arXiv subjects

A. A. Pronin

Publications and source records attributed to A. A. Pronin.

17 recordsLinked to original sources

arXiv2023

Phenomenological model of supercooled liquid as a possible resolution of the Kauzmann paradox

The diverging relaxation time in approaching hypothetical ideal glass transition is a subject of hot debate. In the current paper we demonstrate, how diverging relaxation time and turning excess entropy to zero (which is an essence of Kauzmann's paradox) can be avoided, using as an example the model molecular glassformer, propylene carbonate. For this purpose we compare its thermodynamic and dielectric relaxation properties, both known from the literature. The agreement between two sets of data can be achieved, if we suppose, that enthalpy of supercooled liquid propylene carbonate is governed by activation law, and relaxation time follows double exponential law. We propose the generalized Adam-Gibbs law to reconcile this two dependencies, and qualitatively discuss its implications.

cond-mat.soft↗

arXiv2021

Dielectric constant of disordered phases of the smallest monoalcohols : evidence for the hindered plastic crystal phase

With gradual temperature increase in premelting regions of solid phase of methanol and high pressure phase of ethanol, and using novel procedure of separation of electrode polarization effects, we are able to register the contribution of relaxation process to low-frequency dielectric constant. This contribution is about half the liquid's dielectric constant near temperature of solidification , and is almost an order of magnitude higher than reported earlier for ambient pressure phase of methanol. As opposed to dielectric constant of water at ambient pressure, which does not change much during crystallization, our finding indicates the hindrance of molecule rotation in orientationally disordered phases of monoalcohols. Similar dielectric responses of ambient pressure methanol and high-pressure phase of ethanol imply existence of hindered plastic crystal phase of ethanol (not observed at low pressures). We also have found some dynamic disorder in nominally fully ordered phase of these monoalcohols ($α$-phase of methanol and low-pressure phase of ethanol), the contribution of this disorder being dependent on external conditions (e.g. temperature), and increasing at approaching the order-disorder transition. On the other hand, the amplitude of dielectric responce in hindered plastic crystal phases is almost independent of temperature.

cond-mat.mtrl-sci↗

arXiv2014

Spin-polarized electron transport in the high-pressure ferromagnetic phases (GaSb)$_2$M (M=Cr,Mn)

For the first time magnetrotransport of the ferromagnetic high-pressure phases of (GaSb)$_2$M (M=Cr,Mn) was measured. It was found that the main component of magnetotransport in these phases is negative and its amplitude is increasing with temperature rising and approaching Curie temperature. Measuring of magnetoresistance in the cycling magnetic fields demonstrated that the Yosida component of magnetresistance is negligible and the main part of the magnetoresistance can be attributed to the spin-polarized electron transport.

cond-mat.mtrl-sci↗

arXiv2013

Phase transformations in methanol at high pressure measured by dielectric spectroscopy technique

Dielectric response in methanol measured in wide pressure and temperature range ($P < 6.0$ GPa; 100 K $ $ 1.2 GPa $T < 270$ K. In the intermediate P-T region $P \approx 3.4-3.7$ GPa $T \approx 260-280$ K a set of complicated structural transformations occurs involving four methanol crystalline structures. At higher pressures within a narrow range $P \approx 4.3-4.5$ GPa methanol can be obtained in the form of fragile glass ($T_g \approx 200$ K, $m_p \approx 80$ at $P= 4.5$ GPa) by relatively slow cooling.

cond-mat.mtrl-sci↗

arXiv2013

Dielectric Spectroscopy and Ultrasonic Study of Propylene Carbonate under Ultra-high Pressures

We present the high pressure dielectric spectroscopy (up to 4.2 GPa) and ultrasonic study (up to 1.7 GPa) of liquid and glassy propylene carbonate (PC). Both of the methods provide complementary pictures of the glass transition in PC under pressure. No other relaxation processes except $α$-relaxation have been found in the studied pressure interval. The propylene carbonate liquid is a glassformer where simple relaxation and the absence of $β$-relaxation are registered in the record-breaking ranges of pressures and densities. The equation of state of liquid PC was extended up to 1 GPa from ultrasonic measurements of bulk modulus and is in good accordance with the previous equations developed from volumetric data. We measured the bulk and shear moduli and Poisson's ratio of glassy PC up to 1.7 GPa. Many relaxation and elastic properties of PC can be qualitatively described by the soft-sphere or Lennard-Jones model. However, for the quantitative description of entire set of the experimental data, these models are insufficient. Moreover, the Poisson coefficient value for glassy PC indicates a significant contribution of non-central forces to the intermolecular potential. The well-known correlation between Poisson's ratio and fragility index (obtained from dielectric relaxation) is confirmed for PC at ambient pressure, but it is violated with pressure increase. This indicates that different features of the potential energy landscape are responsible for the evolution of dielectric response and elasticity with pressure increase.

cond-mat.soft↗

arXiv2011

Observation of non-local dielectric relaxation in glycerol

Since its introduction, liquid viscosity and relaxation time $τ$ have been considered to be an intrinsic property of the system that is essentially local in nature and therefore independent of system size. We perform dielectric relaxation experiments in glycerol, and find that this is the case at high temperature only. At low temperature, $τ$ increases with system size and becomes non-local. We discuss the origin of this effect in a picture based on liquid elasticity length, the length over which local relaxation events in a liquid interact via induced elastic waves, and find good agreement between experiment and theory.

cond-mat.soft↗

arXiv2011

Spin excitations of the correlated semiconductor FeSi probed by THz radiation

By direct measurements of the complex optical conductivity $σ(ν)$ of FeSi we have discovered a broad absorption peak centered at frequency $ν_{0}(4.2 K) \approx 32 cm^{-1}$ that develops at temperatures below 20 K. This feature is caused by spin-polaronic states formed in the middle of the gap in the electronic density of states. We observe the spin excitations between the electronic levels split by the exchange field of $H_{e}=34\pm 6 T$. Spin fluctuations are identified as the main factor determining the formation of the spin polarons and the rich magnetic phase diagram of FeSi.

cond-mat.str-el↗

arXiv2011

Electrotransport and magnetic properies of Cr-GaSb spintronic materials synthesized under high pressure

Electrotarnsport and magnetic properties of new phases in the system Cr-GaSb were studied. The samples were prepared by high-pressure (P=6-8 GPa) high-temperature treatment and identified by x-ray diffraction and scanning electron microscopy (SEM). One of the CrGa$_2$Sb$_2$ phases with an orthorhombic structure $Iba2$ has a combination of ferromagnetic and semiconductor properties and is potentially promising for spintronic applications. Another high-temperature phase is paramagnetic and identified as tetragonal $I4/mcm$.

cond-mat.mtrl-sci↗

arXiv2010

Glassy Dynamics Under Superhigh Pressure

Nearly all glass-forming liquids feature, along with the structural alpha-relaxation process, a faster secondary process (beta-relaxation), whose nature belongs to the great mysteries of glass physics. However, for some of these liquids, no well-pronounced secondary relaxation is observed. A prominent example is the archetypical glass-forming liquid glycerol. In the present work, by performing dielectric spectroscopy under superhigh pressures up to 6 GPa, we show that in glycerol a significant secondary relaxation peak appears in the dielectric loss at P > 3 GPa. We identify this beta-relaxation to be of Johari-Goldstein type and discuss its relation to the excess wing. We provide evidence for a smooth but significant increase of glass-transition temperature and fragility on increasing pressure.

cond-mat.dis-nn↗

arXiv2005

Quantum critical behavior induced by Mn impurity in CuGeO3

Results of high frequency (60-315 GHz) studies of ESR in CuGeO3 single crystals containing 0.9% of Mn impurity are reported. Quantitative EPR line shape analysis allowed concluding that low temperature magnetic susceptibility for T <40 K diverges following power law with the critical exponent 0.81 and therefore manifests onset of a quantum critical (QC) regime. We argue that transition into Griffiths phase occurs at TG~40 K and disorder produced by Mn impurity in quantum spin chains of CuGeO3 may lead to co-existence of the QC regime and spin-Peierls dimerisation.

cond-mat.str-el↗

arXiv2004

The Competition between Staggered Field and Antiferromagnetic Interactions in Cugeo3:Fe

The EPR spectra along different crystallographic axes for single crystals of CuGeO3 containing 1% of Fe impurity have been studied in the frequency range 60-360 GHz at temperatures 0.5-30 K. The analysis based on the Oshikawa-Affleck (OA) theory suggests that the temperature dependences of the line width and g-factor are formed as a result of the competition between interchain antiferromagnetic interactions and staggered Zeeman energy. It is found that staggered magnetic moments in CuGeO3:Fe are located predominantly along b axis.

cond-mat.str-el↗

arXiv2004

Quantum Critiality and Collective Effects in Low Dimensional Magnet CuGeO3 Probed by High Frequency EPR

For the CuGeO3 single crystals doped with 1% of Fe the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: a=0.34 (B //a and B //c) and a=0.31 (B //b). The description of the temperature dependences of the line width and g-factor could be obtained in the OA theory assuming that staggered component of the magnetic moment is located predominantly along b axis. Possible arguments favoring the competition between effects of the staggered field and antiferromagnetic ordering are provided.

cond-mat.str-el↗

arXiv2004

Disorder driven quantum critical behavior in CuGeO3 doped with magnetic impurity

For the CuGeO3 doped with 1% of Fe the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: a=0.34 (B//a and B//c) and a=0.31 (B//b). New effect of the frequency dependence of the critical exponent is discussed.

cond-mat.str-el↗

arXiv2004

High Frequency EPR Spectroscopy of Germanium Cuprate. I. The Case of Doping with Cobalt

Resonant magnetoabsorption spectra for CuGeO3 single crystals containing 2% of Co impurity are studied in the frequency range 60-360 GHz in magnetic field up to 16 T at temperatures 2-60 K. It is found that together with the resonance on Cu2+ chains a new absorption line related with Co2+ ions appears in EPR spectrum. The full set of spectroscopic data (g-factors, linewidths, integrated intensities) have been determined for both resonances. The obtained results exhibit considerable deviations from the universal scenario of doping for CuGeO3 and discussed in the frames of the models of the quantum critical behavior and the three-dimensional antiferromagnet with the reduced by disorder Neel temperature. The Oshikawa and Affleck theory for EPR in 1D S=1/2 AF spin chain is compared with experiment.

cond-mat.str-el↗

arXiv2003

Quantum critical point in CuGeO3 doped with magnetic impurities

Using high frequency (up to 450 GHz) ESR and low temperature specific heat measurements we find that insertion of 1% Fe and 2% Co damps spin-Peierls and Neel transitions and for T<30K gives rise to onset of a quantum critical behaviour characteristic for a random dimer Griffiths phase.

cond-mat.str-el↗

arXiv2001

Decay of spin-Peierls state in CuGeO3:Fe. The case of a strong disorder

Influence of doping by iron impurity on spin-Peierls state in CuGeO3 is studied. ESR measurements for the frequency/temperature domain 60-450 GHz/ 1.8-300 K and specific heat data obtained for the interval 6-20 K show that insertion of 1% of Fe completely destroy both spin-Peierls and antiferromagnetic orders. Damping of long-range magnetic order is accompanied by onset at T<20 K of power asymptotics for magnetic susceptibility chi~T^-alpha and magnetic part of specific heat cm~T^(1-alpha), with the index alpha=0.35-0.37. This effect is characteristic to the limit of strong disorder for doped CuGeO3 and may reflect formation of the Griffiths phase at low temperatures in CuGeO3:Fe.

cond-mat.str-el↗

arXiv1999

Critical behavior in NaV2O5: the case of dielectric function and the aspect of universality

Temperature dependence in the interval 4.2-300 K and the critical behavior of the dielectric function along c-axis in NaV2O5 have been studied in the frequency range 1 MHz-1 GHz. These data were analyzed together with literature data concerning specific heat, magnetic losses and ultrasonic velocity. We found that all results support the idea about universality of the critical laws at the transition in NaV2O5 where different physical quantities demonstrate identical shape of the anomaly. Considerable deviations from the standard theory of the second order transition including asymmetry of the critical behavior above and below transition and appearance of the anomalous background are detected.

cond-mat.str-el↗