modification of both structural and
magnetic characteristics of the ferromagnetic layers
Magnetic ordering in Fe/X/Gd (X=Cr, Pd) superlattices
We have studied the influence Cr and Pd spacers on structure and magnetic ordering in Fe/Gd superlattices. The insertion of Cr and Pd spacers in Fe/Gd has been found to cause structural changes in Gd layers. In particular, an additional fcc Gd phase appears in Fe/Cr/Gd along with the main hcp Gd phase, while there is amorphous Gd structure in Fe/Pd/Gd. By combining SQUID magnetometry and polarized neutron reflectometry we have shown that interlayer Fe-Gd exchange coupling through Pd spacers is much stronger than through Cr one. © Published under licence by IOP Publishing Ltd.Russian Foundation for Basic Research, RFBR: 18-32-00197, 19-02-00674Ministry of Education and Science of the Russian Federation, Minobrnauka: AAAA-A18-118020290104-2The results were obtained within the state assignment of Ministry of Education and Science of Russia (subject “Spin” AAAA-A18-118020290104-2) and in part supported by the Russian Foundation for Basic Research (projects Nos. 18-32-00197 and 19-02-00674)
On the explanation of the paramagnetic Meissner effect in superconductor/ferromagnet heterostructures
An increase of the magnetic moment in superconductor/ferromagnet (S/F) bilayers V(40nm)/F [F=Fe(1,3nm), Co(3nm), Ni(3nm)] was observed using SQUID magnetometry upon cooling below the superconducting transition temperature TC in magnetic fields of 10 Oe to 50 Oe applied parallel to the sample surface. A similar increase, often called the paramagnetic Meissner effect (PME), was observed before in various superconductors and superconductor/ferromagnet systems. To explain the PME effect in the presented S/F bilayers a model based on a row of vortices located at the S/F interface is proposed. According to the model the magnetic moment induced below TC consists of the paramagnetic contribution of the vortex cores and the diamagnetic contribution of the vortex-free region of the S layer. Since the thickness of the S layer is found to be 3-4 times less than the magnetic field penetration depth, this latter diamagnetic contribution is negligible. The model correctly accounts for the sign, the approximate magnitude and the field dependence of the paramagnetic and the Meissner contributions of the induced magnetic moment upon passing the superconducting transition of a ferromagnet/superconductor bilayer
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