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110 results on '"Lashkul, A. V."'

1. Unusual scenario of the temperature evolution of magnetic state in novel carbon-based nanomaterials

Author

Ryzhov, V. A., Lashkul, A. V., Matveev, V. V., Mokeev, M. V., Molkanov, P. L., Kurbakov, A. I., Lisunov, K. G., Kiselev, I. A., Galimov, D., and Lahderanta, E.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Two porous carbon-based samples doped with Au and Co are investigated. The neutron diffraction study reveals an amorphous structure of both samples. The Co-doped sample exhibits a long-range ferromagnetic (FM) ordering at 2.6 K. The NMR investigations demonstrate, that the samples are obtained with a partial carbonization of initial aromatic compounds and do not reach a state of glassy carbon. The magnetization, longitudinal nonlinear response to a weak ac field and electron magnetic resonance data give evidences for presence of FM clusters in the samples well above 300 K. A short-range character of the FM ordering in the Au-doped sample transforms below T$_C \approx$ 210 K into another inhomogeneous FM state. Besides the FM clusters, this state contains a subsystem with a long-range FM ordering (matrix) formed by paramagnetic centers, existing outside the clusters. The nonlinear response data suggest a percolative character of the long-range FM matrix, which is connected probably with a porous sample structure. The magnetization data give evidence for the formation of an inhomogeneous state in the Co-doped sample, similar to that in the Au-doped one. However, this state is formed at higher temperatures, lying well above 350 K, and exhibits a more homogeneous arrangement of the FM nanoparticles and the FM matrix. Temperature dependence of the magnetization in the Au-doped sample is attributable to changes of the domain formation regime in the FM matrix on cooling, connected with the inhomogeneous character of its FM state. Such peculiarity is absent in the Co-doped sample below 350 K, which is in agreement with formation of the FM state in this sample at much higher temperatures. Further cooling below T ~ 3(10) K leads to a steep increase of the magnetization in both samples. This is attributable to the domain rearrangement in the inhomogeneous FM state at low temperatures., Comment: 32 pages with 12 figures

Published
2014

2. Structural and transport properties of GaAs/delta<Mn>/GaAs/InxGa1-xAs/GaAs quantum wells

Author

Aronzon, B. A., Kovalchuk, M. V., Pashaev, E. M., Chuev, M. A., Kvardakov, V. V., Subbotin, I. A., Rylkov, V. V., Pankov, M. A., Lagutin, A. S., Zvonkov, B. N., Danilov, Yu. A., Vihrova, O. V., Lashkul, A. V., and Laiho, R.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We report results of investigations of structural and transport properties of GaAs/Ga(1-x)In(x)As/GaAs quantum wells (QWs) having a 0.5-1.8 ML thick Mn layer, separated from the QW by a 3 nm thick spacer. The structure has hole mobility of about 2000 cm2/(V*s) being by several orders of magnitude higher than in known ferromagnetic two-dimensional structures. The analysis of the electro-physical properties of these systems is based on detailed study of their structure by means of high-resolution X-ray diffractometry and glancing-incidence reflection, which allow us to restore the depth profiles of structural characteristics of the QWs and thin Mn containing layers. These investigations show absence of Mn atoms inside the QWs. The quality of the structures was also characterized by photoluminescence spectra from the QWs. Transport properties reveal features inherent to ferromagnetic systems: a specific maximum in the temperature dependence of the resistance and the anomalous Hall effect (AHE) observed in samples with both "metallic" and activated types of conductivity up to ~100 K. AHE is most pronounced in the temperature range where the resistance maximum is observed, and decreases with decreasing temperature. The results are discussed in terms of interaction of 2D-holes and magnetic Mn ions in presence of large-scale potential fluctuations related to random distribution of Mn atoms. The AHE values are compared with calculations taking into account its "intrinsic" mechanism in ferromagnetic systems., Comment: 15 pages, 9 figures

Published
2007
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7. Influence of phase separation on the low-field magnetic properties of La1−xSrxMn1−yFeyO3

Author

Lisunov, Constantin, Laiho, Reino, Lashkul, Alexander V., Lähderanta, Erkki, Petrenko, Piotr, Nekrasova, Yu., and Zakhvalinskii, V.

Subjects
Physics, QC1-999, Electronics, TK7800-8360
Abstract

The magnetic properties of ceramic La1−xSrxMn1−yFeyO3 samples with x = 0.3 and y = 0.15−0.25 are investigated in magnetic fields of B = 10−103 G at a temperature T between 5−310 K. A ferromagnetic transition at TC, decreasing considerably with y, is accompanied with strong magnetic irreversibility at B = 10 G. The critical behavior of χ (T) ~ (T/TC − 1)−γ is governed at y = 0.15−0.20 by the percolative (γ ≈ 1.8) and Heisenberg (γ ≈ 1.4) spin systems.

Published
2010

8. Magnetic and galvanomagnetic properties of CdSb doped with Ni

Author

Lähderanta, Erkki, Laiho, Reino, Lashkul, Alexander V., Lisunov, Constantin, Shakhov, Mihail, and Zakhvalinskii, V.

Subjects
Physics, QC1-999, Electronics, TK7800-8360
Abstract

Magnetic and galvanomagnetic properties of the group II-V semiconductor CdSb single crystals doped with Ni are reported. The magnetization data give evidence for spheroidal Ni- rich Ni1-xSbx nanoclusters. Mechanism of the low-temperature conductivity is sensitive to the magnetic field, being of the variable-range hopping type in zero field and of the nearest- neighbor hopping type in strong fields. The Hall resistivity contains the normal and the anomalous contributions.

Published
2009

23. Structural and magnetic properties of In1-xMnxSb: Effect of Mn complexes and MnSb nanoprecipitates.

Author

Kochura, A. V., Aronzon, B. A., Lisunov, K. G., Lashkul, A. V., Sidorenko, A. A., De Renzi, R., Marenkin, S. F., Alam, M., Kuzmenko, A. P., and Lähderanta, E.

Subjects
MAGNETIC properties, MAGNETIC semiconductors, NUCLEAR magnetic resonance, INDIUM antimonide crystals, MANGANESE, ANTIMONY, X-ray diffraction, MICROCRYSTALLINE polymers
Abstract

Structural and magnetic properties of the group III-V diluted magnetic semiconductor In1-xMnxSb with x = 0.005-0.06, including the nuclear magnetic resonance (NMR) investigations, are reported. Polycrystalline In1-xMnxSb samples were prepared by direct alloying of indium antimonide, manganese and antimony, followed by a fast cooling of the melt with a rate of 10-12 K/s. According to the X-ray diffraction data, part of Mn is substituted for In, forming the In1-xMnxSb matrix. Atomic force microscopy and scanning tunneling microscopy investigations provide evidence for the presence of microcrystalline MnSb inclusions (precipitates), having a size of ∼100-600 nm, and the fine structure of nanosize grains with a Gaussian distribution around the diameter of ∼24 nm. According to the NMR spectra, the majority of Mn enters the MnSb inclusions. In addition to the single Mn ions, which contribute to the magnetization M (T) only in the low-temperature limit of T < 10-20 K, and MnSb nanoprecipitates responsible for the ferromagnetic (FM) properties of In1-xMnxSb, a superparamagnetic (SP) contribution of atomic-size magnetic Mn complexes (presumably dimers) has been established. The fraction of the MnSb phase, η ∼ 1-4%, as well as the concentration, nsp ∼ (0.8-3.2) × 1019 cm-3, and the magnetic moment of the Mn dimers, μ ∼ 8-9 μB, are determined. The solubility limit of Mn in the InSb matrix, NSL ∼ 1020 cm-3, is estimated. Hysteresis in low (H < 500 Oe) magnetic fields and saturation of the magnetization in high (H > 20 kOe) magnetic fields are observed, indicating a presence of the SP and FM contributions to the dependence of M (H) up to T ∼ 500 K. The hysteresis is characterized by the coercivity field, Hc, decreasing between ∼100 and 75 Oe when T is increased from 5 to 510 K. The values of Hc are in reasonable agreement with the effect of the largest MnSb inclusions. The maximum of M (T), measured in the zero-field-cooled and the field-cooled conditions in a weak field of 500 Oe, is observed at T ∼ 510 K and is attributable to the Hopkinson effect. [ABSTRACT FROM AUTHOR]

Published
2013
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24. Ferromagnetism of low-dimensional Mn-doped III-V semiconductor structures in the vicinity of the insulator-metal transition.

Author

Aronzon, B. A., Pankov, M. A., Rylkov, V. V., Meilikhov, E. Z., Lagutin, A. S., Pashaev, E. M., Chuev, M. A., Kvardakov, V. V., Likhachev, I. A., Vihrova, O. V., Lashkul, A. V., Lähderanta, E., Vedeneev, A. S., and Kervalishvili, P.

Subjects
FERROMAGNETISM, HOLES (Electron deficiencies), MANGANESE, SEMICONDUCTOR doping, METAL-insulator transitions, HALL effect, MAGNETORESISTANCE
Abstract

The structural and transport properties of GaAs/Mn/GaAs/InxGa1-xAs/GaAs quantum wells (x≈0.2) with Mn δ-layer (4–10 at. %), separated from the well by a GaAs spacer, have been studied. The hole mobility in the investigated structures has exceeded the values known for magnetic III-V heterostructures by two orders of magnitude. For structures with the conductivity of the metal type, we have succeeded to observe at low temperatures Shubnikov–de Haas oscillations just confirming the two dimensionality (2D) of the hole energy spectrum. Exactly those 2D holes promote the ferromagnetic ordering of the Mn layer. That has been proven by (i) observing maxima (at 25–40 K) in temperature dependencies of the resistance, which positions agree with calculated values of Curie temperatures (for structures with the indirect interaction of Mn atoms via 2D holes), and (ii) revealing the negative spin-dependent magnetoresistance (NMR) as well as the anomalous Hall effect (AHE), which values are also in good agreement with calculations relating to ferromagnetic 2D III-V systems. As for the structures with the insulator type of the conductivity, their NMR and AHE features evidence the phase separation—the sample fragmentation with the formation of mesoscopic ferromagnetic areas separated by paramagnetic strata of the high tunnel conductivity. [ABSTRACT FROM AUTHOR]

Published
2010
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29. Photoluminescence of Flux Grown GaN Crystals

Author

Zherebtsov, D. A., primary, Sirkeli, V. P., additional, Disalvo, F. J., additional, Lahderanta, E., additional, Xu, K., additional, Lashkul, A. V., additional, Laiho, R., additional, Bobylev, A. Yu., additional, Liu, Z. L., additional, Vinnik, D. A., additional, Galimov, D. M., additional, Dyachuk, V. V., additional, and Zakharov, V. G., additional

Published
2013
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33. MAGNETIC AND MAGNETO-OPTICAL PROPERTIES OF Ti1-xVxO2-δ SEMICONDUCTOR OXIDE FILMS: ROOM TEMPERATURE FERROMAGNETISM VERSUS RESISTIVITY

Author

ORLOV, A. F., primary, BALAGUROV, L. A., additional, KULEMANOV, I. V., additional, PETROVA, E. A., additional, PEROV, N. S., additional, GAN'SHINA, E. A., additional, FETISOV, L. YU., additional, SEMISALOVA, A. S., additional, NOVIKOV, A. I., additional, YASHINA, L. V., additional, ROGALEV, A., additional, SMEKHOVA, A., additional, LASHKUL, A. V., additional, and LÄHDERANTA, E., additional

Published
2012
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37. Magnetic Properties of ZnSe Crystals doped with Transition Metals

Author

Laiho, Reino, primary, Lashkul, Alexander V., additional, Lähderanta, Erkki M., additional, Nedeoglo, Dmitrii D., additional, Nedeoglo, Natalia D., additional, Radevici, Ivan V., additional, Sirkeli, Vadim P., additional, Sushkevich, Konstantin D., additional, Ferro, Gabriel, additional, and Siffert, Paul, additional

Published
2010
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43. Structural and transport properties of GaAs/δ-Mn/GaAs/InxGa1−xAs/GaAs quantum wells

Author

Aronzon, B A, primary, Kovalchuk, M V, additional, Pashaev, E M, additional, Chuev, M A, additional, Kvardakov, V V, additional, Subbotin, I A, additional, Rylkov, V V, additional, Pankov, M A, additional, Likhachev, I A, additional, Zvonkov, B N, additional, Danilov, Yu A, additional, Vihrova, O V, additional, Lashkul, A V, additional, and Laiho, R, additional

Published
2008
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48. Irreversible magnetic properties of carbon nanoparticles.

Author

Lahderanta, E., Lashkul, A. V., Lisunov, K. G., Zherebtsov, D. A., Galimov, D. M., and Titkov, A. N.

Subjects
*CARBON, *NANOPARTICLES, *MAGNETIC fields, *HYSTERESIS, *MAGNETISM
Abstract

Magnetic properties of powder and glassy samples with carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co, are investigated at temperatures T ~ 3 - 300 K in magnetic fields B up to 5 T. Magnetization M (7) exhibits in low fields of B = 1 - 50 mT a strong irreversibility, which is suppressed above B ~ 1 T. The high-temperature (T ~ 200 - 300 K) dependence of M on B demonstrates a saturation above B ~ 2 T. Magnetic hysteresis is observed already at 300 K, exhibiting a power-law temperature decay of the coercive field. Analysis of the experimental data suggests a concentration of the magnetization close to the surface of the carbon nanoparticles. This is consistent with the origin of magnetism in nanocarbon due to intrinsic surface defects. Deviations of macroscopic and microscopic parameters in the Co-doped sample from those in the other samples imply an influence of the Co ions and/or clusters. [ABSTRACT FROM AUTHOR]

Published
2013
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49. Magnetic Properties of ZnSe Crystals doped with Transition Metals.

Author

Laiho, Reino, Lashkul, Alexander V., Lähderanta, Erkki M., Nedeoglo, Dmitrii D., Nedeoglo, Natalia D., Radevici, Ivan V., Sirkeli, Vadim P., and Sushkevich, Konstantin D.

Subjects
*MAGNETIC crystals, *ZINC selenide, *TRANSITION metals, *ANTIFERROMAGNETISM, *PHASE equilibrium, *SEMICONDUCTOR doping, *CRYSTAL growth, *ANNEALING of crystals
Abstract

The magnetic properties of ZnSe:Fe, ZnSe:Mn and ZnSe:Cr crystals are investigated. It is established that magnetic properties of ZnSe:Fe differ from magnetic properties of ZnSe doped with other transition metals, for example Cr2+ or Mn2+, because of Fe2+ ions ground state has a permanent magnetic moment. For ZnSe crystals doped from Zn+Fe the two subsystems are observed: paramagnetic and anti-ferromagnetic with TC = -130 K (B = 67 G). It is shown that ZnSe:Fe magnetic properties are sensible to the crystals doping technique. We proposed a model, that explains formation of the few magnetic phases (paramagnetic, antiferromagnetic and 'spin-glass' phase) in ZnSe:Fe as result of nonuniform doping and formation of the impurity clusters in crystal. It is shown that the most uniform crystal doping may be obtained in case of doping during the growth process or at thermal annealing in Bi melt. [ABSTRACT FROM AUTHOR]

Published
2010
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