•The magneto-impedance of a CoP@Cu core–shell microwire was investigated.•The long term stability of the CoP metallic amorphous alloy was tested.•A microstrip waveguide was used for measuring the ...magneto-impedance.•Giant magneto-impedance effect yielded values as high as 98 % for f = 30 MHz.•The Kittel formula for a plate geometry accounted for FMR in the microwave regime.
The giant magneto-impedance effect (GMI) consists in a large variation in the electrical impedance that occurs in some magnetic materials when subjected to a variable external magnetic field. Here we present an experimental study of the GMI in a wide frequency range observed in a structure of the metallic amorphous magnetic alloy CoP electrodeposited on copper microwires by using a microstrip configuration. In the low frequency range, the magnetic field dependence of the impedance is due to the behavior of the circumferential ac susceptibility in the magnetic coating. In the microwave range the behavior of the GMI is dominated by the main dynamical magnetic phenomenon at high frequencies, namely ferromagnetic resonance (FMR). The experimental data are well fit by Kittel equation for the FMR frequency for a ferromagnetic layer with a saturation magnetization similar to the ones reported in previous works. The structural stability of the CoP alloy against aging effects was also investigated. The overall results indicate that the CoP alloy is a good candidate for applications in sensors and in microwave devices.
In this study, a series of Li0.43Zn0.27Ti0.13Fe2.17O4 ferrites were successfully synthesized by solid-state reaction method at 920 ℃ employing low melting point V2O5 as sintering aid. The X-ray ...diffraction (XRD) studies demonstrated that all samples exhibited spinel phase. Microscopic image analysis revealed that both the grain growth and uniformity were significantly promoted. The average grain size was increased from 0.65 µm to 4.53 µm when V2O5 was increased from 0.0 wt% to 2.4 wt%. In terms of the magnetic properties, the saturation magnetization (4πMs) of the samples increased from 2915 Gs to 3434 Gs, the coercivity (Hc) decreased from 848.3 A/m to 242.2 A/m, and the ferromagnetic resonance linewidth (ΔH) decreased from 963 Oe to 543 Oe. It could be noted that the proper addition of V2O5 is the key to optimizing the microstructure and magnetic properties of LiZnTi microwave ferrite. Therefore, as an effective additive, V2O5 can promote the development of low temperature co-fired ferrites.
•Microstructure of LiZnTi ferrite was improved by V2O5 doping. Grain growth and uniformity were obviously promoted.•Magnetic properties, including 4πMs and Hc, were optimized by V2O5 doping.•Ferromagnetic resonance linewidth (ΔH) was decreased significantly by V2O5 doping.
Control of the Magnon-Photon Coupling Lihui Bai; Blanchette, K.; Harder, M. ...
IEEE transactions on magnetics,
2016-July, 2016-7-00, 20160701, Letnik:
52, Številka:
7
Journal Article
A systematic study of the electrodynamic coupling between the ferromagnetic resonance (FMR) and the cavity mode of a microwave cavity is presented. The nature of the FMR and cavity modes, described ...by their resonance position and line width, is measured and compared with a classical model based on the Landau-Lifshitz-Gilbert equation and an RLC circuit, which explicitly implement Faraday's and Ampère's laws. The relationship between the coupling gap, which can be accessed experimentally, and the coupling strength, which is a fundamental property of the FMR/cavity system, is discussed on the basis of this model. A straightforward method is experimentally developed to control the coupling gap. The capability of using such a tunable cavity-FMR coupling in combination with spin pumping could provide us with new technologies that utilize the light-matter interaction to control spin current in cavity spintronics.
Remote epitaxial growth via a graphene interlayer and subsequent mechanical exfoliation of a free-standing membrane is a recently developed technique used to transfer complex oxide thin films onto ...non-native substrates to form heterogeneously integrated structures for various device applications. One such oxide is Yttrium Iron Garnet (YIG), a material of choice for a wide range of magnetoelectric and spintronic devices owing to its strong magnetic properties and low microwave losses. YIG is predominantly grown on lattice matched Gadolinium Gallium Garnet (GGG) substrates, but by utilizing the remote epitaxy technique, high quality YIG films can be transferred from GGG onto another substrate such as piezoelectric Lithium Niobate (LN). Mechanical strain coupling between the layers and magnetostrictive nature of YIG would allow for the investigation of the interplay in YIG/LN structures leading to the design of novel frequency agile magneto-acoustic devices. In this study functional properties of a YIG film grown using PLD on graphene-coated GGG substrate were investigated and compared to traditional YIG on GGG. Both materials were characterized in terms of crystal structure, surface morphology, FMR and Gilbert damping, and Raman and XAS spectroscopy. Further, it was found that YIG on graphene-coated GGG exhibits significantly higher microwave losses than standard YIG on GGG (FMR linewidth 30.9 vs 2.1 Oe at 10 GHz, and Gilbert damping coefficient 15.4x10-4 vs 3.4x10-4 respectively), which was attributed to increased concentration of Fe2+ cations in YIG/Graphene/GGG. While the damping is higher in these studied films compared to YIG grown directly on GGG, the resulting properties are still very favorable compared to many other competing materials which can be grown without the need for lattice matched substrates, such as metallic ferromagnets.
Major depressive disorder (MDD) is common and disabling, but its neuropathophysiology remains unclear. Most studies of functional brain networks in MDD have had limited statistical power and data ...analysis approaches have varied widely. The REST-meta-MDD Project of resting-state fMRI (R-fMRI) addresses these issues. Twenty-five research groups in China established the REST-meta-MDD Consortium by contributing R-fMRI data from 1,300 patients with MDD and 1,128 normal controls (NCs). Data were preprocessed locally with a standardized protocol before aggregated group analyses. We focused on functional connectivity (FC) within the default mode network (DMN), frequently reported to be increased in MDD. Instead, we found decreased DMN FC when we compared 848 patients with MDD to 794 NCs from 17 sites after data exclusion. We found FC reduction only in recurrent MDD, not in first-episode drug-naïve MDD. Decreased DMN FC was associated with medication usage but not with MDD duration. DMN FC was also positively related to symptom severity but only in recurrent MDD. Exploratory analyses also revealed alterations in FC of visual, sensory-motor, and dorsal attention networks in MDD. We confirmed the key role of DMN in MDD but found reduced rather than increased FC within the DMN. Future studies should test whether decreased DMN FC mediates response to treatment. All R-fMRI indices of data contributed by the REST-meta-MDD consortium are being shared publicly via the R-fMRI Maps Project.
Abstract We study the magnetic properties of arrays of Co nanowires which exhibit zero bias-field ferromagnetic resonance absorptions in a 0–30 GHz range. Columnar arrays of Co nanowires with lengths ...of 8–15 µ m were electrochemically grown using ∼20 µ m thick anodic alumina membranes with 50 nm pore diameters. Microstructural, static magnetic, and microwave properties of five different nanowire arrays were characterized. The studied Co nanowires present different crystal structure textures and magnetic properties. The static magnetic loop shapes and the ferromagnetic resonance frequencies of the nanowire arrays were correctly reproduced using the Mumax3 micromagnetic software. For each sample input parameters dependent on the x-ray diffraction and microstructural data, were fine-tuned to allow the best fit of the experimental hysteresis loops and the related microwave spectra. Using this method, it was possible to analyze the rather complex interplay between geometry and magneto-structural features of the different arrays, defining which parameters play a key role in the development of nano-systems with specific microwave properties.
•Dynamic magnetisation of trilayer systems with entirely different magnetic film materials.•Exemplary approach and illustration of spin currents facing a tunnel barrier and a step ...potential.•Theoretical and qualitative model calculation of a tunnel barrier and step potential combination.•Behaviour of enhanced and reduced precession damping due to spin current.
Ferromagnetic trilayer film systems with nonferromagnetic Si3N4 interface layers were fabricated by using magnetron sputtering. A post-annealing process was carried out at 400 °C for 2 h in a static magnetic field, in order to induce an in-plane uniaxial anisotropy. The present study introduces the exchange interaction between ferromagnetic layers which influences the static magnetisation properties as well as the natural resonance frequency behaviour and its damping features, i.e., damping and anti-damping effects. This is expressed by the total damping parameter αitot = αGi ± αspi, which is enhanced or reduced by a spin transfer torque damping parameter ± αspi whereupon Gilbert bulk damping αGi is considered to be independent. The static polarisation loops are slightly but noticeably different, caused by an interface with thickness up to 100 nm, which reflects a decreasing exchange interaction. With varying the interface thickness, the films also show a distinct variation in their frequency spectra. This leads to the conclusion that spin currents caused by spin pumping arise, and tunnelling within a Si3N4 insulating barrier generates spin transfer torque. This can be assumed because the observed ferromagnetic resonance dual lines show remarkable changes in their Full Width at Half Maxima (FWHM) at frequencies of approximately 600 MHz caused by the Ni80Fe20 layers and 2.32 GHz caused by the Fe40Co37Zr11N12 layers. Regarding the FWHM of the resonance frequency spectra in association with the damping constant αeff on the dependence of the interface layer thickness, one can observe an exponential curve shape for both ferromagnetic layers, which is obviously a sign for the interaction between the layers through a spin current tunnelling mechanism.
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