Monte Carlo Simulation Study on Domain Formation in the Photoinduced Low-Spin High-Spin Transition

The domain formation process of the photo-induced cooperative low-spin (LS) to high-spin (HS) conversion phenomena are studied based on the Monte Carlo simulation method. The existence of the threshold light intensity and the incubation period are demonstrated. It is pointed out that the nucleation barrier of HS domain is surmounted by the fluctuation caused by the repetition of excitation and de-excitation. By defining an effective temperature for this fluctuation, the time scale of incubation period is estimated following the usual domain formation theory. It grossly accounts the Monte Carlo (MC) results in three-dimensional cases. The phase separation of HS and LS domain is reproduced by considering the volume striction effect. The step wise abrupt conversion is ascribed to the de-pinning of the volume striction.     

Spin–Spin Interactions and Nuclear Magnetic Relaxation in Magnetic Solids

The influence of the orientational fluctuations of the electronic magnetization, which modulate nuclear spin–spin interactions (Suhl–Nakamura and dipole–dipole), on the spin-lattice relaxation of magnetic nuclei with spin I = 1/2 in the magnetically ordered solids has been investigated. It has been shown that this mechanism of the spin-lattice relaxation is less effective in comparison with the process of spin-lattice relaxation caused by the direct fluctuations of hyperfine fields, which appear when there are the fluctuations of electronic magnetization direction.     

Spin Noise Spectroscopy in N-GaAs:Spin Relaxation of Localized Electrons

Spin noise spectroscopy(SNS) of electrons in n-doped bulk GaAs is studied as functions of temperature and the probe-laser energy. Experimental results show that the SNS signal comes from localized electrons in the donor band. The spin relaxation time of electrons, which is retrieved from the SNS measurement, depends on the probe light energy and temperature, and it can be ascribed to the variation of electron localization degree.     

106Ag高自旋态结构

利用能量为60MeV的¹¹B束流, 通过¹⁰⁰Mo(¹¹B,5n)¹⁰⁶Ag熔合蒸发反应布居¹⁰⁶Ag的高自旋态, 用15台带BGO反康的HPGe探测器进行在束γ谱学测量. 通过γ-γ符合矩阵开窗分析和DCO比值分析, 建立了¹⁰⁶Ag新的能级纲图, 增加了26条新的γ跃迁和10条新能级. 通过与其相邻同位素奇奇核的系统比较, 对¹⁰⁶Ag的4条转动带的组态及结构性质进行了初步讨论.     

Spin Parity Effect on Magnetic Relaxation by Quantum Tunneling in Nanomagnets

Spin parity effect on magnetic relaxation by quantum tunneling in the biaxial spin model is studied by taking into account the transverse local stray field. It is shown that the square root time dependence in the even resonance occurs in the presence of a distribution of transverse anisotropic parameters, while the odd resonance always shows exponential relaxation. Magnetic relaxation under a sweeping field is also studied. The variation of the relaxation curve with the increasing distribution width of the local stray field for even resonance is qualitatively different from that of the odd resonance. The theoretical result on even resonance is in agreement with experimental results on Fe₈ system, while the prediction for odd resonance awaits the experimental verification.     

Spin Parity Effect on Magnetic Relaxation by Quantum Tunneling in Nanomagnets

Spin parity effect on magnetic relaxation by quantum tunneling in the biaxial spin model is studied by taking into account the transverse local stray field. It is shown that the square root time dependence in the even resonance occurs in the presence of a distribution of transverse anisotropic parameters, while the odd resonance always shows exponential relaxation. Magnetic relaxation under a sweeping field is also studied. The variation of the relaxation curve with the increasing distribution width of the local stray field for even resonance is qualitatively different from that of the odd resonance. The theoretical result on even resonance is in agreement with experimental results on Fe8 system, while the prediction for odd resonance awaits the experimental verification.     

Spin Relaxation in the quantized Hall regime in the presence of disorder

We study the spin relaxation (SR) of a two-dimensional electron gas in the quantized Hall regime and discuss the role of spatial inhomogeneity effects on the relaxation. The results are obtained for small filling factors ν?1) or when the filling factor is close to an integer. In either case, SR times are essentially determined by a smooth random potential. For small n, we predict a “magneto-confinement” resonance manifested in the enhancement of the SR rate when the Zeeman energy is close to the spacing of confinement sublevels in the low-energy wing of the disorder-broadened Landau level. In the resonant region, the B-dependence of the SR time has a peculiar nonmonotonic shape. If ν?2n+1, the SR is going nonexponentially. Under typical conditions, the calculated SR times range from 10^?8 to 10^?6 s.     

Spin Relaxation in Single-Ion Magnets under the Slowing Down Effect Produced by the Stray Field of Ferromagnetic Microparticles

JETP Letters - The quantum tunneling of magnetization accelerates magnetic relaxation in transition and rare-earth ion complexes and often leads to the degradation of the characteristics of...     

Relaxation Processes at High Levels of Vibrational Excitation of Polyatomic Molecules in the Ground Electronic State

By the spectral and kinetic characteristics of the luminescence of vapors of polyatomic molecules (anthracene, anthraquinone, fluorenone) initiated by selective IR multiphoton excitation (IR MPE) of molecules in the ground electronic state S ₀ the relaxation processes proceeding under vibrational excitation of molecules to energies exceeding the energies of the lower excited electronic states have been investigated. The changes in the spectral and kinetic characteristics with increasing CO₂ laser energy density and vapor P _v and foreign gas pressure P _FG are analyzed. They are similar to the characteristics obtained for normal fluorescence of these molecules with changing vibrational energy E _vib content. On the basis of experimental data and model calculations it has been concluded that at the laser radiation densities used in the case of IR MPE the molecules reach energies considerably exceeding the energies of the electronic levels. It is shown that a nonadiabatic connection between the electronic states leads to the population of mixed electronic states isoenergetic to the vibrational levels of the ground electronic state and to emission of delayed luminescence spectrally identical to the normal luminescence of these molecules. It has been found that when high vibrational levels are populated, new relaxation channels, such as reverse electron relaxation, emission from high vibrational levels of the ground electronic state, and multiquantum vibrational energy transfer at collisions leading to a rapid establishment of vibrational equilibrium become important.     

Dimensional Crossover of Magnetic Transition in Diluted Ising Spin Nets Probed by Muon Spin Relaxation

The magnetic ordering process of Ising spins on diluted square lattice was studied by muon spin relaxation using model compounds Rb₂Co _c Mg_1−c F₄. Muon relaxation shows an anomaly at a remarkably higher temperature T _N ^μSR than the transition temperature determined by neutron Bragg scattering T _N ^ND near the percolation threshold for square lattice (c _p=0.593). The difference between the two temperatures amounts to 50% of T _N ^ND just above c _p. The field cooling effect of DC magnetic susceptibility is appreciable below T _N ^ND while the temperature of the anomaly in AC susceptibility approaches to T _N ^μSR as the frequency is increased. It was concluded that there is a crossover from two-dimensional ordering at T _N ^μSR to three-dimensional ordering at T _N ^ND but the two-dimensional order between T _N ^μSR and T _N ^ND has slow fluctuations due to the fractal structure with a plenty of weak links. This revised version was published online in September 2006 with corrections to the Cover Date.     

Ultrafast Quantum Relaxation Dynamics of Magnetically Ordered Systems with Spin Crossover in an Excited State under a Sudden Perturbation

JETP Letters - A theoretical model based on the relaxation equation for the density matrix has been proposed to describe the ultrafast time dynamics of magnetically ordered systems with spin...     

Nuclear Spin Relaxation in Some Non-viscous Media Using the 181Hf Probe

Perturbed angular correlation (PAC) studies have been performed in liquid mercury, HCl media of different acid strengths, H₂O and H₃PO₄ using a ¹⁸¹Hf probe. It is found that, in case of H₂O, interaction between the nucleus and its excited atom following the β⁻ decay of ¹⁸¹Hf is a possible mechanism for the nuclear spin relaxation in this environment. In the liquid mercury and different acid media, however, the perturbations are found to arise due to molecular fluctuations.     

奇奇核168Lu高自旋态及三轴超形变带的研究

采用TRS方法对¹⁶⁸Lu新发现的4条转动带进行了理论计算,证实了在实验上观测到的一条三轴超形变带,并得到其形变参数值.本工作还对准粒子能量随角频率的变化进行了研究,对实验结果给出了合理解释,说明了为什么实验上很难找到第四条转动带的旋称伙伴带     

Effect of Quantum Point Contact Measurement on Electron Spin State in Quantum Dots

We study the time evolution of two electron spin states in a double quantum-dot system, which includes a nearby quantum point contact （QPC） as a measurement device. We find that the QPC measurement induced decoherence is in the microsecond timescale. We also find that the enhanced QPC measurement will trap the system in its initial spin states, which is consistent with the quantum Zeno effect.     

(110)-GaAs量子阱中光生载流子对电子自旋弛豫的影响

我们实验研究了(110)-GaAs量子阱中光生载流子对电子自旋弛豫的影响。通过测量量子阱的荧光寿命和光学吸收计算,我们能得到不同泵浦光功率下的带间吸收所产生的空穴浓度;相对应地,通过双色磁光科尔旋转技术,我们测量了该GaAs量子阱中电子自旋的动力学过程。结合两者,我们得到了电子自旋弛豫速率与空穴浓度的关系。实验结果表明电子自旋弛豫速率与空穴浓度呈线性依赖关系,验证了BirAronov-Pikus机制主导该体系的电子自旋弛豫。     

Dynamical Correlations in the Ground State: Transitions between One-Phonon Nuclear States

JETP Letters - The probabilities of the E1 transition between the first $${{2}^{ + }}$$ and $${{3}^{ - }}$$ excited levels in nuclei with pairing have been calculated within the self-consistent...