In-plane Component Of Magnetic Field Research Articles

In-plane magnetic field dependence of electric field-induced magnetization switching

Electric field-induced magnetization switching through magnetization precession is investigated as a function of in-plane component of external magnetic field for a CoFeB/MgO-based magnetic tunnel junction with perpendicular easy axis. The switching probability is an oscillatory function of the duration of voltage pulses and its magnitude and period depend on the magnitude of in-plane magnetic field. Experimental results are compared with simulated ones by using Landau-Lifshitz-Gilbert-Langevin equation, and possible factors determining the probability are discussed.

Nonlinear vortex dynamics in an inhomogeneous magnetized plasma with a sheared velocity field

The long term evolution of a vortex chain generated by the nonlinear development of the Kelvin–Helmholtz instability in a magnetized two-fluid plasma with a sheared velocity field is investigated in a two-dimensional configuration. The different roles played by the in-plane magnetic field component and by the density inhomogeneity are elucidated. This investigation is of interest in understanding the plasma dynamics that arises from the nonlinear competition of different plasma instabilities involving the interplay of large and small spatial scales and, in particular, for understanding the mixing mechanism between the solar wind and the Earth's magnetospheric plasmas that occurs at the Earth's magnetospheric flanks.

Locking and unlocking of the counterflow transport inν=1quantum Hall bilayers by tilting of magnetic field

The counterflow transport in quantum Hall bilayers provided by superfluid excitons is locked at small input currents due to a complete leakage caused by the interlayer tunneling. We show that the counterflow critical current I_c^{CF} above which the system unlocks for the counterflow transport can be controlled by a tilt of magnetic field in the plane perpendicular to the current direction. The effect is asymmetric with respect to the tilting angle. The unlocking is accompanied by switching of the systems from the d.c. to the a.c. Josephson state. Similar switching takes place for the tunneling set-up when the current flowing through the system exceeds the critical value I_c^T. At zero tilt the relation between the tunnel and counterflow critical currents is I_c^T=2 I_c^{CF}. We compare the influence of the in-plane magnetic field component B_\parallel on the critical currents I_c^{CF} and I_c^T. The in-plane magnetic field reduces the tunnel critical current and this reduction is symmetric with respect to the tilting angle. It is shown that the difference between I_c^{CF} and I_c^T is essential at field |B_\parallel|\lesssim \phi_0/d \lambda_J, where \phi_0 is the flux quantum, d is the interlayer distance, and \lambda_J is the Josephson length. At larger B_\parallel the critical currents I_c^{CF} and I_c^T almost coincide each other.

Optical out-of-plane spin polarization and charge conductivities in spin-orbit-coupled systems in the presence of an in-plane magnetic field

Out-of-plane spin and charge responses to the terahertz field for a clean two-dimensional electron gas with a Rashba spin-orbit interaction in the presence of an in-plane magnetic field are studied. We show that the characteristic optical spectral behavior is remarkably different from that of the system in the absence of in-plane magnetic fields. It is found that the optical spin polarization normal to the plane is nonzero even for this clean system, in sharp contrast to the static case. Due to the combined effect of spin-orbit coupling and in-plane magnetic field, both diagonal and off-diagonal components of optical charge conductivity tensor are nonvanishing. It is indicated that one can control the spin polarization and the optical current by adjusting the optical frequency. In addition, the out-of-plane spin polarization and conductivities strongly rely on the direction of the external magnetic field. Nevertheless, they meet different angle-dependent relations. This dynamical out-of-plane spin polarization could be measured by the time-resolved Kerr rotation technique.

Collisionless Kelvin-Helmholtz instability and vortex-induced reconnection in the external region of the Earth magnetotail

In a magnetized plasma streaming with a non uniform velocity, the Kelvin-Helmholtz instability plays a major role in mixing different plasma regions and in stretching the magnetic field lines leading to the formation of layers with a sheared magnetic field where magnetic field line reconnection can take place. A relevant example is provided by the formation of a mixing layer between the Earth's magnetosphere and the solar wind at low latitudes during northward periods. In the considered configuration, in the presence of a magnetic field nearly perpendicular to the plane defined by the velocity field and its inhomogeneity direction, velocity shear drives a Kelvin-Helmholtz instability which advects and distorts the magnetic field configuration. If the Alfvén velocity associated to the in-plane magnetic field is sufficiently weak with respect to the variation of the fluid velocity in the plasma, the Kelvin-Helmholtz instability generates fully rolled-up vortices which advect the magnetic field lines into a complex configuration, causing the formation of current layers along the inversion curves of the in-plane magnetic field component. Pairing of the vortices generated by the Kelvin-Helmholtz instability is a well know phenomenon in two-dimensional hydrodynamics. Here we investigate the development of magnetic reconnection during the vortex pairing process and show that completely different magnetic structures are produced depending on how fast the reconnection process develops on the time scale set by the pairing process.

Spin filtering in single magnetic barrier structures revisited

We reexamine spin-dependent transport properties of two-dimensional electrons modulated by the stray field of a ferromagnetic metal (FM) stripe on top. When the magnetization is along the transport direction of the electrons, the FM stripe generates not only a magnetic barrier but also an in-plane magnetic field component. Previous studies have omitted the in-plane magnetic field component and shown that such a device does not possess any spin-filtering effect. We show that with inclusion of this in-plane magnetic field component, a spin polarization of nearly 100% can be achieved in such a single FM-stripe modulated two-dimensional electron gas device.

Effect of toroidal moment on a macroscopic self-organization of electrons in the quantum Hall regime

We have studied CR lineshape of terahertz-light-induced current in InAs quantum wells in tilted quantizing magnetic fields. We have observed dramatic modification of the lineshape with increasing of in-plane component of magnetic field as well as with increasing of transverse built-in electric field in the well. Scenario of the modification shows that the energy spectrum asymmetry is determined by so-called toroidal moment of the system and is a function of Landau quantum number. Macroscopic self-organization of electrons under the conditions of quantum Hall effect has also been directly demonstrated in both linear and saturation regimes of the light absorption.

Anisotropic mean-square displacements in two-dimensional colloidal crystals of tilted dipoles

Superparamagnetic colloidal particles confined to a flat horizontal air-water interface in an external magnetic field, which is tilted relative to the interface, form anisotropic two-dimensional crystals resulting from their mutual dipole-dipole interactions. Using real-space experiments and harmonic lattice theory we explore the mean-square displacements of the particles in the directions parallel and perpendicular to the in-plane component of the external magnetic field as a function of the tilt angle. We find that the anisotropy of the mean-square displacement behaves nonmonotonically as a function of the tilt angle and does not correlate with the structural anisotropy of the crystal.

Disordered quantum Hall ferromagnets and cooperative transport anisotropy

We discuss the behaviour of a quantum Hall system when two Landau levels with opposite spin and combined filling factor near unity are brought into energetic coincidence using an in-plane component of magnetic field. We focus on the interpretation of recent experiments under these conditions (Phys. Rev. Lett. 86 (2001) 866; Phys. Rev. B 64 (2001) 121305), in which a large resistance anisotropy develops at low temperatures. Modelling the systems involved as Ising quantum Hall ferromagnets, we suggest that this transport anisotropy reflects domain formation induced by a random field arising from isotropic sample surface roughness.

Insulating states of a broken-gap two-dimensional electron-hole system

It has recently been found that an InAs/GaSb based electron-hole system exhibits insulating behavior with unusual properties when the numbers of occupied electron and hole Landau levels are equal [R. J. Nicholas, K. Takashina, M. Lakrimi, B. Kardynal, S. Khym, N. J. Mason, D. M. Symons, D. K. Maude, and J. C. Portal, Phys. Rev. Lett. 85, 2364 (2000)]. In this insulating state, the Hall resistance becomes symmetric (even) under field reversal $[{R}_{\mathrm{xy}}{(B)=R}_{\mathrm{xy}}(\ensuremath{-}B)],$ and both the Hall and longitudinal resistances display reproducible fluctuations. In this paper we present experimental studies of the geometry dependence of this phenomenon. In particular, we show conclusively that the conduction responsible for the reproducible fluctuations and the symmetric Hall resistance occur due to the presence of the mesa edge. Further investigations of the edge conductance are presented. We show that as a function of magnetic field, the edge conduction shows a qualitatively opposite behavior to the conductivity in the sample interior. This is confirmed through measurements with an in-plane component of magnetic field. Also, the size of the conductance fluctuations is found to have a monotonic relationship with the absolute value of the conductance. A model based on counterpropagating edge channels is presented which qualitatively accounts for the observed behavior.

Quantum Hall effect in back-gated InAs/GaSb heterostructures under a tilted magnetic field

We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron–hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the extended states of the original electron and hole LLs make the QHE regions along integer- ν net discontinuous. Under tilted magnetic fields, these R xx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron–hole hybridization and the formation of minigaps at LL crossings.

Suppression of surface barriers in single crystals of Bi2Sr2CaCu2O8+δ by in-plane magnetic fields

The non-linear behavior of the in-plane resistivity in the vortex-liquid phase is observed in Bi2Sr2CaCu2O8+δ single crystals, in magnetic fields applied along the c-axis, for samples which favor surface barriers. However, in tilted magnetic fields, it was found that the in-plane magnetic field component strongly suppresses the non-Ohmic behavior of resistivity, which may indicate the suppression of the surface barrier effect.

Quantum Hall ferromagnets, cooperative transport anisotropy, and the random field Ising model

We discuss the behaviour of a quantum Hall system when two Landau levels with opposite spin and combined filling factor near unity are brought into energetic coincidence using an in-plane component of magnetic field. We focus on the interpretation of recent experiments under these conditions [Zeitler et al, Phys. Rev. Lett. 86, 866 (2001); Pan et al, Phys. Rev. B 64, 121305 (2001)], in which a large resistance anisotropy develops at low temperatures. Modelling the systems involved as Ising quantum Hall ferromagnets, we suggest that this transport anisotropy reflects domain formation induced by a random field arising from isotropic sample surface roughness.

Josephson Vortex Qubit: Design, Preparation and Read-Out

junction is discussed in detail. The vortex potential is formed due to its interaction with an inplane magnetic field and a bias current applied to the junction. The profile of the potential is calculated using a standard perturbation approach. We examine the dependence of the potential properties on the junction shape and its electrical parameters and discuss the requirements for observing quantum effects in this system. We have developed and experimentally tested methods for the preparation and read-out of vortex states of this qubit in the classical regime. 1. Introduction In the past years several types of different superconducting circuits [1–6] based on small Josephson junctions in the phase or charge regime have been shown to achieve parameters which are favorable for quantum computation. In Ref. [7], a qubit based on the motion of a Josephson vortex in a long Josephson junction was proposed. A major difference from the small Josephson junction qubit proposals where the effective potential is created by the Josephson or charging energy, is that in the vortex qubit the potential is formed by the magnetic interaction of the vortex magnetic moment with an external magnetic field, as described in Ref. [8]. In heart-shaped annular junctions two classically stable vortex states can be arranged, corresponding to two minima of the potential. While the external field is always applied in the plane of the long junction, its angle Q and strength h can be varied. The bias current across the junction can be used to tilt the potential. These parameters allow to manipulate and control the potential and to read out the qubit state using a zero-voltage critical current measurement. The scheme of readout and preparation of the state for this type of qubit was already demonstrated in the classical regime as briefly described in Ref. [9]. This paper describes details of the calculations necessary to determine the parameter range for the quantum regime, as well as details on the calculation of the effective potential for the vortex. An explanation of the implementation of the elementary single-bit quantum gates using the two in-plane magnetic field components is given. For the calculation of the potential a single-vortex perturbation theory approach [10] is used. Tunneling rates in the quantum regime are determined by numerical diagonalization of the Hamiltonian and compared to a WKB calculation.

Development of a specimen holder for in situ generation of pure in-plane magnetic fields in a transmission electron microscope

As the development of quantised storage media progresses, detailed knowledge is required about the magnetisation reversal behaviour of sub-micron sized magnetic structures in external magnetic fields. Using the Lorentz mode of transmission electron microscopy (LTEM) the magnetic microstructure of thin film samples can be imaged with high spatial resolution. A novel approach for in situ magnetising experiments is described which combines the development of a custom-made sample holder which generates two orthogonal in-plane components of magnetic field in the specimen plane with the benefit of computer-controlled variation of the field. We present a specimen stage suitable for a Philips CM30 Twin/LTEM, which allows the generation of well-defined magnetic in-plane fields in the TEM.

Vortex lattice melting transition in oblique magnetic fields in single crystal Bi 2Sr 2CaCu 2O 8+ δ

The vortex dynamics in single crystal of Bi 2Sr 2CaCu 2O 8+ δ was studied in oblique magnetic fields. The sharp drop of the resistance attributed to the first-order vortex lattice melting transition (VLMT) separates the vortex solid and vortex liquid phases in the wide range of magnetic field directions, even at angles very close to the ab-plane. It was observed that VLMT does not scale with the c-axis magnetic field component but is depressed linearly by the in-plane magnetic field in agreement with recent theoretical prediction by Koshelev. Additionally, it was found that VLMT becomes independent of the magnetic field orientation above the certain value H ab ∗ of the in-plane magnetic field component.

Comment on “Two-dimensional spin confinement in strained-layer quantum wells”

For quasi-two-dimensional p channels, second-order corrections of the perturbation theory to the Zeeman splitting of heavy-hole subbands, which originate from the in-plane magnetic-field component, were found to have magnetic-field dependence and an order of magnitude different from those calculated in a previous paper [R.W. Martin et al., Phys. Rev. B 42, 9237 (1990)]. Because of the zero first-order corrections, second-order corrections determine the behavior of energy separations between magnetic levels of low-lying heavy-hole subbands in a tilted magnetic field which is quite different from that of electrons.

Magnetization in a spin valve head mapped by an MFM tip

We have mapped the magnetization distribution in a spin valve head by monitoring its magneto-resistance /spl delta/R, while scanning the sample surface with an MFM tip. We find that conventional tips give enhanced response at two edges of the sensor. In comparison, mapping with horizontally magnetized tips shows no such artifacts. This is because conventional tips produce in-plane magnetic field components in all radial directions, thus the response /spl delta/R does not simply correspond to local magnetization. In contrast, horizontally magnetized tips produce fields along a single direction. Therefore, mapping of /spl delta/R renders the approximately single-domain magnetization in our spin valve films.

Structure of Vortex Liquid Phase in IrradiatedBi2Sr2CaCu2O8−δCrystals

The c-axis resistivity in irradiated and in pristine BSCCO(2212) crystals is measured as a function of the in-plane magnetic field component at fixed out-of-plane component B_\perp in the vortex liquid phase at T=67 K. From this data we extract the dependence of the phase difference correlation length inside layers on B_\perp and estimate the average length of pieces of vortex lines confined inside columnar defects as a function of the filling factor f=B_\perp / B_\phi. The maximum length, about 15 interlayer distances, is reached near f=0.35.

Spin-reversed quasielectron excitations in the -filling fractional-quantum-Hall-effect state

We report on the effect of an in-plane magnetic field component on the magnetoresistance of the two-dimensional electron system (2DES) and capacitance between the 2DES and gate. The appearance of the \ensuremath{\nu}=1/3 and \ensuremath{\nu}=2/3 fractional-quantum-Hall-effect (FQHE) states has been observed to modify the effect at \ensuremath{\nu}\ensuremath{\gtrsim}2/3. Our results imply the existence of the spin-reversed quasielectron excitations in the \ensuremath{\nu}=2/3 FQHE. Charged excitations with large numbers of reversed spins (skyrmions) recently predicted for the \ensuremath{\nu}=1/3 FQHE state have not been found.