Conduction Electron Spin Resonance Linewidth Research Articles

Observation of conduction electron spin resonance in boron-doped diamond

We observe the electron spin resonance of conduction electrons in boron-doped (6400 ppm) superconducting diamond (${T}_{\text{c}}=3.8\phantom{\rule{0.28em}{0ex}}\text{K}$). We clearly identify the benchmarks of conduction electron spin resonance (CESR): the nearly temperature independent electron spin resonance signal intensity and its magnitude, which is in good agreement with that expected from the density of states through the Pauli spin susceptibility. The temperature dependent CESR linewidth weakly increases with increasing temperature, which can be understood in the framework of the Elliott-Yafet theory of spin relaxation. An anomalous and yet unexplained relation is observed between the $g$-factor, CESR linewidth, and the resistivity using the empirical Elliott-Yafet relation.

Features of electrical conductivity in an incommensurate phase of graphite intercalation compound C10HNO3

Electrical conductivity and conduction-electron spin resonance (CESR) have been studied in stage-2 acceptor α-graphite-nitric acid intercalation compound C10HNO3. It is found that the electrical conductivity σc along the c axis in the structurally incommensurate phase of this compound is temperature independent, whereas the electrical conductivity σa along carbon layers exhibits “metallic” temperature behavior. Analysis of the temperature dependences of σc, σa, and the CESR linewidth demonstrates that, in the incommensurate phase of the graphite intercalation compound, the electrical conductivity along the c axis is realized through a nonband mechanism—the transfer of free charge carriers along thin high-conductivity channels shunting the carbon layers adjacent to the intercalate.

In situ conduction ESR and theoretical studies of graphite intercalation by nitric acid

Results of an in situ conduction electron-spin resonance (CESR) study of HNO, molecule intercalation into highly oriented pyrolytic graphite (HOPG) plate with width being comparable with the graphite skin-depth governed by thec-axis conductivity are presented. The changes in the graphite CESR signal line shape, intensity and linewidth and the stepwise changes both of intensity and linewidth of CESR signal of intercalated sample were clearly detected during this reaction. Under the assumption that the graphite CESR signal evolution is caused by the advance of a boundary separating the intercalated and nonintercalated HOPG, the average value of spin reorientation probability during the collision of current carriers with this interface and the diffusion coefficient of nitric acid into the HOPG plate were extracted from experimental data. With the chemical potential versus intercalation time proposed by the authors for the experimental conditions, the stepwise changes of the CESR signal intensity of intercalated sample was calculated theoretically.

Phase transition induced current carrier injection phenomenon in graphite intercalation compounds

In graphite intercalation compounds C 20HNO 3 we have observed a similar dependence of conductivity, conduction electron spin resonance (CESR) linewidth and spin carrier concentration versus temperature. It was shown that the increase of conductivity and ‘nonmetallic’ broadening of the CESR linewidth observed at and after crystallization of the HNO 3 ‘guest’ molecules may be due to an increase in concentration of conduction electrons and a decrease in their mobility, respectively.

In situ ESR study of the HNO 3-Intercalate diffusion process in graphite intercalation compounds

In situ conduction electron spin resonance (CESR), contactless conductivity and X-ray diffraction studies of HNO 3 molecule intercalation into highly oriented pyrolytic graphite (HOPG) plates are presented. The CESR lineshape, linewidth, intensity and position analysis allow us to establish: a) individual reaction steps, b) two different intercalation mechanisms: a slow diffusion of the intercalate through faces parallel to the c-axis in the whole thickness of a sample and a relatively faster nucleation of a new phase in near surface galleries; c) an estimate of the constant of the two-dimensional diffusion of intercalate through the sample after its insertion into HOPG. Each of the intercalation mechanisms is characterized by an ‘induction period’, in which the graphite takes up comparatively little intercalate, and by an index of the stage appearing on its own.

Phase transitions and “nonmetallic” temperature dependence of conduction electron spin resonance line width in quasi-two-dimensional synthetic metal C 15HNO 3

In the synthetic metal C 15HNO 3 during and after crystallization of the HNO 3 “guest” molecules, the simultaneous increase of conductivity, conduction electron spin resonance (CESR) line width and spin carriers concentration ( N) was found and investigated. The increase of N is directly connected with the partial localization of the conduction π-electrons (in terms of graphite intercalation compounds tight binding model). Since the localized electrons are the perturbation centres for the conduction electrons, it has been proposed that the increase of their concentration is the main reason for the decrease of the in-plane spin carriers mobility and the “nonmetallic” increase of the CESR line width observed during and after crystallization of the HNO 3 “guest” layers.

Conduction electron spin resonance in Rb1C60 and Rb3C60

The conduction electron spin resonance (CESR) of Rb 3 C 60 has been observed, and the spin susceptibility is found to be X S =(12.4±4) × 10 −4 emu/mole, in agreement with the static measurements. The CESR linewidth of Rb 3 C 60 is 600G at room temperature. Formerly the ESR of Rb 1 C 60 has been erroneously assigned to Rb 3 C 60 . It has a width of 6.5G at 300K and shows the polymer to monomer transition at 400K. Below this temperature Rb 1 C 60 is a quasi-1D metal with a transition to a spin density wave ground state at 50K.

Conduction electron spin resonance in Rb3C60.

The conduction electron spin resonance (CESR) of Rb 3 C 60 has been observed for the first time and the spin susceptibility found to be χ s =(12.4±4)×10 -4 emu/mol, in agreement with static measurements. The CESR linewidth is anomalously large, 1300 G at 30 K giving a spin lattice relaxation rate T 1 -1 =9.0×10 -11 sec -1 , and we suggest that it is caused by large molecular disorder. The ESR line formerly assigned to Rb 3 C 60 arises from an unidentified nonsuperconducting phase Rb x C 60 which has a structural transition near 400 K and a thermal history dependent metal-insulator transition at lower temperatures

Observation of conduction electron spin resonance in the neodymium cerium copper oxide (Nd1.85Ce0.15CuO4-y) superconductor

Normal and superconducting Nd{sub 2{minus}x}Ce{sub x}CuO{sub 4{minus}y} (x = 0.00, 0.15) compounds have been studied by electron spin resonance (ESR). In contrast to previous reports that the high-temperature superconducting oxocuprate compounds are ESR silent, a conduction ESR (CESR) signal has been observed in the superconducting Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}y} compound. The temperature dependence of the CESR signal intensity, g value, and line width are consistent with a two-dimensional spin structure in Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}y}. A possible reason for the lack of a CESR signal in other high-temperature superconducting systems is that they have more efficient spin-lattice relaxation which is associated with CESR lines too broad to be detected. 14 refs., 4 figs.

Lineshape analysis of the 13C Overhauser shift in organic conductors and semiconductors

In organic conductors such as (fluoranthene)2PF6 or pyrene radical-cation salts, and organic semiconductors such as lithium phthalocyanine, a shift of the conduction-electron spin resonance (CESR) frequency is observed. This so-called Overhauser shift is significant compared with the CESR linewidth and is caused by the averaged hyperfine interaction between the conduction electrons and the nuclei. This shift can be measured using a double-resonance method, and it can be enhanced by two or three orders of magnitude by partially saturating the CESR. It provides a sensitive probe for the detection of nuclear magnetic resonance. Here we report on our measurements of the 13C induced Overhauser shift in the systems mentioned above. By means of a lineshape analysis of the 13C resonance curves, we investigated the distribution of the conduction electrons over these molecular systems.

Saturation with temperature of the electrical resistivity and the CESR linewidth in TiBe2

The electrical resistivity of TiBe2 shows anomalous behaviour at high temperature characterised by a strong reduction of the slope (d rho /dT); the authors interpret this in terms of a decoupling of the s- (or p-) like and d-like states and show that the corresponding s-d scattering resistivity rho sd tends to saturate above 300 K. The conduction electron spin resonance linewidth, which is due mainly to electron-lattice relaxation, is expected to vary like the resistivity and indeed they observe a sharp saturation of it above approximately=200 K indicating that it is more likely related to rho sd(or rho dd) rather than to the global resistivity; the saturation becomes less sharp if the residual resistivity increases, indicating a strong coupling, probably of the s-like electrons with the lattice via the local defects.

The effect of disorder on the conduction electron spin resonance linewidth of the α and β phases of (BEDT-TTF) 2I 3

We present the electron spin resonance linewidth of α and β phases of the organic conductor di- bis (ethylenedithiolo) tetrathiafulvalene driiodide [(BEDT-TTF) 2I 3] disordered by fast electron irradiation. In the high temperature metallic phase the linewidth decreases in both phases with defect concentration in contrast to the predictions of the Elliott mechanism for spin relaxation in metals.

Combined Effects of Impurity and Thickness on the Conduction Electron Spin Resonance Linewidth in Silver

The conduction electron spin resonance of silver foils doped with 10 ppm Au has been measured by the transmission method over the thickness range 5-66 µm in the temperature range between 18 K and 44 K at 22.7 GHz as functions of thickness and temperature. As a result of doping silver with Au, the spin-orbit parameter dominating the phonon-induced spin relaxation has not been changed significantly. On the other hand, the surface spin scattering probability e has increased from 6×10 -4 to 2×10 -3 . This increase with Au impurities has been attributed to the impurity-induced disorder of the silver surface.

An examination of the contributions to electron-spin scattering processes in aluminium

In an endeavour to understand the various contributions to the spin scattering of conduction electrons in aluminium, the conduction-electron spin resonance linewidths of polycrystalline, pure and dilute alloy foils of aluminium have been measured in reflection at 42.5 MHz, 9.27 GHz and 20.9 GHz, over the temperature range 4.2-100K. From these linewidths the phonon spin scattering contribution at 42.5 MHz and 9.27 GHz is obtained and is found to be proportional to the phonon contribution to the resistivity scattering. At 42.5 MHz and below 25K a temperature dependence proportional to T2 is recorded, indicative of an electron-electron scattering process. The probability of a spin flip when an electron collides with the surface is also calculated from measurements of the linewidth at 42.5 MHz, and is found to agree with earlier measurements. At higher frequencies there are other contributions to the linewidth which may be attributed either to the complex Fermi surface of aluminium or to the breakdown of motional narrowing by the conduction electrons of the g anisotropy over the Fermi surface. In pure samples, one contribution is found at low temperatures and is linearly dependent on both the observational frequency and the resistivity scattering time. A second contribution, which is also linearly dependent on the frequency but independent of temperature, is reported as well. Finally, at the highest frequencies used or at high impurity levels an extra contribution to the temperature dependence is found, which is evident even at temperatures as high as 100K where motional narrowing is expected to be complete.

On the spin-flip scattering of conduction electrons in small Li-Na particles studied by CESR

A reinterpretation is presented of recent results (Chizhov et al. 1982) on the conduction electron spin resonance (CESR) linewidths recorded from small lithium particles to which small levels c of sodium impurities have been added. This reanalysis demonstrates good agreement with contemporary understanding of interface spin scattering in bimetallic, layered, systems. It is shown that the sodium segregates out to the surface of the lithium particles. A maximum of three atomic layers of sodium on the surface gives rise to the observed spin-flip probability of the lithium conduction electrons at the surface, ϵ obs, being equal to ϵ Na where ϵ Na is the surface spin-flip probability for the sodium-vacuum interface. We approximate, for sufficient sodium impurities, ϵ obs = ϵ Na to σ sf, Li (Na)/ σ r, Li (Na) where σ sf, Li (Na) and σ r, Li (Na) are the spin-flip and resistivity scattering cross sections respectively for Na impurities in Li. From this relationship it is predicted that the amount of CESR linewidth broadening due to dissolved Na, is ΔB i (Na)/ c = 0.11 mT/at.%.

The effects of frequency, thickness and purity on the conduction electron spin resonance linewidth of silver foils

The conduction electron spin resonance (CESR) linewidth of polycrystalline pure silver foils and some of its dilute alloys have been measured from 4.2 to 25K at 40 MHz, 9.27 and 20.9 GHz. The spin-flip scattering cross sections are given for copper, palladium, platinum and gold in silver; these are found to be frequency independent. There is however, a frequency-dependent contribution to the linewidth for all purities which is found to be linearly dependent upon frequency and inversely proportional to the sample thickness. It is suggested that this frequency- and thickness-dependent term is dominated by surface roughness and, as such, is due to high-angle scattering at the surface. The mechanism provides rapid mixing of states on the Fermi surface necks, those with large spin-orbit coupling with the very nearly free electron states on the 'belly'. With careful removal of the residual linewidth contributions caused by impurities, defects and the surface, the intrinsic temperature-dependent portion of the CESR linewidth has been extracted. At very low temperatures this varies as exp(-T/120) which suggests once again the importance of high-angle scattering brought about by the few remaining high-energy phonons found at these temperatures. As the temperature is increased, normal spin-phonon scattering of the 'belly' electrons start to take over, thus overriding the significance of the high-angle scattering leading then to a T4 dependence, in approximate accordance with expectations from phonon scattering theory.

The Stage and Temperature Dependences of Conduction Electron Spin Resonance in Alkaline-Metal Graphite Intercalation Compounds

The stage ( N ) and temperature dependences of the conduction electron spin resonance (CESR) have been investigated for rubidium and potassium graphite intercalation compounds. The CESR line width ( Δ H ) has a minimum at N =2 and increases with stage number for N ≧3. The temperature dependence of Δ H for higher stage compounds of N ≧3 shows a remarkable increase at lower temperatures below 200 K. These features can not be understood by the ordinary theory, but they might be related to the electronic structure characteristic of higher stage compounds.

Conduction electron spin-flip scattering by impurities in copper

We have measured the concentration dependence of the transmission conduction electron spin resonance linewidth of copper doped with Li, Zn, Ga, Ge, As, Ni, and Ti. In each case, we find a linear concentration dependence which allows us to determine a spin-flip cross-section, σsf, for each impurity. These cross-sections, together with those deduced from linewidth data previously published for other impurities (both magnetic and not), form a useful body of results and allow one to test spin-flip scattering models. We find an overall agreement of our values for σsf for transition metal impurities with estimates based on the Friedel virtual bound state model, including a spin-orbit interaction. For specific impurities (Zn, Ga, Ge, and As) we find that σ sf is determined by the charge contrast between the impurity and the copper host as was noted earlier from similar studies based on Li and Na by Asik, Ball, and Slichter. A particular situation is present with Li as an impurity in copper, interpreted as a « spin-orbit hole », which, together with the other results, confirm that the spin-orbit difference between the impurity and the host is the relevant spin-orbit parameter for σsf.

Conduction electron spin disorientation at the surfaces of copper and silver

Results of the measurements of the residual conduction electron spin resonance linewidth in copper foils and silver foils and films are presented. From these results the probabilities of spin disorientation, epsilon , at the sample surface of both copper and silver are determined. For copper foils the value obtained is epsilon =(3.4+or-0.2)*10-4 whilst for silver foils and films it is found that epsilon =(4.6+or-0.2)*10-4 and epsilon =(5.9+or-0.6)*10-4 respectively. All these values fall substantially below those predicted from simple theory based on spin-orbit coupling. It is indicated that a reconsideration of previous epsilon interpretations is necessary.

Influence of frequency and temperature on the conduction-electron spin-resonance linewidth andgvalue in copper

The CESR linewidth and $g$ value of pure Cu is measured over the temperature range 4.2 to 50 K at the frequencies of 9.27, 21, and 59.6 GHz. The linewidth is shown to have a linearly frequency dependent, but temperature-independent term giving 0.040\ifmmode\pm\else\textpm\fi{}0.002 mT/GHz. A second term, when ascribed to partial breakdown of motional narrowing, is found to be much weaker than proposed elsewhere. The $g$ value is found also to be temperature and frequency dependent.