共查询到20条相似文献,搜索用时 15 毫秒
1.
S. V. Demishev A. L. Chernobrovkin E. A. Goodilin V. V. Glushkov A. V. Grigorieva N. A. Samarin N. E. Sluchanko A. V. Semeno Yu. D. Tretyakov 《固体物理学:研究快报》2008,2(5):221-223
Basing on the high frequency (60 GHz) electron spin resonance study of the VOx multiwall nanotubes (VOx ‐NTs) carried out in the temperature range 4.2–200 K we report: (i) the first direct experimental evidence of the presence of the antiferromagnetic dimers in VOx ‐NTs and (ii) the observation of an anomalous low temperature growth of the magnetic susceptibility for quasi‐free spins, which obey the power law χ (T)~1/T α with the exponent α ≈ 0.6 in a wide temperature range 4.2–50 K. We argue that the observed departures from the Curie–Weiss behaviour manifest the onset of the quantum critical regime and formation of the Griffiths phase as a magnetic ground state of these spin species. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
Electron spin resonance and magnetic susceptibility suggest superconductivity in Na doped WO3samples
A. Shengelaya S. Reich Y. Tsabba K.A. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):13-15
In WO3 doped with Na (WO3:Na) an Electron Spin Resonance (ESR) signal with unresolved fine and/or hyperfine structure is detected and used as a probe
for the state of the carriers. Using the saturation method we determined the spin-lattice relaxation rate 1/
T
1
of these paramagnetic centers. Upon cooling below 100 K, 1/
T
1
decreases markedly, as known to occur in NMR when a gap opens in the superconducting state. At low temperatures, 1/
T
1
quantitatively follows BCS behavior with a gap K or 2 . The magnetic susceptibility exhibits a strong difference between magnetic-field cooled and zero-field cooled regimes below
which also supports a so far unknown superconducting phase resulting from Na doping.
Received 14 April 1999 and Received in final form 6 September 1999 相似文献
3.
M. Burggraf H. Dragan P. Gruner-Bauer H. W. Helberg W. F. Kuhs G. Mattern D. Müller W. Wendl A. Wolter E. Dormann 《Zeitschrift für Physik B Condensed Matter》1995,96(4):439-450
Crystal structure, microwave conductivity and static magnetic susceptibility were analyzed for the conducting perylene (PE) radical cation salts of nominal composition (PE)2(PF6)1–x
(AsF6)
x
·2/3 THF for 0x1. Crystallographic phase transitions in the high-temperature metal phase were also characterized by differential scanning calorimetry and electron spin resonance. The Peierls transition occuring at 100–120 K (depending onx) and the opening of the energy gap in the semiconductor phase were determined from the magnetic data. The dependence of these properties on the size of the complex anions and the packing of the PE molecules is discussed. 相似文献
4.
Antiferroelectric spin wave resonance (AFESWR) and electric spin moment, mathematically predicted by Dirac, were identified for the first time. It has also been found, in addition to well-known SSH-model, that topological quasiparticles, called σ-quasiparticles, can be formed in CC σ-bonds of organic polymers. Topological σ-polaron lattice is proposed to be responsible for the observed AFESWR both in starting polyvinylidene fluoride (PVDF) films and in carbynoid films, which are the products of PVDF-dehydrohalogenation. Dynamical systems of σ-polarons and π-solitons, identified in the samples studied, are substantionally nonlinear and can be registered in stochastic regime by usual IR absorption measurements. 相似文献
5.
6.
7.
EPR study of the low temperature ferroelectric phase transition in Cu doped Rb2ZnCl4 single crystals
Mariana Stefan Sergiu V. Nistor Dirk SchoemakerIoan Ursu 《Solid State Communications》2003,127(11):695-698
Temperature dependent EPR measurements on copper doped Rb2ZnCl4 single crystals allowed us to evidence and study the P21cn↔C1c1 structural phase transition that takes place in this compound at 74.6 K. From the two types of Cu2+ centers localized at different anionic sites, called Cu2+(I) and Cu2+(II), which are formed in this compound, only the Cu2+(II) centers exhibit observable changes in their EPR spectra, attributable to the symmetry lowering. The observed changes have been related to the soft-mode responsible for the structural phase transition. 相似文献
8.
The structural, transport and electron spin resonance properties of bulk and nanosized La0.875Sr0.125MnO3 prepared by a sol-gel method have been investigated. The bulk sample has an orthorhombic structure and a ferromagnetic insulating ground state. The ESR spectra indicate the coexistence of the ferromagnetic insulating and ferromagnetic metallic phases below TC. In addition to a sharp peak in the vicinity of TC, another sharp peak close to is clearly observed in the intensity of the spectra, which may be correlated with the structural transition and orbital ordering at this temperature. For the nanosized sample, a drastically different behavior is found. With a rhombohedral structure down to 70 K, the nanosized sample shows a ferromagnetic metallic ground state. The ESR studies reveal the coexistence of the paramagnetic and ferromagnetic resonance signals. The resonance intensity shows a broad peak around 200 K, which may be due to the wide ferromagnetic transition in the nanoparticle. 相似文献
9.
We have studied [N(C2H5)4]2MnCl4 crystal by X-band CW EPR spectra in the temperature range 170-300 K. The angular dependences of linewidth ΔH were measured and described in the light of a double-layer system (2D) with exchange interactions. Two temperature anomalies of linewidth ΔH were found at T1=225 K and T2=192 K on cooling. Different behaviors of ΔH anomalies recorded for an external magnetic field parallel and perpendicular to the ab crystallographic plane indicate ordering/disordering of MnCl4 groups in this plane and their displacement along the c-axis which occurs in the temperature of about 225 K. 相似文献
10.
K.J. White 《Journal of Physics and Chemistry of Solids》1973,34(2):283-293
Electron spin resonance (ESR) studies have been carried out on the radicals produced by the γ-irradiation of single crystals of KMnO4.Analysis of the data yields at least two paramagnetic species. The first radical is produced by room temperature irradiation and gives a single line for each of two inequivalent magnetic sites. There is no resolvable hyperfine structure and the g tensor for the species is given by, gb = gμ′ = 2·0176, gx′ = 2·0020, gz′ = 2·0112. The spectrum is tentatively assigned to the O3? radical although MnO2 and MnO4 are also possibilities.The second radical is produced by irradiation at 77°K and the spectrum disappears irreversibly at slightly higher temperatures. Analysis of the very complicated spectra yields, gb = 1·9617, gx = 1·9452, gu = 1·9940, Ab = 386 MHz, A2 = 87 MHz, A3 = 20 MHz. This spectrum is assigned to the MnO4?2 radical. The relationship of the radicals observed to the effect of high energy radiation on the decomposition of KMnO4 in the light of current solid state theory is discussed. 相似文献
11.
P.J. von Ranke N.A. de Oliveira V.S.R. de Sousa A. Magnus G. Carvalho 《Journal of magnetism and magnetic materials》2010,322(1):84-87
In this work we present a model to describe the magnetocaloric effect (MCE) in ferrimagnetic arrangements. Our model takes into account the magnetoelastic interactions in the two coupled magnetic sublattices, which can lead to the onset of the first order magnetic phase transition and the giant-MCE. Several profiles of the MCE, such as: the inverse- and giant-MCE were systematically studied. Application of the model to the ferromagnetic compounds GdAl2, Gd5(Ge1.72Si2.28), Gd5(Ge2Si2), and to the ferrimagnetic compound Y3Fe5O12 was performed, showing a good agreement with the experimental data. 相似文献
12.
V. A. Atsarkin V. V. Demidov G. A. Vasneva D. G. Gotovtsev 《Applied magnetic resonance》2001,21(2):147-156
With original modulation technique, the longitudinal electron spin-relaxation timeT 1 has been measured in the La1-xCaxMnO3 manganite (x = 0.1) both in the paramagnetic state and around the temperature (T c) of the ferromagnetic ordering. The data are compared with the evolution of the transverse relaxation time T2 as determined from the electron spin resonance (ESR) linewidth. Well above Tc, theT 1 =T 2 equality was confirmed, whereas a steep slowing down ofT 2 was observed asT c was approached (theT 1/T2 ratio increased by two orders of magnitude). The temperature dependence ofT 1 within the whole temperature range was found to be consistent with that ofT · χ(T), where χ(T) is the electron-spin susceptibility obtained from the ESR absorption area. The interpretation suggests that both the longitudinal and transverse electron-spin relaxation rates are governed by strong exchange interaction between the Mn ions, the ESR linewidth being inhomogeneously broadened in the vicinity of the phase transition. 相似文献
13.
This article reviews the various EPR (CW, pulsed and time-resolved) and μSR studies reported in C60/C70/C82 fullerenes. Different techniques for preparing paramagnetic C60/C70 species giving an EPR signal have been included. This literature survey is complete from the beginning of fullerene research (1985) up to middle 1994. 相似文献
14.
Electron spin resonance spectra of chromia-yttria solid solutions have been studied at room temperature for Cr concentrations between 0.20 and 2.00 mol%. Isolated Cr3+ ions in sites with two different symmetries were observed, as well as well as Cr3+ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Cr3+ ions decreases with increasing chromium concentration. The results are consistent with the assumption that the chromium ions occupy preferentially the C2 symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Cr3+ ions of 0.64 nm, of the same order as that of Cr3+ ions in MgO. 相似文献
15.
SiC thin films were grown on Si (1 0 0) substrates by excimer laser ablation of a SiC target in vacuum. The effect of deposition temperature (up to 950 °C), post-deposition annealing and laser energy on the nanostructure, bonding and crystalline properties of the films was studied, in order to elucidate their transition from an amorphous to a crystalline phase. Infra-red spectroscopy shows that growth at temperatures greater than 600 °C produces layers with increasingly uniform environment of the Si-C bonds, while the appearance of large crystallites is detected, by X-ray diffraction, at 800 °C. Electron paramagnetic resonance confirms the presence of clustered paramagnetic centers within the sp2 carbon domains. Increasing deposition temperature leads to a decrease of the spin density and to a temperature-dependent component of the EPR linewidth induced by spin hopping. For films grown below 650 °C, post-deposition annealing at 1100 °C reduces the spin density as a result of a more uniform Si-C nanostructure, though large scale crystallization is not observed. For greater deposition temperatures, annealing leads to little changes in the bonding properties, but suppresses the temperature dependent component of the EPR linewidth. These findings are explained by a relaxation of the stress in the layers, through the annealing of the bond angle disorder that inhibits spin hopping processes. 相似文献
16.
Electron paramagnetic resonance and optical absorption spectra of Cr ions in cadmium phosphate glass
R.V.S.S.N. Ravikumar Ryuichi KomatsuKo. Ikeda A.V. ChandrasekharB.J. Reddy Y.P. ReddyP.S. Rao 《Solid State Communications》2003,126(5):251-253
EPR and optical absorption investigations of chromium doped cadmium phosphate glass are carried out. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. From the results and analyses of the EPR and optical studies, the site symmetry of Cr3+ ion in the glass is ascribed to a distorted octahedron. The bonding parameters suggest the ionic nature of Cr3+ ion with the ligands. 相似文献
17.
N. Guskos V. Likodimos S. Glenis J. Typek H. Fuks M. Wabia D.G. Paschalidis D. Tossidis C.L. Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):277-282
The magnetic properties of the rare earth molecular compounds with hydrazone ligands containing Nd3+, Gd3+, and Yb3+ have been investigated by electron paramagnetic resonance (EPR) and magnetization measurements. For the Gd-compound, partially
resolved fine structure due to Gd3+ and exchange narrowing effects at low temperatures are observed in the EPR spectra, suggesting, consistent with the EPR and
dc magnetic susceptibility, weak antiferromagnetic exchange interactions. Paramagnetic behavior sustained down to low temperatures
is derived for Yb3+ ions, whereas substantial ferromagnetic exchange coupling is inferred for the lighter Nd3+ ions, indicating significant variations of the exchange integrals along the lanthanide series.
Received 29 April 2002 Published online 31 July 2002 相似文献
18.
S. Bandow F. Kokai K. Takahashi M. Yudasaka S. Iijima 《Applied Physics A: Materials Science & Processing》2001,73(3):281-285
The magnetic properties of single-wall carbon nanohorns (SWNH) were studied by electron spin resonance (ESR) and static magnetic
susceptibility measurements. The SWNHs were ESR active with linewidth (ΔH) of ∼6 G in vacuo at room temperature. ΔH was susceptible
to the partial pressure of O2 and became 53 G at 1 atmospheric pressure of O2, while the integrated ESR intensity was independent on O2 pressure and behaved as Curie-like, suggesting an intrinsic ESR origin with localized electron spin character. The diamagnetic
susceptibility for SWNHs indicated a value smaller than that of randomly oriented graphite by an order of magnitude, but showing
a magnitude comparable to those of C60 and C70. It is suggested that the large diamagnetism expecting for sp2 networked carbon materials will be canceled by the Van Vleck constant paramagnetism.
Received: 20 November 2000 / Accepted: 21 November 2000 / Published online: 25 July 2001 相似文献
19.
Electron spin resonance indication of the ferromagnet-spin glass transition in amorphous FeMn alloys
T.F. Rosenbaum L.W. Rupp G.A. Thomas W.M. Walsh H.S. Chen J.R. Banavar P.B. Littlewood 《Solid State Communications》1982,42(10):725-727
We find that ESR linewidth measurements of amorphous FeMn alloys indicate the ferromagnet-spin glass transition temperature without a scaling analysis. Comparison with neutron scattering data shows the importance of studying the long-wavelength limit. 相似文献
20.
We present Electron-Spin-Resonance experiments in the frequency range 35–420 GHz in magnetic fields up to 14 T and with temperatures down to 1.5 K. The quasi-onedimensionalS=1 Spin Systems NENP and NINO exhibit similar resonance-modes, which can be associated with transitions between excited states atq= and excitations from the groundstate. Groundstateexcitation can be explained with regard to a transverse staggered field due to inequivalent Ni2+-sites along the chains. Several features are discussed like polarisation-and temperature dependence of line-intensity and the angular and temperature-dependence of resonance-field. 相似文献