Possible pairing-induced even-denominator fractional quantum Hall effect in the lowest Landau level

We report on our theoretical investigations that point to the possibility of a fractional quantum Hall effect with partial spin polarization at nu = 3/8. The physics of the incompressible state proposed here involves p-wave pairing of composite fermions in the spin reversed sector. The temperature and magnetic field regimes for the realization of this state are estimated.     

Comparative study of coherent terahertz emission from Fe/Pt ferromagnetic heterostructures

The ultrafast spin dynamic of in-plane magnetized Fe/Pt films was investigated by terahertz emission spectroscopy. The amplitude of the emitted terahertz wave is proportional to the intensity of the exciting laser beams.Both the amplitude and polarity of the terahertz wave can be adjusted by modifying the external magnetic field.The dependency of the amplitude on external magnetic fields is coincident to the hysteresis loops of the sample.Also, the polarity of the terahertz wave is reversed, as the magnetization orientation is reversed. The superdiffusive transient spin current with an inverse spin Hall effect is attributed to the main mechanism of the terahertz emission.     

Spin splitter regime of a mesoscopic Rashba ring

Using the non-equilibrium Greens' function formalism we calculate the spin currents in a one-dimensional ring coupled to three leads and in the presence of perpendicular magnetic flux Φ and Rashba spin-orbit coupling. A finite bias is applied between the input lead and the other two output leads. We show that the spin-orbit coupling allows one to operate this system as a spin splitter, i.e. the output leads deliver spin-polarized currents with different orientations. We find that the spin splitter operation can be tuned at integer multiples of Φ/Φ₀. Its efficiency depends not only on the value of the Rashba coupling but also on the bias applied between the input and output leads. The selected spin orientation of the output leads can be reversed by a slight change of their contact position. We discuss as well the connection between the spin splitter operation and the spectral properties of the ring.     

Interplay between nonequilibrium and equilibrium spin torque using synthetic ferrimagnets

We discuss the current induced magnetization dynamics of spin valves F(0)|N|SyF where the free layer is a synthetic ferrimagnet SyF made of two ferromagnetic layers F(1) and F(2) coupled by RKKY exchange coupling. When the magnetic moment of the outer layer F(2) dominates the magnetization of the SyF, the sign of the effective spin torque exerted on the layer F(1) is controlled by the coupling's strength: for weak coupling the spin torque tends to antialign F(1)'s magnetization with respect to the pinned layer F(0). At large coupling the situation is reversed and tends to align F(1) with respect to F(0). At intermediate coupling, numerical simulations reveal that the competition between these two incompatible limits leads generically to spin torque oscillator (STO) behavior. The STO is found at zero magnetic field, with very significant amplitude of oscillations and frequencies up to 50 GHz or higher.     

Characterizing a high spin magnetic impurity via Andreev reflection spectroscopy

The ground state properties of a high spin magnetic impurity and its interaction with an electronic spin are probed via Andreev reflection. We see that through the charge and spin conductance one can effectively estimate the interaction strength, the ground state spin and magnetic moment of any high spin magnetic impurity. We show how a high spin magnetic impurity at the junction between a normal metal and superconductor can contribute to superconducting spintronics applications. Particularly, while spin conductance is absent below the gap for Ferromagnet-Insulator-Superconductor junctions we show that in the case of a Normal metal-High spin magnetic impurity-Normal Metal-Insulator-Superconductor (NMNIS) junction it is present. Further, it is seen that pure spin conduction can exist without any accompanying charge conduction in the NMNIS junction.     

Optimised adiabatic fast passage spin flipping for He neutron spin filters

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized ³He used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the ³He nuclei the polarization of a neutron beam can be efficiently reversed allowing for the transmission of a neutron beam polarized in either spin state. Using an amplitude modulated frequency sweep lasting 500 ms we can spin flip a polarized ³He neutron spin filter with only 1.8×10⁻⁵ loss in ³He polarization. The small magnetic fields (10-15 G) used to house neutron spin filters mean the ³He resonant frequencies are low enough to be generated using a computer with a digital I/O card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using ³He neutron spin filters and polarization losses can be minimised by adjusting sweep parameters.     

Spin-polarization and x-ray magnetic circular dichroism in GaAs

The combination of angular spin momentum with electronics is a promising successor to charge-based electronics. The conduction bands in GaAs may become spin-polarized via optical spin pumping, doping with magnetic ions, or induction of a moment with an external magnetic field. We investigated the spin populations in GaAs with x-ray magnetic circular dichroism for each of these three cases. We find strong anti-symmetric lineshapes at the Ga L₃ edge indicating conduction band spin splitting, with differences in line width and amplitude depending on the source of spin polarization.     

Effect of Rashba spin–orbit coupling on the spin polarized transport in diluted magnetic semiconductor barrier structures

We investigate theoretically the effects of Rashba spin–orbit coupling on the spin dependent transport through diluted magnetic semiconductor single and double barrier structures in the presence of a magnetic field. We find that the Rashba spin–orbit coupling gives rise to an enhancement of the negative tunnelling magnetoresistance of the diluted magnetic semiconductor single barrier structure and a pronounced beating pattern in the tunnelling magnetoresistance and spin polarization of the diluted magnetic semiconductor double barrier structure.     

Spin kinetic Monte Carlo method for nanoferromagnetism and magnetization dynamics of nanomagnets with large magnetic anisotropy

The Kinetic Monte Carlo (KMC) method based on the transition-state theory, powerful and famous for simulating atomic epitaxial growth of thin films and nanostructures, was used recently to simulate the nanoferromagnetism and magnetization dynamics of nanomagnets with giant magnetic anisotropy. We present a brief introduction to the KMC method and show how to reformulate it for nanoscale spin systems. Large enough magnetic anisotropy, observed experimentally and shown theoretically in terms of first-principle calculation, is not only essential to stabilize spin orientation but also necessary in making the transition-state barriers during spin reversals for spin KMC simulation. We show two applications of the spin KMC method to monatomic spin chains and spin-polarized-current controlled composite nanomagnets with giant magnetic anisotropy. This spin KMC method can be applied to other anisotropic nanomagnets and composite nanomagnets as long as their magnetic anisotropy energies are large enough.      

Guiding and trapping of electron spin waves in atomic hydrogen gas

We present a high magnetic field study of electron spin waves in atomic hydrogen gas compressed to high densities of ～10(18) cm(-3) at temperatures ranging from 0.26 to 0.6 K. We observed a variety of spin wave modes caused by the identical spin rotation effect with strong dependence on the spatial profile of the polarizing magnetic field. We demonstrate confinement of these modes in regions of strong magnetic field and manipulate their spatial distribution by changing the position of the field maximum.     

High-temperature dynamics of surface magnetism in iron thin films

Finite-temperature magnetic properties of iron thin films are investigated by computer simulation over a broad range of temperatures up to the point of the ferromagnetic–paramagnetic phase transition. The coupled dynamics of atoms and magnetic moments is treated using the large-scale spin–lattice dynamics (SLD) algorithm. We investigate surface and bulk magnetic properties of iron, and how these properties vary as a function of temperature, film thickness and surface crystallography. We find that magnetization at surfaces is enhanced at low temperatures and suppressed at higher temperatures, in agreement with experimental observations. The effective Curie temperature of a film decreases as a function of thickness. Short-range magnetic order and non-vanishing spin–spin spatial correlations are found above the Curie temperature. The spin autocorrelation functions exhibit slower oscillations with longer decoherence times near the surface. We also find that the directional spin disorder has a significant effect on the surface strain.     

Tunable Kondo effect in a double quantum dot coupled to ferromagnetic contacts

We investigate the effects induced by ferromagnetic contacts attached to a serial double quantum dot. Spin polarization generates effective magnetic fields and suppresses the Kondo effect in each dot. The superexchange interaction J(AFM), tuned by the interdot tunneling rate t, can be used to compensate the effective fields and restore the Kondo resonance when the contact polarizations are aligned. As a consequence, the direction of the spin conductance can be controlled and even reversed using electrostatic gates alone. Our results demonstrate a new approach for controlling spin-dependent transport in carbon nanotube double dot devices.     

Large Magnetoresistance Based on Double Spin Filter Tunnel Barriers

We propose and theoretically analyse a double magnetic tunnel device that takes advantages of the spin filter effect. Two magnetic tunnel barriers are formed by different spin filters which have different barrier heights. The magnetoresistance of the device is low （high） when the magnetic moments of the two spin filters are parallel （antiparallel）. We present a theoretical calculation of the magnetoresistance based on electric tunnel effect. In addition, the effect of the difference barrier heights and exchange splitting energies between the two spin filters are also analysed in detail. The numerical results show that the spin filter in this configuration gives a magnetoresistance larger than that with standard magnetic tunnel junctions.     

Kondo screening cloud in a superconductor with mixed s-wave and p-wave pairing states

We study the Kondo screening of a spin-1/2 magnetic impurity coupled to a superconductor, which is fabricated by combination of an s-wave superconductor, a ferromagnet and a semiconductor with Rashba spin—orbit coupling (RSOC). The proximity induced superconducting states include the s-wave and p-wave pairing components with the aids of RSOC, and the ferromagnet induces a Zeeman field which removes the spin degeneracy of the quasiparticles in the triplet states. Thus, the Kondo screening of magnetic impurity involves the orbital degrees of freedom, and is also affected by the Zeeman field. Using the variational method, we calculate the binding energy and the spin—spin correlation between the magnetic impurity and the electrons in the coexisting s-wave and p-wave pairing states. We find that Kondo singlet forms more easily with stronger RSOC, but Zeeman field in general decreases the binding energy. The spin—spin correlation decays fast in the vicinity of the magnetic impurity. Due to the RSOC, the spatial spin—spin correlation becomes highly anisotropic, and the Zeeman field can induce extra asymmetry to the off-diagonal components of the spin—spin correlation. Our study can offer some insights into the studies of extrinsic topological superconductors fabricated from the hybrid structures containing chains of magnetic impurities.     

Development of neutron spin phase contrast imaging

We present an imaging technique utilizing a neutron spin interferometer. Neutron spin phase contrast is achieved in spatial resolved measurements of the phase difference between two superposed neutron spin states introduced by passing through a magnetic sample. Since the phase difference of spin states parallel and anti-parallel to the magnetic field is proportional to the magnetic field integral, it is possible to record images of the internal magnetic field distribution of the sample. Taking advantage of high transmission probabilities, neutron spin phase contrast provides non-destructive images of internal magnetic structures.     

Spin-dependent transport in a nanopillar non-local spin valve

We investigate the injection of a pure spin current into a non-magnetic Cu wire in a lateral spin valve. We detect the spin accumulation occurring at the interfaces between the magnetic nanopillars and the non-magnetic wire in the non-local geometry. We confirm that the accumulated spins diffuse equally in the Cu wire irrespective of the presence of a charge current. The inversion of the injector and detector magnetic nanopillars does not affect the spin signal, in agreement with analytical predictions for this system.     

Spin-polarized current in double quantum dots

We analyze the transport through asymmetric double quantum dots with an inhomogeneous Zeeman splitting in the presence of crossed dc and ac magnetic fields.A strong spin-polarized current can be obtained by changing the dc magnetic field.It is mainly due to the resonant tunnelling.But for the ferromagnetic right electrode,the electron spin resonance also plays an important role in transport.We show that the double quantum dots with three-level mixing under crossed dc and ac magnetic fields can act not only as a bipolar spin filter but also as a spin inverter under suitable conditions.     

Magnetoelectric memory effect in the Y-type hexaferrite BaSrZnMgFe_(12)O_(22)

We report on the magnetic and magnetoelectric properties of the Y-type hexaferrite BaSrZnMgFe_(12)O_(22),which undergoes transitions from a collinear ferrimagnetic phase to a proper screw phase at 310 K and to a longitudinal conical phase at 45 K.Magnetic and electric measurements revealed that the magnetic structure with spiral spin order can be modified by applying a magnetic field,resulting in magnetically controllable electric polarization.It was observed that BaSrZnMgFe_(12)O_(22)exhibits an anomalous magnetoelectric memory effect:the ferroelectric state can be partially recovered from the paraelectric phase with collinear spin structure by reducing magnetic field at 20 K.We ascribe this memory effect to the pinning of multiferroic domain walls,where spin chirality and structure are preserved even in the nonpolar collinear spin state.     

Tuning of exciton states in a magnetic quantum ring

The exciton states in a CdTe quantum ring subjected to an external magnetic field containing a single magnetic impurity are investigated. We have used the multiband approximation which includes the heavy hole–light hole coupling effects. The electron–hole spin interactions and the s, p–d interactions between the electron, the hole and the magnetic impurity are also included. The exciton energy levels and optical transitions are evaluated using the exact diagonalization scheme. We show that due to the spin interactions it is possible to change the bright exciton state into the dark state and vice versa with the help of a magnetic field. We propose a new route to experimentally estimate the s, p–d spin interaction constants.     

Interaction of $F=2$ Spinor Bose Condensate with Driven External Magnetic Fields

We have studied the interaction of $F=2$ spinor Bose condensate with a combination of static and sinusoidal magnetic field $b_l(t)=b_0+b\cos(\omega t)$. We find that the tunneling current among spin 0 and spin $\pm1$, spin 0 and spin $\pm2$, spin $\pm1$ and spin $\pm2$ may exhibit the incremental oscillation behavior, which depends on the field parameters of the reduced amplitudes of the transverse and the longitudinal magnetic fields respectively. This means that the dynamics spin localization can be adjusted experimentally by selecting the less values of the reduced amplitudes of the transverse magnetic field $b_x/\omega$ and those of the longitudinal magnetic field $b/\omega$.