Scientific Practical Materials Research Center of Belarus

Minsk, Belarus

Scientific Practical Materials Research Center of Belarus

Minsk, Belarus
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Kuzmin A.,University of Latvia | Efimov V.,Joint Institute for Nuclear Research | Efimova E.,Joint Institute for Nuclear Research | Sikolenko V.,Paul Scherrer Institute | And 2 more authors.
Solid State Ionics | Year: 2011

Temperature dependent (180-400 K) Co K-edge EXAFS spectra from perovskite-type rhombohedral (R3̄c) LaCoO3 have been successfully interpreted using a combination of classical NVT molecular dynamics (MD) and ab initio multiple-scattering (MS) theory. The method allowed us to account entirely for thermal disorder and to interpret reliably the contribution from the coordination shells beyond the first one into the total EXAFS spectrum taking into account many-body effects. The best agreement between experimental and configuration-averaged EXAFS spectra was obtained for pure ionic La 3+ and partially ionic Co1.35+ and O1.45- charges indicating the mixed ionic-covalent character of the Co - O bonds. © 2010 Elsevier B.V. All rights reserved.


Troyanchuk I.O.,Scientific Practical Materials Research Center of Belarus | Bushinsky M.V.,Scientific Practical Materials Research Center of Belarus | Sikolenko V.,Karlsruhe Institute of Technology | Efimov V.,Joint Institute for Nuclear Research | And 3 more authors.
European Physical Journal B | Year: 2013

The anion deficient cobaltite La0.5Ba0.5CoO 2.8 with the formal cobalt valence state close to 3+ has been studied as function of pressure up to 6.5 GPa at different temperatures by neutron powder diffraction. At ambient pressure the crystal structure of this compound has cubic symmetry (space group Pm-3m) and is found to become antiferromagnetic with TN close to 250 K. Applied pressure induces a gradual transition from the antiferromagnetic into a ferromagnetic state through a mixed magnetic state. The transition is not accompanied by obvious changes in the macroscopic crystal symmetry. It is suggested that the magnetic ground state strongly depends on the unit cell volume and that the transition is associated with a spin state crossover of the cobalt ions whereas the formal Co3+/Co4+ ratio is less important than expected following the double exchange scenario for the appearance of ferromagnetism.© EDP Sciences Società Italiana di Fisica Springer-Verlag 2013.


Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Kolasa A.,University Of Szczecin | Markevich S.A.,Scientific Practical Materials Research Center of Belarus
Physica Scripta | Year: 2012

We study the coherent dynamics of relaxing qubits driven by a bichromatic radiation in the dispersive regime in the case when the detuning of the frequency ω rf of a longitudinal radio-frequency field from the Rabi frequency ω 1 in a transverse microwave field is comparable in magnitude to ω rf and ω 1. We analytically describe this regime beyond the rotating wave approximation and find that the dominant feature of the dynamics of qubits is the shift in the Rabi frequency caused by the dynamical Zeeman and Bloch-Siegert-like effects. These fundamental effects can be experimentally separated because, unlike the Bloch-Siegert effect, the dynamical Zeeman effect depends on the detuning sign. Our theoretical results are in good agreement with the experimental data obtained in pulse electron paramagnetic resonance for the E′ 1 centers in crystalline quartz. © 2012 The Royal Swedish Academy of Sciences.


Troyanchuk I.O.,Scientific Practical Materials Research Center of Belarus | Bushinsky M.V.,Scientific Practical Materials Research Center of Belarus | Sikolenko V.,Helmholtz Center Berlin | Sikolenko V.,Joint Institute for Nuclear Research | And 5 more authors.
Journal of Alloys and Compounds | Year: 2014

Structural and magnetization measurements have been performed on the La0.7Sr0.3Mn0.85Nb0.15-x5+Mgx2+O3 stoichiometric compounds. With rise of the Mg2+ content the formal oxidation state manganese increases from +3 (x=0) up to +3.55 (x=0.15). The compositions with 0≤x≤0.08 undergo a structural transition from rhombohedral to orthorhombic symmetry below room temperature whereas x=0.1 and x=0.15 compounds are rhombohedral down to 2 K. The structural parameters evidence that the orthorhombic phase is not long-range orbitally ordered and that the structural transition is associated with a steric effect. The Mg-free compound is ferromagnetic with the Curie point of around 150 K and a magnetic moment of 3.1 bB/Mn. The substitution of Nb;b e with Mg;b e leads to a gradual weakening of the ferromagnetic component while in the x=0.15 compound A-type antiferromagnetic short-range order is stabilized in spite of macroscopic R3¯c symmetry. All the compositions show insulating behavior. It is suggested that ferromagnetism is originated from superexchange interactions via oxygen. Covalence enhances the positive part of the superexchange interactions whereas structural disorder induced by Nb;b e and Mg2+ions leads to suppression of ferromagnetism. © 2014 Elsevier B.V. All rights reserved.


Troyanchuk I.O.,Scientific Practical Materials Research Center of Belarus | Karpinsky D.,Scientific Practical Materials Research Center of Belarus | Efimov V.,Joint Institute for Nuclear Research | Sikolenko V.,Helmholtz Center Berlin | And 2 more authors.
Journal of Physics Condensed Matter | Year: 2014

La0.7Sr0.3Mn3+ 0.85Sb5+ 0.15O3 and La0.7Sr0.3Mn3+ 0.8Sb5+ 0.1Ge4+ 0.1O3 compounds with dominantly isovalent Mn3+ ions were studied by neutron powder diffraction and magnetization measurements. The compounds are basically ferromagnetic, with magnetic moments slightly above of 3 μB/Mn. Upon temperature decrease, the compounds exhibit structural transition from a rhombohedral phase to orbitally disordered orthorhombic one. The structural transitions occur well above the temperature of magnetic ordering (Tc ≈ 130 K). It is suggested that the ferromagnetic state is governed by the positive part of superexchange interactions Mn3+-O-Mn3+, which is enhanced by Mn(eg)-O(2p) hybridization. © 2014 IOP Publishing Ltd.


Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Markevich S.A.,Scientific Practical Materials Research Center of Belarus
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2014

The coherent dynamics of relaxing spin qubits driven by a classical bichromatic field comprising a strong resonant component and a weaker component with a frequency close to the strong-field Rabi frequency is studied. The double dressing by the bichromatic field modifies the dephasing and dissipation processes. We demonstrate that detuning of the weaker-field frequency from the strong-field Rabi frequency prolongs the decay of Rabi oscillations between some doubly dressed states. The sensitivity of Rabi oscillations to the modified detuning-dependent relaxation is illustrated for nitrogen-vacancy qubits in diamond. We discuss a steady-state population inversion of the doubly dressed-state levels. © 2014 IOP Publishing Ltd.


Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Markevich S.A.,Scientific Practical Materials Research Center of Belarus
Journal of Magnetic Resonance | Year: 2015

The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines. © 2015 Elsevier Inc. All rights reserved.


Saiko A.P.,Scientific Practical Materials Research Center of Belarus | Fedaruk R.,University Of Szczecin | Kolasa A.,University Of Szczecin
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2012

The geometric phase in the dynamics of a spin qubit driven by transverse microwave (MW) and longitudinal radio frequency (RF) fields is studied. The phase acquired by the qubit during the full period of the 'slow' RF field manifests in the shift of Rabi frequency 1 of a spin qubit in the MW field. We find out that, for a linearly polarized RF field, this shift does not vanish at the second and higher even orders in the adiabaticity parameter rf/1, where rf is the RF frequency. As a result, the adiabatic (Berry) phases for the rotating and counter-rotating RF components compensate each other, and only the higher order geometric phase is observed. We experimentally identify that phase in the frequency shift of the Rabi oscillations detected by a time-resolved electron paramagnetic resonance. © 2012 IOP Publishing Ltd.


PubMed | Scientific Practical Materials Research Center of Belarus, University Of Szczecin and Polish Academy of Sciences
Type: | Journal: Journal of magnetic resonance (San Diego, Calif. : 1997) | Year: 2016

Specific distortions of the EPR signal of bulk anthracite are observed at low temperatures. They are accompanied by variations in the microwave oscillator frequency and are explained by the manifestation of the Rabi splitting due to the strong coupling between electron spins and the cavity, combined with the use of an automatic frequency-control (AFC) system. EPR signals are recorded at negligible saturation in the temperature range of 4-300K with use of the AFC system to keep the oscillator frequency locked to the resonant frequency of the TM110 cylinder cavity loaded with the sample. For the sample with a mass of 3.6mg the line distortions are observed below 50K and increase with temperature lowering. The oscillator frequency variations are used to estimate the coupling strength as well as the number of spins in the sample. It is shown that the spin-cavity coupling strength is inversely proportional to temperature and can be used for the absolute determination of the number of spins in a sample. Our results indicate that at low temperatures even 10


PubMed | University Of Szczecin and Scientific Practical Materials Research Center of Belarus
Type: | Journal: Journal of magnetic resonance (San Diego, Calif. : 1997) | Year: 2015

The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines.

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