The magnetization in a superconductor induced due to the inverse proximity effect is investigated in hybrid bilayers containing a superconductor and a ferromagnetic insulator or a strongly ...spin-polarized ferromagnetic metal. The study is performed within a quasiclassical Green function framework, wherein Usadel equations are solved with boundary conditions appropriate for strongly spin-polarized ferromagnetic materials. A comparison with recent experimental data is presented. The singlet to triplet conversion of the superconducting correlations as a result of the proximity effect with a ferromagnet is studied.
Abstract
The present study investigates the behavior of the Cooper pair wave function in a normal metal (NM) near superconductor-NM-junctions, specifically focusing on the ballistic regime at zero ...temperature. It is widely assumed that the wave function follows a power-law decay, with the decay exponents dependent on the system’s dimensionality. Our work reveals that the multiband nature of a compound significantly influences the damping degree of pair amplitudes in an NM, rendering it sensitive to the position of the Fermi level. To explore this phenomenon, we employ the numerical method of self-consistent Bogoliubov–de Gennes equations, utilizing a nanowire as a model for an electronic multiband system. By analyzing the obtained pair amplitudes, we extract relevant lengths and exponents that characterize the leakage of superconducting correlations. We further examine this phenomenon by varying the sample’s cross-sectional size and the superconducting coupling constant. Consequently, our findings demonstrate that the properties of a superconducting/NM junction’s proximity effect can be manipulated not only through temperature, total impurity and defect density, but also by controlling the position of the Fermi level. This tunability enables the transition from a long-range regime to a short-range one, providing valuable insights for designing and understanding such junctions in practical applications.
The Cosmic Microwave Background (CMB) radiation is the only observable that allows studying the earliest stage of the Universe. Radioastronomy instruments for CMB investigation require low working ...temperatures around 100 mK to get the necessary sensitivity. On-chip electron cooling of receivers is a pathway for future space missions due to problems of dilution fridges at low gravity. Here, we demonstrate experimentally that in a Cold-Electron Bolometer (CEB) a theoretical limit of electron cooling down to 65 mK from phonon temperature of 300 mK can be reached. It is possible due to effective withdrawing of hot electrons from the tunnel barrier by double stock, special traps and suppression of Andreev Joule heating in hybrid Al/Fe normal nanoabsorber.
This work investigates the magnetization of a superconductor induced by the proximity effect in bilayers containing a superconductor and a ferromagnetic insulator using the Green’s functions method. ...The simulation was carried out using the quasi-classical approximation; the Usadel equations were solved using boundary conditions specially developed for strongly ferromagnetic materials. The suppression of the superconducting order parameter as a result of the effect of the proximity to the ferromagnetic insulator has also been investigated.
This paper presents a theoretical study of the dynamics of the induced magnetization and spin current arising in a layer of an impure superconductor due to the proximity to a ferromagnetic dielectric ...with a uniform periodically precessing magnetization. The dynamics of the observed physical quantities is described within the semi-classical Usadel–Floquet formalism, which makes it possible to study the effect of a periodic perturbation on an inhomogeneous superconducting system. The spatial distributions and temporal evolution of the induced magnetization and the superconducting spin current inside the superconductor layer are found from the numerical solutions of the system of Usadel–Floquet equations.
The magnetization induced in a superconductor due to the reverse proximity effect is studied in hybrid structures containing a superconductor and a ferromagnetic insulator. The study was carried out ...within the method of semiclassical Green’s functions, in which the Usadel equations are solved numerically with boundary conditions suitable for strongly spin-polarized ferromagnetic materials. The conversion of singlet superconducting correlations into triplet ones as a result of the proximity effect with a ferromagnet and its manifestation in the features of the electron density of states, induced magnetization, and suppression of the superconducting order parameter have been studied. It is shown that the magnetization can change sign inside the superconducting layer. The magnetization distribution is compared with the data obtained by the authors in previous works.
The influence of a large spin-polarized current on the coupled dynamics of vortices in spin-transfer nanooscillators with a diameter of 400 nm is investigated. New stationary modes of coupled ...oscillations of vortices have been discovered, both for the same and opposite polarities of their cores. The dependence of the frequency of stationary coupled oscillations of magnetic vortices on the magnitude of the spin-polarized current has been studied. The found effect can be used to increase the operating frequencies of spin-transfer nano-oscillators.
The structure and magnetization dynamics are investigated in a vortex spin-transfer nanooscillator, which is a three-layer spin-valve magnetic nanocolumn with a large diameter of 400 nm, under ...flowing spin-polarized current through it. The dynamic variation in the structure of vortices and their trajectory of motion are studied, using micromagnetic modeling, as a function of the value of the spin-polarized current. It is demonstrated that different modes of motion of vortices may exist: decaying oscillations of vortices, stationary oscillations of vortices, and the mode of switching polarity of one of vortices. The time for which different dynamic modes are settled is determined. The dependence of the oscillation frequency on the value of spin-polarized current is determined for the case of stationary dynamics of coupled vortices. It is shown that, at large values of current, switching of vortex polarity is only possible in a thick layer with the dynamic switching mechanism accompanied by generation of a vortex–antivortex pair. The software package for micromagnetic simulation, SpinPM, is used for numerical calculations of the dynamics of magnetic vortices.
Using the Usadel approach, we provide a formalism that allows us to calculate the critical current density of 21 different types of Josephson junctions (JJs) with a ferromagnetic (F) barrier and ...additional insulating (I) or/and normal (N) layers inserted between the F layer and superconducting (S) electrodes. In particular, we obtain that in SFS JJs, even a thin additional N layer between the S layer and F layer may noticeably change the thickness \({d}_{{\rm{F}}}\) of the F layer at which the 0-π transitions occur. For certain values of \({d}_{{\rm{F}}},\) a 0-π transition can even be achieved by changing only the N layer thickness. We use our model to fit experimental data of SIFS and SINFS tunnel junctions.
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