Local moment spin resonance in a superconductor

The ESR of Gd in CeRu₂ and LaRu₂ has been observed in the normal and superconducting state. The temperature dependence of the linewidth in the superconducting state follows a trend expected from NMR measurements in superconductors.     

Local moment spin resonance in a Kondo system

The ESR of the system $\text{Yb:}\text{Au}{}_{\mathrm{x}}\text{Ag}{}_{\mathrm{1?x}}$ has been investigated for 0.7 ? x ? 1. The g-shift (Δg) and the temperature derivative of the linewidth $\text{(}\text{ΔH}\text{ΔT}\text{)}$ increase with decreasing Au concentration. For T ? 2°K effects in $\text{(}\text{ΔH}\text{ΔT}\text{)}$ are observed, which are attributed to the Kondo effect.     

Theory of spin diffusion in liquid-phase polymer systems

A general theory of spin diffusion in condensed media is constructed by the method of Zwanzig-Mori projection operators using the superpositional approximation to decouple the many-particle correlation functions. The spin diffusion coefficient is expressed in the form D _sp=D _tr+D _f , where D _tr is the contribution associated with translational displacements of the molecules and D _f is the contribution caused by intermolecular flip-flop processes. The expression for D _tr differs from the well-known Kubo-Green formula for the self-diffusion coefficient D _sd in that the integrand contains an additional factor P _f (t), which is the probability of the molecular spins not participating in intermolecular flip-flop transitions over the time t. A microscopic expression is obtained for D _f in the form of a time integral of the intermolecular dipole-dipole dynamic correlation functions. For liquid-phase polymer system with fairly high molecular mass the condition D _sp≫D _sd is satisfied. Zh. éksp. Teor. Fiz. 114, 538–554 (August 1998)     

Effect of rf field on spin diffusion

A study was made of the effect of an rf field on spin diffusion. The interaction of spins with the rf field is described quantum mechanically. It is shown that the effect of the rf field on the system of spins can, in some approximation, be interpreted as the effect of a change in the Larmor frequency of the spin and a decrease in the magnitude of the dipole-dipole interaction between spins. These conclusions were obtained on the basis of a unitary transformation which eliminates the explicit form of the spin-photon interaction operator in the Hamiltonian of the system considered. An expression is derived for the spin-diffusion coefficient under saturation. The presence of the rf field results in a decrease in the diffusion coefficient.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 7–11, September, 1979.     

Effect of local anisotropy on spin glass

The effects of uniaxial crystal field on spin glass properties are investigated. The parallel susceptibility (χ∥) exhibits sharper cusp than the perpendicular one (χ⊥).     

Temperature-induced local magnetic moment in narrow band electron systems

It is pointed out that the local spin fluctuations in certain exchange- enhanced paramagnetic metals can grow rapidly with temperature up to saturation, where the spin fluctuations may be regarded as arising from a set of local magnetic moments. Physical consequences of this phenomenon are discussed referring to experimental results.     

扭转超声振动系统中局部共振的研究

本文从扭转振动波动方程出发，推导出了具有类圆锥过渡段的复合阶梯型扭转变幅杆的频率方程解析表达式。从实验和理论上对该复合变幅杆的谐振频率随杆细端长度和直径的变化进行了测量和计算。通过对比，证明了复合振动系统中局部扭转共振现象的存在，并得到了其产生条件。     

核磁共振中的量子控制

近年来, 随着量子信息科学的发展, 对由量子力学原理描述的微观世界的主动调控已成为重要的前沿研究领域. 为构造实际的量子信息处理器, 一个关键的挑战是: 如何对处于噪声环境下的量子体系实现一系列高精度的任意操作, 以完成目标量子信息处理任务. 为此, 人们将经典系统控制论的思想方法延伸到量子体系的领域, 提出了大量的量子控制方法以及相关的数值技术(如量子优化控制、量子反馈控制等), 并取得了丰富的研究成果. 核磁共振自旋体系具备成熟的系统理论和操控技术, 为量子控制方法的实用性研究提供了优秀的实验测试平台. 因此, 基于核磁共振的量子控制成为量子控制领域的重要方向. 本文简要介绍了量子控制的基本概念和方法; 从系统控制论的角度对核磁共振自旋体系的基本原理和重要控制任务做了阐述; 介绍了近些年来在该领域发展的相关控制方法及其应用; 对基于核磁共振体系的量子控制的进一步的研究做了几点展望.     

The limit diffusion mechanism of relaxation for spin systems

The diffusion limit theorem for stochastic differential equations is applied to analyse the dynamical evolutions of spin systems. Bloch equations are derived and the stability of asymptotic evolutions is proved. The theory is applied to nuclear magnetic relaxation of two spins.     

Nuclear magnetic resonance and spin relaxation in biological systems

Proton nuclear spin-lattice relaxation in biological systems is generally distinguished from that in inorganic systems such as rocks by the presence of locally disordered macromolecular environments. Rapid exchange of readily observed labile small molecules among differently oriented macromolecular sites generally nearly averages the spectral anisotropies in the small molecule resonances. The biological tissue is generally distinguished from the inorganic matrix by the presence of a significant population of protons in the solid components that are well connected by dipolar spin couplings. Magnetic coupling between the solid and the liquid components generally dominates the magnetic field dependence of the spin-lattice relaxation rates observed in the small molecule components which is generally described by a power law in the Larmor frequency. Recent theory involving a modification of the spin-phonon class of relaxation mechanism provides a quantitative understanding of these data in terms of the dynamics of the chain molecules generally present in the solid spin systems, folded proteins for example.     

Electron spin resonance of ion-implanted Si:P systems

The ESR of Si:P and (Si:P):Sb systems made by ion implantation has been observed. An anomalous line-broadening appears in the (Si:P):Sb system, and is considered to be due to the large spin-orbit interaction of Sb donor impurity. The effective spin-lattice relaxation time, T_1eff, of both the systems is found to be dominated by a thin layer with the shortest relaxation time T₁(χ).     

Relaxation effects in weakly-coupled three spin systems by double resonance

Nuclear magnetic double-resonance spectra of weakly-coupled spin systems exhibit several interesting features. The effect of relaxation on the symmetry properties of double resonance spectra of weakly-coupled spin systems is investigated using spin inversion operators. The double-resonance spectra of the AX₂ type systems formed by the protons in (I) 1,1,2-trichloroethane and in (II) 2,2-dichloroethanol (excluding the hydroxyl proton) exhibit these symmetry effects. In both these molecules relaxation is contributed by several mechanisms. In sample II the effect of the exchanging proton in the hydroxyl group is also considered and the exchange time is estimated.     

Conduction electron spin resonance as a probe of zinc diffusion in lithium films

CESR is used to measure the maximum solubility C₀ and the diffusion constant D of zinc in lithium. The sample is a bimetallic layer obtained by thermal evaporation. The first deposited metal (zinc) is 300 Å thick, the second (lithium) 2μm thick. We analyze the resonance lineshape, taking into account the zinc diffusion via the Fick theorem. From the variations of the Li resonance linewidth as a function of time, we measure C₀ = 50 ppm and D = 160 Ų sec^-1 at room temperature.     

Electron spin resonance of symmetrical three-spin systems in nematic liquid crystals

An E.S.R. line-shape model is developed for fast tumbling three-spin systems in nematic liquid crystals. The line positions are calculated from a spin hamiltonian, which considers Zeeman, exchange, dipolar and hyperfine interactions of the three unpaired electrons. The dominant spin relaxation process, determining the line-widths, is assumed to result from the anisotropy of the zero-field splitting coupled to the molecular motion. The predictions of the theory are tested by comparison with the temperature-dependent E.S.R. spectra of trisverdazyl radicals in 4,4′-azoxydianisole. Good agreement is found between experimental and simulated spectra. A detailed analysis provides values for the solute order parameters [Pbar] ₂ and [Pbar] ₄. They correspond surprisingly well to predictions of the molecular-field theories of nematic liquid crystals.     

Relevance of ferromagnetic correlations for the electron spin resonance in Kondo lattice systems

Electron spin resonance (ESR) measurements of the ferromagnetic (FM) Kondo lattice system CeRuPO show a well defined ESR signal which is related to the Ce3+ magnetism. In contrast, no ESR could be observed in the antiferromagnetic (AFM) homologue CeOsPO. Additionally, we detect an ESR signal in ferromagnetic YbRh while it was absent in a number of Ce or Yb intermetallic compounds with dominant AFM exchange. Thus, the observation of an ESR signal in a Kondo lattice is neither specific to Yb nor to the proximity to a quantum critical point, but seems to be connected to the presence of FM fluctuations. These conclusions not only provide a basic concept to understand the ESR in Kondo lattice systems even well below the Kondo temperature (as observed in YbRh2Si2) but point out ESR as a prime method to investigate directly the spin dynamics of the Kondo ion.     

Effect of spin flip-flop on electron-spin-echo decay due to instantaneous diffusion

The effect of electron spin flip-flop on two- and 2 + 1-pulse electron-spin-echo decay due to instantaneous diffusion was studied on hydrogen atoms in y-irradiated quartz. The observed decay was slower than the theoretical decay including no spin flip-flop, and the discrepancy increased with the concentration of the hydrogen atoms. A comparison of the theoretical and the experimental decay rates revealed that the main factor diminishing the effect of instantaneous diffusion is not the direct flip-flop between on-resonant spins, but the fluctuation of the local magnetic fields for on-resonant spins due to the flip-flop of adjacent spin pairs.