arXiv subjects

S. Sergeenkov

Publications and source records attributed to S. Sergeenkov.

At least 19 recordsLinked to original sources

arXiv2018

Quantum Ring in Gapped Graphene Layer with Wedge Disclination in the Presence of an Uniform Magnetic Field

In this paper we investigate the relativistic quantum dynamics of a massive excitation in a graphene layer with a wedge disclination in the presence of an uniform magnetic field. We use a Dirac oscillator type coupling to introduce the confining potential for massive fermions in this system. We obtain the energy spectrum and eigenfunctions for the quantum ring pierced by Aharonov-Bohm flux resulting in appearance of persistent current and spontaneous magnetization.

cond-mat.mes-hall↗

arXiv2018

Comparative study on magnetoresistance of carbon-cobalt nanocomposite thin films grown by pulsed laser deposition

We present a comparative study on the influence of applied magnetic field on the resistance of $C_{1-x}Co_x$ thin films (with $x=0.1$, $0.15$ and $0.2$) grown on $Si$ substrate by pulsed laser deposition technique. It is found that the behavior of magnetoresistance (MR) drastically depends on the temperature. Namely, at low temperatures MR is positive and its behavior is governed by the field mediated weak localization scenario. While at high temperatures MR turns negative and its behavior is dominated by electron scattering on ferromagnetic cobalt atoms.

cond-mat.mtrl-sci↗

arXiv2017

Influence of substrate on structural and transport properties of LaNiO3 thin films prepared by pulsed laser deposition

We report the structural and transport properties of LaNiO3 thin films prepared by pulsed laser deposition technique. To understand the effects of film thickness, lattice mismatch and grain size on transport properties, various oriented substrates were used for deposition, including single-crystalline SrLaAlO4 (001), SrTiO3 (100) and LaAlO3 (100). To achieve a high quality LaNiO3 thin films, the vital parameters (such as laser fluence, substrate temperature, oxygen pressure, and deposition time) were optimized. The best quality films are found to be well textured samples with good crystalline properties.

cond-mat.mtrl-sci↗

arXiv2017

Deciphering M-T diagram of shape memory Heusler alloys: reentrance, plateau and beyond

We present our recent results on temperature behaviour of magnetization observed in Ni_47Mn_39In_14 Heusler alloys. Three regions can be distinguished in the M-T diagram: (I) low temperature martensitic phase (with the Curie temperature T_CM = 140 K), (II) intermediate mixed phase (with the critical temperature T_MS = 230 K) exhibiting a reentrant like behavior (between T_CM and T_MS) and (III) high temperature austenitic phase (with the Curie temperature T_CA = 320 K) exhibiting a rather wide plateau region (between T_MS and T_CA). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entire M-T diagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg-Landau scenario.

cond-mat.mtrl-sci↗

arXiv2017

Evidence for field induced proximity type behavior in ferromagnetic nanofluid

We report some unusual magnetic properties observed in CoFe2O4 based ferrofluid (with an average particle size of D = 6 nm). More precisely, in addition to the low-field ferromagnetic (FM) phase transition with an intrinsic Curie temperature T_Cb=350K, a second phase transition with an extrinsic Curie temperature T_Cw = 266K emerges at higher (saturating) magnetic field. The transitions meet at the crossover point T_cr = 210 K. The origin of the second transition is attributed to magnetic field induced proximity type interaction between FM particles through non-FM layers.

cond-mat.mtrl-sci↗

arXiv2017

Evolution of Landau levels in graphene-based topological insulators in the presence of wedge disclinations

In this paper we consider modification of electronic properties of graphene-based topological insulator in the presence of wedge disclination and magnetic field by adopting the Kane-Mele model with intrinsic spin-orbit coupling. Using the properly defined Dirac-Weyl equation for this system, an exact solution for the Landau levels is obtained. The influence of the topological defect on the evolution of Landau levels is discussed.

cond-mat.str-el↗

arXiv2017

Analogue of the quantum Hall effect for neutral particles with magnetic dipole moment

In this paper we investigate a possibility for the existence of an analog of the Quantum Hall Effect for neutral particles with a permanent magnetic moment $μ$ in the presence of crossed inhomogeneous magnetic and electric fields. We predict the appearance of Hall conductivity $σ_H=(e^2/h)ν(μ)$ with the Landau filling factor $ν(μ)\propto μ^2$. The estimates of the model parameters suggest quite an optimistic possibility to experimentally verify this prediction in optically trapped clouds of atomic BEC.

cond-mat.str-el↗

arXiv2015

Evidence for resonant scattering of electrons by spin fluctuations in $LaNiO_3/LaAlO_3$ heterostructures grown by pulsed laser deposition

We present measurements of resistivity $ρ$ in highly oriented $LaNiO_3$ films grown on $LaAlO_3$ substrates by using a pulsed laser deposition technique. The experimental data are found to follow a universal $ρ(T) \propto T^{3/2}$ dependence for the entire temperature interval ($20K<T<300K$). The observed behavior has been attributed to a resonant scattering of electrons on antiferromagnetic fluctuations (with a characteristic energy $\hbar ω_{sf}\simeq 2.1meV$) triggered by spin-density wave propagating through the interface boundary of $LaNiO_3/LaAlO_3$ sandwich.

cond-mat.mtrl-sci↗

arXiv2013

Analog of Fishtail Anomaly in Plastically Deformed Graphene

By introducing a strain rate generated pseudo-electric field, we discuss a magnetic response of a plastically deformed graphene. Our results demonstrate the appearance of dislocation induced paramagnetic moment in a zero applied magnetic field. More interestingly, it is shown that in the presence of the magnetoplastic effect, the resulting magnetization exhibits typical features of the so-called fishtail anomaly (previously observed in superconductors). The estimates of the model parameters suggest quite an optimistic possibility to experimentally realize the predicted phenomena in plastically deformed graphene.

cond-mat.mes-hall↗

arXiv2012

On Field Induced Diaelastic Effect in a Small Josephson Contact

An analog of the diaelastic effect is predicted to occur in a small Josephson contact with Josephson vortices manifesting itself as magnetic field induced softening of the contact shear modulus C(T,H). In addition to Fraunhofer type field oscillations, C(T,H) is found to exhibit pronounced flux driven temperature oscillations near T_C.

cond-mat.supr-con↗

arXiv2010

Pinning of spiral fluxons by giant screw dislocations in YBa_2Cu_3O_7 single crystals: Josephson analog of the fishtail effect

By using a highly sensitive homemade AC magnetic susceptibility technique, the magnetic flux penetration has been measured in YBa_2Cu_3O_7 single crystals with giant screw dislocations (having the structure of the Archimedean spirals) exhibiting a=3 spiral turnings, the pitch b=18.7 microns and the step height c=1.2nm (the last parameter is responsible for creation of extended weak-link structure around the giant defects). The magnetic field applied parallel to the surface enters winding around the weak-link regions of the screw in the form of the so-called spiral Josephson fluxons characterized by the temperature dependent pitch b_f(T). For a given temperature, a stabilization of the fluxon structure occurs when b_f(T) matches b (meaning an optimal pinning by the screw dislocations) and manifests itself as a pronounced low-field peak in the dependence of the susceptibility on magnetic field (applied normally to the surface) in the form resembling the high-field (Abrikosov) fishtail effect.

cond-mat.supr-con↗

arXiv2010

Universal R-C crossover in current-voltage characteristics for unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions

We report on some unusual behavior of the measured current-voltage characteristics (CVC) in artificially prepared two-dimensional unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions. The obtained nonlinear CVC are found to exhibit a pronounced (and practically temperature independent) crossover at some current I_{cr}=\left(\frac{1}{2β_C}-1\right)I_C from a resistance R dominated state with V_R=R\sqrt{I^2-I_C^2} below I_{cr} to a capacitance C dominated state with V_C=\sqrt{\frac{\hbar}{4eC}} \sqrt{I-I_C} above I_{cr}. The origin of the observed behavior is discussed within a single-plaquette approximation assuming the conventional RSJ model with a finite capacitance and the Ambegaokar-Baratoff relation for the critical current of the single junction.

cond-mat.supr-con↗

arXiv2010

Manifestation of geometric resonance in current dependence of AC susceptibility for unshunted array of Nb-AlOx-Nb Josephson junctions

A pronounced resonance-like structure has been observed in the current dependence of AC susceptibility for two-dimensional array of unshunted Nb-AlOx-Nb Josephson junctions. Using a single-plaquette approximation, we were able to successfully fit our data assuming that resonance structure is related to the geometric (inductive) properties of the array.

cond-mat.supr-con↗

arXiv2009

Manifestation of finite temperature size effects in nanogranular magnetic graphite

In addition to the double phase transition (with the Curie temperatures T_C=300K and T_{Ct}=144K), a low-temperature anomaly in the dependence of the magnetization is observed in the bulk magnetic graphite (with an average granular size of L=10nm), which is attributed to manifestation of the size effects below the quantum temperature. The best fits of the high-temperature data (using the mean-field Curie-Weiss and Bloch expressions) produced reasonable estimates for the model parameters, such as defects mediated effective spin exchange energy J=12meV (which defines the intragranular Curie temperature T_C) and proximity mediated interactions between neighboring grains (through potential barriers created by thin layers of non-magnetic graphite) with energy J_t=exp(-d/s)J=5.8meV (which defines the intergranular Curie temperature T_{Ct}) with d=1.5nm and s=2nm being the intergranular distance and characteristic length, respectively.

cond-mat.mtrl-sci↗

arXiv2009

Synthesis, characterization and magnetic properties of room-temperature nanofluid ferromagnetic graphite

We report the chemical synthesis route, structural characterization, and physical properties of nanofluid magnetic graphite (NFMG) obtained from the previously synthesized bulk organic magnetic graphite (MG) by stabilizing the aqueous ferrofluid suspension with an addition of active cationic surfactant. The measured magnetization-field hysteresis curves along with the temperature dependence of magnetization confirmed room-temperature ferromagnetism in both MG and NFMG samples.

cond-mat.mtrl-sci↗

arXiv2009

Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite

We report on unusual magnetic properties observed in the nanofluid room-temperature ferromagnetic graphite (with an average particle size of l=10nm). More precisely, the measured magnetization exhibits a low-temperature anomaly (attributed to manifestation of finite size effects below the quantum temperature) as well as pronounced temperature oscillations above T=50K (attributed to manifestation of the hard-sphere type pair correlations between ferromagnetic particles in the nanofluid).

cond-mat.mtrl-sci↗

arXiv2009

Unusually strong coherent response from grain-boundary Josephson network in polycrystalline Pr_{x}Y_{1-x}Ba_2Cu_3O_7

By applying a highly sensitive homemade AC susceptibility technique to Pr_{x}Y_{1-x}Ba_2Cu_3O_7 polycrystals (with x=0.0, 0.1 and 0.3), we observed very sharp Fraunhofer type low-field periodic oscillations of the real part of the AC susceptibility which were attributed to Josephson vortices penetrating intergranular regions of grain-boundary Josephson network in our samples. Assuming the Lorentz type distribution of single-junction contact areas, we were able to successfully fit the experimental data.

cond-mat.supr-con↗

arXiv2008

Manifestation of vortex depinning transition in nonlinear current-voltage characteristics of polycrystalline superconductor Y_{1-x}Pr_{x}Ba_2Cu_3O_7

We present our recent results on the temperature dependence of current-voltage characteristics for polycrystalline Y_{1-x}Pr_{x}Ba_2Cu_3O_7 superconductors with x = 0.0, 0.1 and 0.3. The experimental results are found to be reasonably well fitted for all samples by a power like law. According to the theoretical interpretation of the obtained results, nonlinear deviation of our current-voltage characteristics curves from Ohmic behavior below Tc is attributed to the manifestation of dissipation processes related to the current induced depinning of Abrikosov vortices.

cond-mat.supr-con↗