A nuclear-spin based rotation sensor using optical polarization and detection methods

We describe a rotation sensor that is based on the detection of the nuclear magnetic resonance signal of¹²⁹Xe in the gas phase. Under rotation shifts of the signal phase and Larmor frequency occur, which can be used to determine orientational angle variations with an accuracy of about 1^o and rotation rates of 0.4 mHz to 5 Hz with a precision of 0.4 mHz during the measurement time, which is of the order of 3×T ₂, the nuclear spin relaxation time. The nuclear spin species is polarized by spin-exchange collisions with optically pumped ground-state spins of Rb-gas atoms. The Rb atoms also present in the sample are used as a magnetometer to probe the free-induction decay of the nuclear spin ensemble. Polarization, detection, and data processing sheemes are described in detail and the current sensitivity and limitations of this Stuttgart nuclear magnetic resonance (NMR) gyroscope are discussed. Possibilities for further improvements are pointed out.     

Spin-rotating magnet for the ΔσL(np) experiment at LHEP JINR

The spin rotating magnet (SRM) is purposed for the orientation rotation of the nucleon spins in the polarized beam from the transverse (T) direction with respect to the nucleon beam momentum to the longitudinal (L) one. The longitudinally polarized neutron beam was used in the experiment for measuring the total cross section difference Δσ_L(np) with parallel and antiparallel orientation of the participant L polarization. To perform the nucleon spin rotation in the polarized nucleon beam through the angle of 90° over the beam momentum region of ～1.8–5.5 GeV/c, a proper spin rotation device had to be prepared. For this purpose, the necessary calculations of corresponding values of the magnetic induction integral were carried out. Using the calculations the dipole magnet SP 57 type was chosen for the Δσ_L(np) experiment and the required reconstruction of its pole tips was also accomplished. After the SRM installation at the neutron beam line the appropriate apparatus set for the magnetic measurements was prepared and the precise measurements of the whole set of the SRM characteristics were performed. The obtained results for the SRM magnetic field parameters were successfully used during the Δσ_L(np) experimental runs to specify the current at this magnet coil corresponding to the calculated magnetic induction integral for the given neutron beam momentum.     

Spin waves on chains of YIG particles: dispersion relations,Faraday rotation,and power transmission

We calculate the dispersion relations for spin waves on a periodic chain of spherical or cylindrical Yttrium Iron Garnet (YIG) particles. We use the quasistatic approximation, appropriate when kd ? 1, where k is the wave number and d the interparticle spacing. In this regime, because of the magnetic dipole-dipole interaction between the localized magnetic excitations on neighboring particles, dispersive spin waves can propagate along the chain. The waves are analogous to plasmonic waves generated by electric dipole-dipole interactions between plasmons on neighboring metallic particles. The spin waves can be longitudinal (L), transverse (T), or elliptically polarized. We find that a linearly polarized spin wave undergoes a Faraday rotation as it propagates along the chain. The amount of Faraday rotation can be tuned by varying the off-diagonal component of the permeability tensor. We also discuss the possibility of wireless power transmission along the chain using these coupled spin waves.     

磁光克尔效应中的光子自旋分裂

光子自旋霍尔效应类似于电子系统中的电子自旋霍尔效应, 是在折射率梯度和光子分别扮演的外场和自旋电子的角色下, 由自旋-轨道相互作用而产生的光子自旋分裂现象. 光子自旋霍尔效应为操控光子提供了新的途径, 同时也提供了一种精确测量相关物理效应的方法. 本文研究了磁光克尔效应中光子自旋分裂现象, 建立了磁光克尔旋转与光子自旋霍尔效应之间的定量关系, 并通过弱测量系统观测了磁场作用下铁膜表面的光子自旋分裂位移, 得到相应的磁光旋转角, 验证了我们所推导的理论预测. 本文的研究成果为精确测量磁光克尔系数和磁光克尔旋转角提供了一种新方法.     

Effects of impurities and vortices on the low-energy spin excitations in high-Tc materials

We review a theoretical scenario for the origin of the spin-glass phase of underdoped cuprate materials. In particular it is shown how disorder in a correlated d-wave superconductor generates a magnetic phase by inducing local droplets of antiferromagnetic order which eventually merge and form a quasi-long range ordered state. When correlations are sufficiently strong, disorder is unimportant for the generation of static magnetism but plays an additional role of pinning disordered stripe configurations. We calculate the spin excitations in a disordered spin-density wave phase, and show how disorder and/or applied magnetic fields lead to a slowing down of the dynamical spin fluctuations in agreement with neutron scattering and muon spin rotation (μSR) experiments.     

Passage of relativistic magnetic dipole moments through magnetic fields

We have solved the Dirac equation with an anomalous moment Pauli-coupling exactly for a constant magnetic field and derived the general relativistic formulas for phase changes due to translational motion and spin rotations. We also give transmission and reflection coefficients, spin rotation for tunnelling and barrier penetration. For ultrarelativistic particles the spin rotation angle on the path of lengthL is equal to (2μB L/ħc)[1 +m ² c ⁴/(E²-μ ² B ²)].

     

Magnetic structure of low-dimensional LiCu2O2 multiferroic according to 63,65Cu and 7Li NMR studies

The complex NMR study of the magnetic structure of LiCu₂O₂ multiferroic has been performed. It has been shown that the spin spirals in LiCu₂O₂ are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu²⁺ chains. A magnetic field of H ₀ = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H ₀ ?? b.     

Spin-polarization of an electro-static positron beam

We constructed an electro-static positron beam apparatus. We fabricated a simple spin-polarimeter composed of a permanent magnet with a surface magnetic field of 0.65 T and an iron pole piece. The longitudinal spin-polarization of the positron beam was determined to be 0.3 by analyzing the magnetic field dependence of the Doppler broadening of annihilation radiation from a fused silica specimen. The effect of spin rotation was examined using an iron poly-crystal and a simple E × B filter.     

Triangular spin configuration and weak ferromagnetism of Mn3Sn and Mn3Ge

Polarized-neutron diffraction by Mn₃Sn and Mn₃Ge in magnetic field reveals that the spin triangle coincides with the c-plane, is the inversion of the atomic triangle, and rotates opposite to the rotation of the c-plane component of magnetic field. Theory predicts that the inverted spin triangle is free to rotate and the associated weak ferromagnetic moment rotates oppositely.     

Induced neutron magnetic form factor of LaSn3

Polarized neutron scattering techniques have been used to study the spatial distribution of the magnetization induced in a single crystal of LaSn₃ by a magnetic field of 42.5 kG at 100 K. We find that the magnetic form factor decreases very rapidly with increasing scattering angle, and bears no resemblance to the spin or orbital free-atom magnetic form factor. The experimental results are in reasonable agreement with band theoretical calculations of the spin magnetic form factor of LaSn₃. We conclude that (a) the spin part is the dominant contribution to the bulk susceptibility of LaSn₃ and (b) there is a substantial amount of Sn-5p electronic character in the wavefunctions near the Fermi level.     

Die Rotation des Elektronenspins beim ebenen Tunnelprozeß mit überlagertem homogenem Magnetfeld

Measurements of the spin polarization of field emitted electrons from various ferromagnetic (Gd, Ni, Fe) and nonferromagnetic metals (W) show a steady increase of the angle? _s between momentum and electron spin with increasing external magnetic field (spin rotation). This effect is refered to the coupling between the magnetic moment of the electron and the strong electric field in the potential barrier at the emitter surface during the tunneling process. A formal application of the equation of spin motion derived by Bargmann, Michel and Telegdi for an electron moving in homogeneous electromagnetic fields delivers a quantitative agreement with the experimental results.     

Long time effects in the spin glass Cd1−xMnxTe

Long time effects in the spin glass Cd_1-xMn_xTe are investigated by measurements of the low field Faraday rotation effect. Strongly marked fluctuations are observed in the time dependence of the Faraday angle below the critical temperature. That seems to be a new effect in spin glasses.     

The grain size effect on the magnetic properties in NiZn ferrite and the quality factor of the inductor

Polycrystalline ferrite materials with the chemical composition of Ni_0.49Zn_0.49Co_0.02Fe_1.90O_x have been fabricated using the conventional ceramic sintering method. Grain sizes have been adjusted from ∼2.2 to ∼13.5 μm with changing sintering conditions. From the measurements of the complex permeability, it is suggested that the permeability is dominated only by the spin rotation at mono-domain state and both domain wall and spin rotation contribute at multi-domain state. At mono-domain state, the core loss has been drastically decreased similar to the other work. The measurement result for the loss angle indicates that the low loss state can be maintained up to the higher magnetic field with smaller grain size in spite of the mono-domain state. The simplified wire-wounded type inductors have been also fabricated and characterized. The results have shown that the inductor fabricated with the smaller grain size has a better performance in the quality value under relatively higher current.     

3D Larmor clock and barrier interaction times for tunneling

We study a three-dimensional spin dynamics of tunneling particles with spin 1/2 through a barrier in the presence of a static and a small time-dependent magnetic fields, perpendicular to each other. The spin dynamics is adopted as a 3D Larmor clock to derive the traversal and reflection times for tunneling (Büttiker, 1983) [14]. We show that the two times can be determined by a real three-dimensional rotation of spin, without requiring the effective rotation due to probability imbalance, and are directly related to the change of spin along its initial polarization direction. We also discuss the experimental feasibility of the present model.     

Quantum spin liquid in interacting Kane-Mele model with staggered on-site potential

In this paper, we mainly study the magnetic properties of the interacting Kane-Mele model with staggered on-site potential. Due to the absence of spin rotation symmetry, there exists a spin anisotropic energy term in the effective nonlinear σ model (NLσM). Based on the NLσM with spin anisotropic energy term, we derive a complex phase diagram and find that there exist quantum spin liquid states at the moderate coupling region.     

Symmetry and spin dephasing in (110)-grown quantum wells

Symmetry and spin dephasing in (110)-grown GaAs quantum wells (QWs) are investigated applying magnetic field induced photogalvanic effect and time-resolved Kerr rotation. We show that magnetic field induced photogalvanic effect provides a tool to probe the symmetry of (110)-grown quantum wells. The photocurrent is only observed for asymmetric structures but vanishes for symmetric QWs. Applying Kerr rotation we prove that in the latter case the spin relaxation time is maximal; therefore, these structures set the upper limit of spin dephasing in GaAs QWs. We also demonstrate that structure inversion asymmetry can be controllably tuned to zero by variation of delta-doping layer positions.     

Dependence of electron spin g-factor on magnetic field in quantum wells

The dependence of electron spin g-factor on magnetic field has been investigated in GaAs/AlGaAs quantum wells. We have estimated the electron g-factor from spin precession frequency in time-resolved photoluminescence measurements under a magnetic field in different configurations; the magnetic field perpendicular (g_⊥) and parallel (g_∥) to the quantum confinement direction. When the angle between the magnetic field and the confinement direction is 45°, we have found that g-factor varies depending on the direction of magnetic field and the circular polarization type of excitation light (σ⁺ or σ^?). These dependences of g-factor exhibit main features of Overhauser effect that nuclear spins react back on electron spin precession. The value of g_⊥ and g_∥ corrected for the nuclear effects agree well with the results of four-band k·p perturbation calculations.     

Quasiballistic magnetization reversal

We demonstrate a quasiballistic switching of the magnetization in a microscopic magnetoresistive memory cell. By means of time resolved magnetotransport, we follow the large angle precession of the free layer magnetization of a spin valve cell upon application of transverse magnetic field pulses. Stopping the field pulse after a 180 degrees precession rotation leads to magnetization reversal with reversal times as short as 165 ps. This switching mode represents the fundamental ultrafast limit of field induced magnetization reversal.