66 research outputs found
Осаждение наноразмерных пленок полимера методом электронно-лучевого диспергирования политетрафторэтилена в вакууме на поверхность трековой мембраны
Исследованы структурные и электрохимические свойства композитных мембран, образующихся при осаждении на поверхность полипропиленовой трековой мембраны слоя полимера, полученного электронно-лучевым диспергированием политетрафторэтилена в вакууме
Electron-spin-resonance in the doped spin-Peierls compound Cu(1-x)Ni(x)GeO3
ESR-study of the Ni-doped spin-Peierls compound CuGeO3 has been performed in
the frequency range 9-75 GHz. At low temperatures the g-factor is smaller than
the value expected for Cu- and Ni-ions. This anomaly is explained by the
formation of magnetic clusters around the Ni-ions within a nonmagnetic
spin-Peierls matrix. The transition into the AFM-state detected earlier by
neutron scattering for doped samples was studied by means of ESR. For x=0.032 a
gap in the magnetic resonance spectrum is found below the Neel temperature and
the spectrum is well described by the theory of antiferromagnetic resonance
based on the molecular field approximation. For x=0.017 the spectrum below the
Neel point remained gapless. The gapless spectrum of the antiferromagnetic
state in weekly doped samples is attributed to the small value of the Neel
order parameter and to the magnetically disordered spin-Peierls background.Comment: 16 pages, LATEX, 12 figures, submitted to Journal of Physics :
Condensed Matte
Magnetic Resonance of the Intrinsic Defects of the Spin-Peierls Magnet CuGeO3
ESR of the pure monocrystals of CuGeO3 is studied in the frequency range 9-75
GHz and in the temperature interval 1.2-25 K. The splitting of the ESR line
into several spectral components is observed below 5 K, in the temperature
range where the magnetic susceptibility is suppressed by the spin-Peierls
dimerization. The analysis of the magnetic resonance signals allows one to
separate the signals of the S=1/2- and S=1 defects of the spin-Peierls phase.
The value of g-factor of these signals is close to that of the Cu-ion. The
additional line of the magnetic resonance is characterized by an anomalous
value of the g-factor and by the threshold-like increase of the microwave
susceptibility when the microwave power is increasing. The ESR signals are
supposingly attributed to two types of the planar magnetic defects, arising at
the boundaries of the domains of the spin-Peierls state with the different
values of the phase of the dimerization.Comment: LATEX-text, 12 PS-figures, typos corrected, LATEX-style change
Spin Transition Diagram of (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)] Studied by EPR
The high-spin↔ low-spin transition in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)] was studied by EPR under hydrostatic pressure in the temperature range of 80-310 K. Two modifications of the low-spin complexes: low-pressure (LS-1) and high-pressure (LS-2) ones were revealed. The low-spin complexes are associated in domains. Under atmospheric pressure LS-1 appears or disappears at 220 K. The hydrostatic pressure shifts the transition to high temperatures. Above 410 MPa the abrupt changes of the g-factor and width Δ B of the EPR line are observed. The pressure-induced transition LS-1 ↔ LS-2 is almost independent of T up to 275 K where under pressure 420 MPa a triple point is observed. When the pressure has been decreased the reverse transition from LS-2 to LS-1 or to high spin phase (at T>260 K) occurs with a large hysteresis about 95 MPa
Intramolecular and Lattice Dynamics in VV O(OCH) Crystal
Multi-nuclear mixed-valence clusters VVO(OCH) were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four V ions with individual spin S=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150 cm and the double jump one resulting in dynamics. The dependence of the transition ratesν on the energy of the total spin states was observed. In particular, in the range 300-220 K theν ≈0.7×10 cm and below 180 K the ν≈1×10 cm was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial V ions localization was discovered
Characteristics of the structural properties and the electric conductivity in LaSrAl1−x NixO4 ceramics caused by the Jahn-Teller effect
The Origin of EPR Signals in SrCuO Ceramics
The origin and thermal evolution of the EPR signals in SrCuO ceramics are studied. It has been shown that the EPR signals observed in this ceramic material are due to contamination with other phases. The axial signal is due to SrCu(OH)·HO, which is a product of water reactions with SrCuO
EPR Study of Water Induced Decomposition of the SrCuO and SrCuO Ceramics Surface. The Role of Carbon Dioxide
Processes of SrCuO and SrCuO ceramics decomposition induced by contact with water and carbon dioxide were studied by EPR. The dominant signals in the spectra were found to originate from SrCu(OH) (for SrCuO) and SrCu(OH)·HO (for SrCuO) compounds. The thermally induced conversion of SrCu(OH)·HO into SrCu(OH) was analysed, and its product CuO was found to exist in the nanocrystalline form. The presence of CO, reacting with Sr(OH), was shown to modify the decomposition process leading to the appearance of SrCu(OH)·HO, some hydroxycarbonates and Cu(OH) on the surface of ceramics studied. At temperatures higher than 300ºC CuO reacts back with Sr(OH). For the samples being in contact with atmospheric moisture this compound, deposited on a surface of SrCuO, decomposes to SrCu(OH). The presence of the antiferromagnetic compounds Cu(OH), CuO, and Cu[(OH)CO] in the samples can influence the results of magnetic measurements of the studied ceramics
EPR Discovery of a New Pressure-Induced Low-Spin Phase in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa) 2
Electron paramagnetic resonance studies of the high-spin (HS) ↔ low-spin (LS) transition in 2-methyl-5-ethyl-pyridine-5-chloro-salicylalt hiosemicarbazonatoferrate(III) performed under hydrostatic pressure up to 500 MPa in a temperature range of 80-310 K have revealed two modifications of the low spin complexes: low-pressure (LS1) and high-pressure (LS2) ones. Under atmospheric pressure LS1 appears on cooling and disappears on heating at 220 K. The hydrostatic pressure shifts the transition to higher temperatures. Below 275 K an increase in pressure to 410 MPa results in abrupt changes in the g-factor and widthΔ B of the EPR line indicating a transition to a new phase. The pressure-induced transition LS1 ↔ LS2 is almost independent of T up to 275 K, where at a pressure of 420 MPa a triple point is observed. The LS1↔ LS2 and HS↔ LS2 (at T>260 K) transitions occur with a large hysteresis of about 95 MPa. The process of the spin transition has been shown to begin with the formation of domains of LS complexes in the matrix of HS ones. The response of the domains to external factors has been studied
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