arXiv subjects

A. Yu. Rusanov

Publications and source records attributed to A. Yu. Rusanov.

7 recordsLinked to original sources

arXiv2011

With no Color and Scent (part II): Metal and Alloy Microstructures-Handmade Replicas of Natural Objects

As a continuation of work on metal and alloy "plants" synthesis on porous membranes by means of pulsed current electroplating volume metallic microstructures resembling such natural objects as shells, cabbage leaves, mushrooms are grown and presented in their modest elegance. Such structures are formed from PdNi and PdCo alloys as well as Ag, Cu and Ni in conditions defined by the shape of membrane pores and the parameters of the pulsed current. It is shown that the obtained complex structures are formed by layers of metallic nanowires as a result of their self-assembly while growing during the pulsed current electroplating process. Depending on the shape of the membrane and the regime of the pulsed current electroplating either one type of shell-like structures or various structures can be grown.

cond-mat.mtrl-sci↗

arXiv2008

Observation of the magnetic domain structures in Cu$_{0,47}$Ni$_{0,53}$ thin films at low temperatures

We report on the first experimental visualization of domain structure in films of weakly ferromagnetic Cu$_{0,47}$Ni$_{0,53}$ alloy with different thickness at liquid helium temperatures. Improved high-resolution Bitter decoration technique was used to map the magnetic contrast on the top of the films well below the Curie temperature T$_{Curie}$ ($\sim$ 60 K). In contrast to magnetic force microscopy, this technique allowed visualization of the domain structure without its disturbance while the larger areas of the sample were probed. Maze-like domain patterns, typical for perpendicular magnetic anisotropy, were observed. The average domain width was found to be about 100 nm.

cond-mat.mtrl-sci↗

arXiv2005

Inverse spin switch effects in Ferromagnet / Superconductor hybrids with strong ferromagnets

In F/S/F trilayers where the magnetization directions of the F layers can be controlled separately, it has theoretically been predicted that the antiparallel (AP) configuration can have a higher superconducting transition temperature T_c than the parallel configuration. This is the so-called spin switch, which also experimentally has been found for the case of weak ferromagnets. Here we show that strong ferromagnets yield the opposite effect. We study the transport properties of F/S/F trilayers with F = Ni_0.80Fe_0.20 (Permalloy, Py) and S = Nb, structured in strips of different sizes. Using two different thicknesses for the Py layers, we can switch in a well-defined way between the AP- and P-configurations. In the superconducting transition we find a clear increase of the resistance in the AP-state. We ascribe this to enhanced reflection of spin-polarized quasiparticles at the S/F interfaces which leads to a stronger suppression of superconductivity on the S-side.

cond-mat.supr-con↗

arXiv2004

Enhancement of the superconducting transition temperature in Nb/Permalloy bilayers by controlling the domain state of the ferromagnet

In (S/F) hybrids the suppression of superconductivity by the exchange field h_ex of the ferromagnet can be partially lifted when different directions of h_ex are sampled simultaneously by the Cooper pair. In F/S/F trilayer geometries where the magnetization directions of the two F-layers can be controlled separately, this leads to the so-called spin switch. Here we show that domain walls in a single F-layer yield a similar effect. We study the transport properties of Ni_0.8Fe_0.2/Nb bilayers structured in strips of different sizes. For large samples a clear enhancement of superconductivity takes place in the resistive transition, in the very narrow field range (order of 0.5 mT) where the magnetization of the Py layer switches and many domains are present. This effect is absent in microstructured samples. Comparison of domain wall width δ_w to the temperature dependent superconductor coherence length ξ_S(T) shows that δ_w ~ ξ_S(T), which means that the Cooper pairs sample a large range of different magnetization directions.

cond-mat.supr-con↗

arXiv2003

Depairing currents in superconducting films of Nb and amorphous MoGe

We report on measuring the depairing current J_{dp} in thin superconducting films as a function of temperature. The main difficulties in such measurements are that heating has to be avoided, either due to contacts, or to vortex flow. The latter is almost unavoidable since the sample cross-section is usually larger than the superconducting coherence length ξ_s and the magnetic field penetration depth λ_s. On the other hand, vortex flow is helpful since it homogenizes the distribution of the current across the sample. We used a pulsed current method, which allows to overcome the difficulties caused by dissipation and measured the depairing current in films of thin polycrystalline Nb (low λ_s, low specific resistance ρ) and amorphous Mo_{0.7}Ge_{0.3} (high λ_s, high ρ), structured in the shape of bridges of various width. The experimental values of J_{dp} for different bridge dimensions are compared with theoretical predictions by Kupriyanov and Lukichev for dirty limit superconductors. For the smallest samples we find a very good agreement with theory, over essentially the whole temperature interval below the superconducting critical temperature.

cond-mat.supr-con↗

arXiv2001

Intrinsically frustrated superconducting array of SFS π-junctions

We report a direct observation of the crossover of the superconductor- ferromagnet-superconductor (SFS) junctions to the π-state which manifests itself in the half-period shift of the external magnetic field dependence of the transport critical current in the triangular SFS arrays. It is associated with the appearance of spontaneous supercurrents in the array at zero external field, with the ground state degenerated with respect to the two possible current flow directions. In conventional Josephson arrays this state can be observed only by imposing frustrating external field equal to a half-integer number of magnetic quanta per cell.

cond-mat.supr-con↗

arXiv2000

Coupling of two superconductors through a ferromagnet : evidence for a pi-junction

We report measurements of the temperature dependence of the critical current in Josephson junctions consisting of conventional superconducting banks of Nb and a weakly ferromagnetic interlayer of a Cu$_x$Ni$_{1-x}$ alloy, with $x$ around 0.5. With decreasing temperature $I_c$ generally increases, but for specific thicknesses of the ferromagnetic interlayer, a maximum is found followed by a strong decrease down to zero, after which $I_c$ rises again. Such a sharp cusp can only be explained by assuming that the junction changes from a 0-phase state at high temperatures to a $π$-phase state at low temperatures.

cond-mat.supr-con↗