Optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis

A model of an optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis is presented. Different coordinate frames for nuclear spin polarization vector are introduced, and theoretical calculation is conducted to analyze this model. We demonstrate that when the optical pumping nuclear magnetic resonance system rotates in a plane parallel to the quantization axis, it will maintain a steady state with respect to the quantization axis which is independent of rotational speed and direction.

An improved initial rotor position estimation method using high-frequency pulsating voltage injection for PMSM

High frequency pulsating voltage injection method is a good candidate for detecting the initial rotor position of permanent magnet synchronous motor.However,traditional methods require a large number of filters,which leads to the deterioration of system stability and dynamic performance.In order to solve these problems,a new signal demodulation method is proposed in this paper.The proposed new method can directly obtain the amplitude of high-frequency current,thus eliminating the use of filters,improving system stability and dynamic performance and saving the work of adjusting filter parameters.In addition,a new magnetic polarity detection method is proposed,which is robust to current measurement noise.Finally,experiments verify the effectiveness of the method.

Milestones in the Observations of Cosmic Magnetic Fields

Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from analysis of rotation measures of extragalactic radio sources and pulsars, which can be used to construct the 3-D magnetic field structure in the Galactic halo and Galactic disk. Radio synchrotron spurs in the Galactic center show a poloidal field, and the polarization mapping of dust emission and Zeeman observation in the central molecular zone reveal a toroidal magnetic field parallel to the Galactic plane. For nearby galaxies, both optical polarization and multifrequency radio polarization data clearly show the large-scale magnetic field following the spiral arms or dust lanes. For more distant objects, radio polarization is the only approach available to show the magnetic fields in the jets or lobes of radio galaxies or quasars. Clusters of galaxies also contain widely distributed magnetic fields, which are reflected by radio halos or the RM distribution of background objects. The intergalactic space could have been magnetized by outflows or galactic superwinds even in the early universe. The Zeeman effect and polarization of sub-mm and mm emission can be used for the study of magnetic fields in some Galactic molecular clouds but it is observed only at high intensity. Both approaches together can clearly show the role that magnetic fields play in star formation and cloud structure, which in principle would be analogous to galaxy formation from protogalactic clouds. The origin of the cosmic magnetic fields is an active field of research. A primordial magnetic field has not been as yet directly detected, but itsexistence must be considered to give the seed field necessary for many amplification processes that have been developed. Possibly, the magnetic fields were generated in protogalactic plasma clouds by the dynamo process, and maintained again by the dynamo after galaxies were formed.

Vector Magnetic Field Measurement of NOAA AR 10197

A set of two-dimensional Stokes spectral data of NOAA AR 10197 obtained by the Solar Stokes Spectral Telescope （S^3T） at the Yunnan Observatory are quafitatively analyzed. The three components of the vector magnetic field, the strength H, inclination 7 and azimuth X, are derived. Based on the three components, we contour the distributions of the longitudinal magnetic field and transverse magnetic field. The active region （AR） has two different magnetic polarities apparent in the longitudinal magnetic map due to projection effect. There is a basic agreement on the longitudinal magnetic fields between the S^3T and SOHO/MDI magnetograms, with a correlation coefficient PBl = 0.911. The transverse magnetic field of the AR has a radial distribution from a center located in the southwest of the AR. It is also found that the transverse magnetic fields obtained by Huairou Solar Observing Station （HRSOS） have a similar radial distribution. The distributions of transverse magnetic field obtained by S^3T and HRSOS have correlation coefficients, PAzimu = 0.86 and PBt =0.883, in regard to the azimuthal angle and intensity.

Domain wall dynamics driven by a circularly polarized magnetic field in ferrimagnet:effect of Dzyaloshinskii-Moriya interaction

In this work,we study the domain wall motion in ferrimagnet driven by a circularly polarized magnetic field using the collective coordinate theory and atomistic micromagnetic simulations,and we pay particular attention to the effect of Dzyaloshinskii-Moriya interaction(DMI).Similar to the case of antiferromagnetic domain wall,ferrimagnetic wall moves at a speed which is linearly dependent on the DMI magnitude.In addition,it is revealed that the DMI plays a role in modulating the domain wall dynamics similar to that of the net spin density,which suggests another internal parameter for controlling domain wall in ferrimagnets.Moreover,the results show that the domain wall dynamics in ferrimagnets is much faster than that in ferromagnets,which confirms again the great potential of ferrimagnets in future spintronic applications.

Micro Manipulation Using Magnetic Microrobots

When developing microscale robotic systems it is desired that they are capable of performing microscale tasks such as small scale manipulation and transport. In this paper, we demonstrate the transport of microscale objects using single or multiple microrobots in low Reynolds number fluidic environment. The microrobot is composed of a ‘U＇ shaped SU-8 body, coated on one side with nickel. Once the nickel coating is magnetized, the motion of the microrobots can be driven by external magnetic fields. To invoke different responses from two microrobots under a global magnetic field, two batches of microrobots were fabricated with different thicknesses of nickel coating as a way to promote heterogeneity within the microrobot population. The heterogeneity in magnetic content induces different spatial and temporal responses under the same control input, resulting in differences in movement speed. The nickel coated microstructure is manually controlled through a user interface developed using C＋＋. This paper presents a control strategy to navigate the microrobots by controlling the direction and strength of ex- ternally applied magnetic field, as well as orientation of the microrobots based on their polarity. In addition, multiple micro- robots are used to perform transport tasks.

Magnetic polarization of a Mn-doped semiconductor nanostructure controlled by an external bias

The interplay between the electric and magnetic properties in a double quantum well heterostructure doped by magnetic ions is theoretically investigated. In this material, the magnetism is mediated by the hole gas. The total magnetic polarization of the system is controllable by an external applied bias. The device has two equilibrium states （symmetric and antisymmetric configurations）. In the stable configuration （anti-ferromagnetic type）, the particle spin distribution is reversed in the adjacent wells. The stability of the system is investigated by simulating the interaction of the hole gas with the light. By using an ab initio method, we estimate the switching time of the device.

Magnetic field effects in organic light-emitting diodes with Co electrode

Tris-（8-hydroxyquinoline）-aluminum eAlq3T–based organic light-emitting diodes with Co electrode are fabricated. The positive magnetic electroluminescence（MEL） and magnetic conductance（MC） are observed in the samples, reaching 4.35% and 1.67% under the field of 42 m T at 50 K, respectively, and the MEL and MC traces can be fitted to non-Lorentzian line shapes. The MEL varies as a function of the Co thickness and reaches the optimal value at 10 nm. The MEL and MC dependence on voltage and temperature is also investigated. The electron-hole pair model and the spin-polarized injection mechanism are used to understand the experimental results.

Magnetooptics of non-Kramers Eu^(3+) ions in garnets:analysis complemented by crystal-field splitting modeling calculations

Spectra of absorption, luminescence, magnetic circular dichroism （MCD）, and magnetic circular polarization of lumines- cence （MCPL） in Gd3Ga5O12：Eu3＋ and Eu3Ga3O12 garnets were studied within the visible spectral range at 300 K. Analysis of the spectral and temperature dependences of the magnetooptical and optical spectra made it possible to identify the magneto-dipole （MD） and electro-dipole （ED） 4f→4f transitions occurring between Stark sublevels of the 7FJ （J=1, 2） and 5D0 multiplets in Eua＋-containing garnet structures. Quantum mechanical ＂mixing＂ had significant influence on quasi-degenerate states of the non-Kramers rare-earth Eu3＋ ion for Eu3GasOl2 in MCD due to forbidden MD transition 7F1→SD0 and for GdaGasOiE：EU3＋ in MCPL due to MD 4f→4f transition 5Do→7F1 and forced ED-transition 5Do→7F2. A parameterized Hamiltonian defined to operate within the entire 4f（6） ground electronic configuration of Eu3＋ ion was used to model the experimental Stark levels, including their irreducible rep- resentations and wavefunctions. The crystal-field parameters were determined through a Monte-Carlo method in which nine in- dependent crystal-field parameters, Bkq, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental levels was 0.73 meV.

Specific features of Eu^(3+) and Tb^(3+) magnetooptics in gadolinium-gallium garnet (Gd_3Ga_5O_(12))

We reported magnetooptical properties of Eu3＋（4f（6）） and Tb3＋（4f（8）） in single crystals of Gd3Ga5O12 （GGG）, Y3Ga5O12 （YGG）, and Eu3＋（4f（6）） in Eu3Ga5O12 （EuGG） for both ions occupying sites of D2 symmetry in the garnet structure. Absorption, luminescence, and magnetic circular polarization of luminescence （MCPL） spectra of Tb3＋ in GGG and YGG and absorption and magnetic circular dichroism （MCD） of Eu3＋ in EuGG were studied. The data were obtained at 85 K and room temperature （RT）. Magnetic susceptibility of Eu3＋ in EuGG was also measured between 85 K and RT. The magnetooptical and magnetic susceptibility data were modeled using the wavefunctions of the crystal-field split energy （Stark） levels of Eu3＋ and Tb3＋ occupying D2 sites in the same garnets. The results reported gave a precise determination of these Stark level assignments and confirmed the symmetry labels （irreducible representations） of the closely-spaced Stark levels （quasi-doublets） found in the 5D1 （Eu3＋） and 5D4 （Tb3＋） multiplets. Ultraviolet （UV） excitation （300 nm） of the 6PJ and 6IJ states of Gd3＋ in the doped GGG crystals led to emission from 5D4 （Tb3＋） and 5D1 and 5D0 （Eu3＋） through radiationless energy transfer to the 4f（n–1）5d band of Tb3＋ and to UV quintet states of Eu3＋. The temperature-dependent emission line shapes and line shifts of the magnetooptical transitions excited by UV radiation suggested a novel way to explore energy transfer mechanisms in this rare-earth doped garnet system.