A. P. Gerashchenko
Russian Academy of Sciences
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Featured researches published by A. P. Gerashchenko.
Journal of Experimental and Theoretical Physics | 2012
A. F. Sadykov; A. P. Gerashchenko; Yu. V. Piskunov; V. V. Ogloblichev; A. G. Smol’nikov; S. V. Verkhovskii; A. Yu. Yakubovskii; E. A. Tishchenko; A. A. Bush
The complex NMR study of the magnetic structure of LiCu2O2 multiferroic has been performed. It has been shown that the spin spirals in LiCu2O2 are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu2+ chains. A magnetic field of H0 = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H0 ‖ b.
Jetp Letters | 2000
K. N. Mikhalev; S. A. Lekomtsev; A. P. Gerashchenko; V. E. Arkhipov; A. V. Korolev; Ya. M. Mukovskii; A. A. Arsenov
Magnetic susceptibility of the La0.9MnO3 single crystal was measured and its (139La, 55Mn) NMR spectra were recorded. The data obtained indicate that the areas with an A-type antiferromagnetic order (TN=140 K) and magnetic moments aligned with the b axis occupy a major part of the sample volume in manganite with a considerable concentration of cationic vacancies; simultaneously, the clusters with a canted magnetic sublattice and ferromagnetic interaction between magnetic moments are formed near the vacancies. Charge distribution in these clusters is materially different from that in the antiferromagnetic areas. Magnetic state and relative concentration of the clusters are discussed.
Journal of Experimental and Theoretical Physics | 2014
A. F. Sadykov; A. P. Gerashchenko; Yu. V. Piskunov; V. V. Ogloblichev; A. G. Smol’nikov; S. V. Verkhovskii; A. L. Buzlukov; I. Yu. Arapova; Y. Furukawa; A. Yu. Yakubovskii; A. A. Bush
The magnetic structure of a quasi-one-dimensional frustrated NaCu2O2 magnet single crystal is studied by NMR. The spatial orientation of the planar spin spirals in the copper-oxygen Cu2+-O chains is determined, and its evolution as a function of the applied magnetic field direction is analyzed.
Jetp Letters | 2015
A. G. Smol’nikov; V. V. Ogloblichev; S. V. Verkhovskii; K. N. Mikhalev; A.Yu. Yakubovskii; K. Kumagai; Y. Furukawa; A. F. Sadykov; Yu. V. Piskunov; A. P. Gerashchenko; S. N. Barilo; S. V. Shiryaev
The magnetically ordered phase of the CuCrO2 single crystal has been studied by the nuclear magnetic resonance (NMR) method on 53Cr nuclei in the absence of an external magnetic field. The 53Cr NMR spectrum is observed in the frequency range νres = 61–66 MHz. The shape of the spectrum depends on the delay tdel between pulses in the pulse sequence τπ/2–tdel–τπ–tdel–echo. The spin–spin and spin–lattice relaxation times have been measured. Components of the electric field gradient, hyperfine fields, and the magnetic moment on chromium atoms have been estimated.
Jetp Letters | 2010
A. F. Sadykov; A. P. Gerashchenko; Yu. V. Piskunov; V. V. Ogloblichev; A. L. Buzlukov; S. V. Verkhovskii; A. Yu. Yakubovskii; K. Kumagai
The NMR spectra of 63Cu and 65Cu natural copper isotopes in a LiCu2O2 multiferroic single crystal compound have been measured above and below the temperature of magnetic phase transition (Tc = 23 K) in zero magnetic field and in applied magnetic field H0 = 94 kOe parallel to the c axis of the crystal. In LiCu2O2 below Tc, a complicated helical magnetic structure with the magnetic moment of copper ions Cu2+ varying along the chain according to the harmonic law with the wave vector being incommensurate to the crystal lattice constants has been revealed. The experimental results have been successfully interpreted using the model based on the planar helical magnetic structure. It has been found that the plane of rotation for Cu2+ magnetic moments in LiCu2O2 does not coincide at H0 = 0 with the ab plane. The high magnetic field (H0 = 94 kOe) applied along the c axis of the single crystal does not affect the spatial orientation of the plane of rotation.
Journal of Experimental and Theoretical Physics | 2017
A. F. Sadykov; Yu. V. Piskunov; A. P. Gerashchenko; V. V. Ogloblichev; A. G. Smol’nikov; S. V. Verkhovskii; I. Yu. Arapova; Z. N. Volkova; K. N. Mikhalev; A. A. Bush
A comprehensive NMR study of the magnetic properties of single crystal LiCu2O2 (LCO) and NaCu2O2 (NCO) is carried out in the paramagnetic region of the compounds for various orientations of single crystals in an external magnetic field. The values of the electric-field gradient (EFG) tensor, as well as the dipole and transferred hyperfine magnetic fields for 63,65Cu, 7Li, and 23Na nuclei are determined. The results are compared with the data obtained in previous NMR studies of the magnetically ordered state of LCO/NCO cuprates.
Jetp Letters | 1998
A. V. Anan’ev; Yu.I. Zhdanov; A. P. Gerashchenko; K. N. Mikhalev; S. V. Verkhovskii; E. Yu. Medvedev; K. Okulova; N. I. Chebotaev; V. N. Goshchitskii
The spin-spin relaxation rate 63T2−1 of 63Cu nuclei in CuO2 layers is measured in the normal and superconducting states of the compound YBa2Cu3O6.9 (Tconset=94 K) subjected to radiation-induced disordering by a fast-neutron flux Φ to Tconset=68 K (Φ=7×1018 cm−2) and Tconset<4 K (Φ=12×1018 cm−2). It is found that as the structural disorder increases, the contribution of the indirect spin-spin interaction 63T2G−1, which is related to the value of the spin susceptibility at the boundary of the Brillouin zone of the copper planes χs(q={π/a; π/a}), decreases slightly at the transition to the superconducting state for the initial sample and remains unchanged for the weakly disordered sample. This behavior of the short-wavelength contribution to the spin susceptibility attests to the stability of the x2−y2 symmetry of the energy gap against structural disorder, in accordance with proposed theoretical models of Cooper pairing for high-Tc cuprates.
Jetp Letters | 2018
A. G. Smol’nikov; V. V. Ogloblichev; A. Yu. Germov; K. N. Mikhalev; Almaz F. Sadykov; Yu. V. Piskunov; A. P. Gerashchenko; A. Yu. Yakubovskii; M. A. Muflikhonova; S. N. Barilo; S. V. Shiryaev
For the first time, the CuFeO2 single crystal has been studied by 63,65Cu nuclear magnetic resonance (NMR). The measurements have been carried out in the temperature range of T = 100−350 K in the magnetic field H = 117 kOe applied along different crystallographic directions. The components of the electric field gradient tensor and the hyperfine coupling constants are determined. It is shown that electrons of copper 4s and 3d orbitals are involved in the spin polarization transfer Fe → Cu. The occupancies of these orbitals are estimated.
Physics of Metals and Metallography | 2014
K. N. Mikhalev; Z. N. Volkova; A. P. Gerashchenko
A brief survey of results concerning the study of manganites by the method of nuclear magnetic resonance (NMR) is presented. Experiments in which the nuclei of the majority of the elements that enter into the structural formulas of the manganites have been used as the local probes are considered. Primary attention is paid to the application of this local method for investigating the microscopic phase separation based on the data of the 55Mn NMR, orbital ordering in LaMnO3 based on the data of the 17O NMR, and low-frequency spin dynamics.
Journal of Experimental and Theoretical Physics | 2011
A. G. Smol’nikov; V. V. Ogloblichev; A. F. Sadykov; Yu. V. Piskunov; A. P. Gerashchenko; S. V. Verkhovskii; A. Yu. Yakubovskii; S. N. Barilo; G. L. Bychkov; S. V. Shiryaev
The NMR spectra and the decay of a spin echo signal from 51V nuclei in Kagome-staircase Co3V2O8 (CVO) and Ni3V2O8 (NVO) single crystals are measured in the temperature range 30–300 K and a magnetic field H0 = 20 kOe. The orientation dependences of the 51V NMR line shape are used to determine the electric field gradient (EFG) parameters, namely, quadrupole frequency νQ and asymmetry parameter η. These parameters for NVO and CVO are νQ = 180(10) kHz, η = 0.5(1) and νQ = 130(10) kHz, η = 0.6(1), respectively. A comparison of the results of calculating EFG tensors with a point charge model and the NMR data indicates that the crystallographically equivalent vanadium atoms in the Ni3V2O8 and Co3V2O8 compounds differ in the EFG axis orientation. M3V2O8 crystals are found to have vanadium positions (V1, V2) with different orientations of the z axis, which specifies the direction of the principal value of EFG (Vzz): these orientations lie in the bc plane and make an angle of either +51(5)° (V1) or −51(5)° (V2) with axis c. In the temperature range 30–300 K, the EFG tensor components and the local symmetry of the charge surrounding of the vanadium positions in NVO and CVO oxides are found to change insignificantly.