Publications on the project |
005 Unconventional ferromagnetism and transport properties of (In,Mn)Sb dilute magnetic semiconductor |
Authors: | V. N. Krivoruchko, V. Yu. Tarenkov, D. V. Varyukhin, A. I. D'yachenko, O. N. Pashkova, V. A. Ivanov | |
Summary: | Narrow-gap higher mobility semiconducting alloys In1−xMnxSb were synthesized in polycrystalline form and their magnetic and transport properties have been investigated. Ferromagnetic order in In0.98Mn0.02Sb was unambiguously established by the observation of clear hysteresis loops up to room temperature in direct magnetization measurements. An unconventional (reentrant) magnetization versus temperature behavior has been found. The observed peculiarities we explained within the frameworks of recent models which suggest that a strong temperature dependence of the carrier density is a crucial parameter determining carrier-mediated ferromagnetism of III-Mn-V semiconductors. The correlation between the magnetic state and transport properties of the sample has been investigated. Direct measurements of the degree of charge current spin polarization have been carried out using the point contact Andreev reflection (AR) spectroscopy. The AR data are analyzed by introducing a quasiparticle spectrum broadening, which is likely to be related to inelastic scattering in the contact. The AR spectroscopy data argued that at low temperature the sample is decomposed on metallic ferromagnetic clusters with relatively high spin polarization of charge carriers (up to 65% at 4.2K) within a cluster. | |
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Edition: | J.Magn.Magn.Mater. | | | 2010,
915-923,English |
005 Reflection of strong electronic correlations in tunnel spectra of contacts with manganites |
Authors: | A. I. D'yachenko, V.A. Boichenko, V. Yu. Tarenkov | |
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Edition: | | | | 2010,
,Russian |
005 005 Tunnel density of states of a ferromagnetic and superconductor contact |
Authors: | I.V. Boilo, A.V. Golovchan, V.E. Shaternik | |
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Edition: | | | | 2010,
,Russian |
005 Triple-gap superconductivity of MgB2-(La,Sr)MnO3 composite |
Authors: | V. N. Krivoruchko, V. Yu. Tarenkov | |
Summary: | The interplay of superconductivity and magnetism was studied in a composite prepared from ferromagnetic half-metallic La0.67Sr0.33MnO3 (LSMO) nanoparticles and the s-wave superconductor MgB2. A few principal effects have been found. With the onset of MgB2 superconductivity, a spectacular drop of the sample resistance was detected and complete superconductivity was observed at temperatures up to 20 K. The basic nanocomposite characteristics (critical temperature, current-voltage dependence, percolation threshold, etc.) are strongly affected by the half-metallic LSMO and, most probably, cannot be quantitatively explained within the framework of a conventional percolation scenario. Point contact (PC) spectroscopy was used to measure directly the superconducting energy coupling. For small voltage, an excess current and doubling of the PC normal-state conductance were detected. Conductance peaks corresponding to three energy gaps are clearly observed. Two of these gaps we identified as enhanced Δπ and Δσ gaps originating from the MgB2; the third gap Δtr is more than three times larger than the largest MgB2 gap. The temperature behavior of Δtr does not followtheBCSdependence. The experimental results have a natural and qualitative explanation within the phase-coherency scenario of proximity-induced superconductivity. Specifically, at low temperature, a p-wave spin-triplet condensate with pairing energy Δtr is essentially sustained in LSMO but is incapable of displaying a long-range superconducting response because of a phase-disordered state. The proximity coupling to MgB2 restores the long-range phase coherency of the superconducting state, which, in turn, enhances the superconducting state of the MgB2. | |
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Edition: | Phys. Rev. B | | | 2012,
104502 (1-11),English |
005 Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article) |
Authors: | V.N. Krivoruchko, А.I. Dyachenko, V.Y. Tarenkov | |
Summary: | Materials with spin-polarized charge carriers are the most demanded in the spin-electronics. Particularly requested are the so-called half-metals, which have the maximum attainable value of carrier spin polarization. Doped manganites are in the list of compounds with, potentially, half-metallic properties. The point-contact (PC) Andreev reflection (AR) spectroscopy is a robust and direct method to measure the degree of current spin polarization. In this report, advances in PCAR spectroscopy of ferromagnetic manganites are reviewed. The experimental results obtained on “classic” s-wave superconductor — ferromagnetic manganites PCs, as well as related theoretical models applied to deduce the actual value of charge carrier spin-polarization, are discussed. Data obtained on “proximity affected” contacts is also outlined. Systematic and repeatable nature of a number of principal experimental facts detected in the AR spectrum of proximity affected contacts suggests that some new physical phenomena have been documented here. Different models of current flow through a superconductor–half-metal ferromagnet interface, as well as possibility of unconventional superconducting proximity effect, have been discussed. | |
Keywords: | current spin polarization, Andreev-reflection spectroscopy, ferromagnetic manganites, unconventional | |
Edition: | Low Temp. Phys. | | | 2013,
276 – 292,English |
005 The transport characteristics of a superconductor–ferromagnet composite |
Authors: | V.V. Kononenko, V.Yu. Tarenkov, A.I. D’yachenko, V.N. Varyuhin | |
Summary: | The transport characteristics of a composite that consists of superconductor MgB2 and nanopowder manganite La0.7Sr0.3MnO3 (LSMO) are investigated. It is found that when the ferromagnet content is more than ten percent by volume increases sharply the composite resistivity. This is caused by a breach of percolation paths for microparticles of magnesium diboride, resulting in the formation of a grid of the superconductor–ferromagnet–superconductor contacts and a significant broadening of the superconducting transition of the composite compared to a pure MgB2 sample. The data obtained show that the passage of the Cooper pairs through a ferromagnet half metal (thickness d > 10 nm) with a high (about 100%) spin polarization of the carriers is quite possible. | |
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Edition: | Low Temp. Phys. | | | 2014,
274-279,Russian |
005 Andreev-spectroscopy study of unconventional superconductivity in MgB2:(La,Sr)MnO3 nanocomposite |
Authors: | V.N. Krivoruchko, A.I. D’yachenko, V.Yu. Tarenkov | |
Summary: | Unconventional high-temperature superconductivity in MgB2:La0:65Sr0:35MnO3 (MgB:LSMO) nanocomposite has been found recently [Phys. Rev. B 86, 10502 (2012)]. In this report, the symmetry of the nanocomposite superconducting order parameter and plausible pairing mechanisms have been studied by the point-contact Andreev-reflection (PCAR) spectroscopy. To clarify the experimental results obtained, we consider a model of a ferromagnetic superconductor, which assumes a coexistence of itinerant ferromagnetism and mixed-parity superconductivity. The Balian–Werthamer state, with quasiparticle gap topology of the same form as that of the ordinary s-wave state, fits the experimental data reasonably well. Utilizing the extended Eliashberg formalizm, we calculated the contribution of MgB2 in the total composite’s conductivity and estimated the magnitude of the electron–phonon effects originated from MgB2 in I–V characteristics of the composite at above-gap energies. It was found that distinctive features observed in the PC spectra of the MgB:LSMO samples and conventionally attributed to the electron–phonon interaction cannot be related to the MgB2 phonons. It is argued that the detected singularities may be a manifestation of the electron-spectrum renormalizations due to strong magnetoelastic (magnon–phonon) interaction in LSMO. | |
Keywords: | unconventional superconductivity, heterostructures, Andreev reflection | |
Edition: | Low Temp. Phys. | | | 2014,
,English |
The events in the framework of the project |
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005 Krivoruchko Vladimir N.Professor, Doctor of sciences (physics & mathematics) Deputy Director for Science +38062342-9962
005 1.1. Nanophysics: fundamental problems Purpose: Expected results:Issue of new types of products: methods, theories Stage 1:Аномальні властивості наноструктур феромагнітний манганіт – низькотемпературний надпровідник Stage 2:Магнітні та транспортні властивості розбавлених магнітних напівпровідників. Stage 3:Ефекти спінової інжекції у близькісних та джозесонівських гетероструктурах Stage 4:Аномальні магнітні та транспортні властивості наноструктурованих магнітних напівпровідник та напівметалів Stage 5:Ефекти близькості в джозесонівських структурах на базі магнітних напівпровідників та напівметалів
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