Arbitrary Magnetization Direction Research Articles

Electron-spin filter based on hybrid ferromagnetic and semiconductor nanosystem

We propose a scheme to realize electron-spin filtering based on generic ferromagnetic and semiconductor hybrid nanosystem, which can be experimentally realized by depositing a magnetized ferromagnetic stripe with arbitrary magnetization direction on the surface of a semiconductor heterostructure. It is shown that large spin-polarized current can be achieved in the device, which may provide an alternative scheme to spin-polarize electrons into semiconductors and such a device may be used as an electron-spin filter.

Signatures of retroreflection and induced triplet electron-hole correlations in ferromagnet–s-wave-superconductor structures

We present a theoretical study of a ferromagnet--$s$-wave-superconductor junction to investigate the signatures of induced triplet correlations in the system. We apply the extended Blonder-Tinkham-Klapwijk formalism and allow for an arbitrary magnetization strength and direction of the ferromagnet, a spin-active barrier, Fermi-vector mismatch, and different effective masses in the two systems. It is found that the phase associated with the $xy$ components of the magnetization in the ferromagnet couples with the superconducting phase and induces spin triplet pairing correlations in the superconductor, if the tunneling barrier acts as a spin filter. This feature leads to an induced spin-triplet pairing correlation in the ferromagnet, along with a spin-triplet electron-hole coherence due to an interplay between the ferromagnetic and superconducting phases. As our main result, we investigate the experimental signatures of retrorelection, manifested in the tunneling conductance of a ferromagnet--$s$-wave-superconductor junction with a spin-active interface.

ELECTRON-SPIN FILTERING IN HYBRID FERROMAGNETIC/SEMICONDUCTOR NANOSYSTEM

The spin-dependent transport of electrons in realistic ferromagnetic/semiconductor hybrid nanosystems was investigated theoretically. This kind of nanosystem can be experimentally realized by depositing a magnetized ferromagnetic strip with arbitrary magnetization direction on the surface of a semiconductor heterostructure. It is revealed that a large spin-polarized current can be achieved in such a device. It is also shown that the spin polarity of the electron transport can be switched by adjusting the structural parameters and location of the ferromagntic strip in the system. These interesting properties may provide an alternative scheme to spin-polarized electrons into semiconductors, and such a nanosystem may be used as a spin filter.

Giant magnetoresistance effect in hybrid ferromagnetic/semiconductor nanosystems

We theoretically investigate the giant magnetoresistance (GMR) effect in general magnetically modulated semiconductor nanosystems, which can be realized experimentally by depositing two parallel ferromagnetic strips on the top of a heterostructure. Here the exact magnetic profiles and arbitrary magnetization direction of ferromagnetic strips are emphasized. It is shown that a considerable GMR effect can be achieved in such nanosystems due to the significant transmission difference for electrons tunneling through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio is strongly influenced by the magnetization direction of ferromagnetic strips in nanosystems, thus possibly leading to tunable GMR devices.

Spin-dependent shot noise in ferromagnet/quantum dot/ferromagnet tunneling system

We study the shot noise spectrum of the system composed of a semiconductor quantum dot coupled to two ferromagnetic leads with arbitrary relative magnetization direction. A general formula for the spin-dependent noise spectrum is obtained within the formalism of the nonequilibrium Green functions. We show that the noise spectrum and Fano factor can increase or decrease with the relative angle between the magnetizations of the two leads, which depends on the system parameters. The spin current correlations strongly depend on the spin orientations and show a nonmonotonic behavior versus the relative magnetization angle.

One-electron Green’s function of multilayer magnetic systems

We propose a method for constructing a symmetric one-electron Green’s function of a magnetic multilayer system with an arbitrary direction of homogeneous magnetization of magnetic layers. We show that the constructed Green’s function allows imposing special boundary conditions.

Spin polarization of two-dimensional electron gas in hybrid ferromagnetic/semiconductor nanostructures

We present a theoretical study on the spin-dependent transport of electrons in hybrid ferromagnetic/semiconductor nanosystem under an applied bias voltage. Experimentally, this kind of nanosystem can be realized by depositing a magnetized ferromagnetic stripe with arbitrary magnetization direction on the surface of a semiconductor heterostructure. It is shown that large spin-polarized current can be achieved in such a nanosystem. It is also shown that the spin polarity of the electron transport can be switched by adjusting the applied bias voltage. These interesting properties may provide an alternative scheme to realize spin injection into semiconductors, and such a nanosystem may be used as a tunable spin-filter by bias voltage.

Spin filtering in magnetic/semiconductor hybrid nanostructures

We study theoretically the spin-dependent electron transport in realistic magnetic-barrier nanostructures, which can be experimentally realized by depositing a magnetized ferromagnetic stripe with arbitrary magnetization direction on the surface of a semiconductor heterostructure. It is shown that highly spin-polarized current can be achieved in this kind of nanostructures. It is also shown that the spin polarity of the electron transport can be switched by adjusting the magnetized angle of the ferromagnetic stripe in the system. These interesting properties may provide an alternative scheme to spin-polarize electrons into semiconductors and may be used as a spin-filter.

Spin drift, spin precession, and magnetoresistance of noncollinear magnet-polymer-magnet structures

We present a theory to describe spin transport across a polymer sandwiched between magnetic contacts with arbitrary magnetization directions. We find that even a weak magnetic field can significantly modify spin transport in polymers through spin precession. It is shown that the interplay of spin drift (due to electric field) and spin precession can lead to damped oscillating magnetoresistance as the magnetic field increases. Our theory is used to explain the recently observed magnetoresistance and $I\text{\penalty1000-\hskip0pt}V$ characteristics in such organic structures. Potential device applications are discussed.

Readback Responses for Complex Recording Media Configurations

This paper describes a relatively simple approach to calculating the frequency response for a two-dimensional (2-D) magnetic recording system with a medium that can include an arbitrary number of layers. Each layer may have an arbitrary magnetization direction, anisotropic permeability, and exchange coupling. The approach relies on an initial transformation into the spatial frequency domain and then the use of transmission matrices to relate the fields in the different layers. The approach is general in that it provides a method for finding the field configuration for any set of 2-D magnetic sources embedded in a layered magnetic medium with a linear B--H relationship. Here, we focus on calculating the readback response for a variety of longitudinal and perpendicular recording configurations. Since the permeability may have any wavelength dependence, we can easily include the effect of exchange coupling in the underlayer.

The construction of the Green functions for GMR structures of complex geometry

We constructed the one-particle Green functions for two systems exhibiting giant magnetoresistance. The first one is a multilayer with arbitrary magnetization directions of the ferromagnetic layers, exchange splitting of the conducting electron band and intrinsic potential. The second one is a segmented nanowire with spin-dependent electron scattering at the lateral interfaces.

Simplified analytic formulae for magneto-optical Kerr effects in ultrathin magnetic films

Expressions are presented for various magneto-optical Kerr effects in the ultrathin film limit with arbitrary magnetization direction by considering the multiple reflections within an optically thin film. The Kerr effect of p- and s-polarization consists of products of two factors: the prefactor, dependent only on the optical parameters of the system, and the main factor of the polar Kerr effect for normal incidence in the ultrathin limit.

Generalized analytic formulae for magneto-optical Kerr effects

We have developed simplified analytic expressions for magneto-optical Kerr effects of both optically thick and ultrathin films in the general case, where a magnetic medium had an arbitrary direction of magnetization and a beam of light was obliquely incident to the medium. It was found that the simplified analytic formulae for the Kerr effects of p and s waves consisted of a product of two factors for both optically thick and ultrathin films: the prefactor dependent only on the optical parameters of the system and the main factor of the polar Kerr effect for a normal incidence case. We have also derived some useful relations among the Kerr effects in the polar and longitudinal configurations. We have demonstrated that the theoretical calculations using the present analytic formulae could well match the experimental polar and longitudinal Kerr rotation angles of magnetic films measured with varying incident angles.

Effect of surface spin pinning on the spin-wave propagation in yttrium iron garnet films

The effect of the surface spin pinning on the spin-wave dispersion and propagation characteristics of yttrium iron garnet (YIG) film was studied both experimentally and theoretically. Modification of the spin-wave amplitude frequency response due to the variations of the pinning conditions on the film surfaces and the bias magnetization direction was studied. Ion bombardment with low-energy H/sup +/ ions was used to control the surface spins pinning. Strong attenuation notches in the spin-wave amplitude-frequency response of ion processed YIG film was treated in terms of dipole hybridization of dispersion branches and appearance of the dipole "gaps" in spin-wave spectrum. The hybridization of spin-wave spectrum was studied for the case of arbitrary magnetization direction and arbitrary surface spin pinning. It has been found that for noninfinite pinning of surface spins, there are magnetization directions for which the gaps in the spectrum are smaller than relaxation frequency, and spin-wave response is smooth.

Derivation of simplified analytic formulae for magneto-optical Kerr effects

We have derived simplified analytic expressions for various magneto-optical Kerr effects of an optically thick medium having an arbitrary magnetization direction. We have found that the simplified formulae for the Kerr effects of p and s waves consisted of a product of two factors: the prefactor dependent pure optical parameters of the system and the main factor of the polar Kerr effect for a normal incidence case. The measured magneto-optic polar Kerr rotation angles of Co/Pd multilayers and the longitudinal Kerr rotation angles of Cu/Co multilayers with varying incident angles could be well fitted using the simplified analytical formulae.

Spin wave modes in inhomogeneous ferromagnetic film at arbitrary magnetic field direction

A generalization of the Portis model for the case of arbitrary direction of magnetization is presented, which gives the separation of linear positioned modes decreasing with θ as δ(H)(θ)/δH(0) = [12(3 cos2θ − 1)]12 till θ ≥ θc, at which all modes collapse into one single line or convert to modes following a quadratic law, and the intensities increase rapidly when θ approaches θc. We explain such behavior using spin wave modes in thin film with parabolic dependence of magnetization. A good agreement of this theory with the experiments on the reduced Ca-rich CaGe : YIG film has been obtained.

Magneto-optics of multilayers with arbitrary magnetization directions.

Equations are derived for determining magneto-optic coefficients in multilayer systems with arbitrary directions of their magnetizations. The equations are cast in a matrix form that is suitable for numerical simulations. This establishes a framework for calculating the Kerr and Faraday effects for a multilayer system in much the same way as has been applied previously to the bulk. Numerical Kerr results are presented for the following systems: bulk Fe, an overlayer of 50 \AA{} of Fe on Au, and for an Fe/Au superlattice for different directions of the magnetization and different angles of incidence.

Magnetostatic wave propagation in YIG double layers

Calculations are presented for the magnetostatic surface wave propagation characteristics in single-crystal yttrium-iron-garnet (YIG) double layers with arbitrary direction of magnetization. The induced uniaxial magnetic anisotropy field is assumed to be different in the two layers; hence, the magnetization in one layer is aligned at an angle with respect to the magnetization direction in the other layer. The magnetostatic field interactions between layers depend on the angle between the two magnetization directions and on the separation between the two YIG layers. The wave propagation directions and time delays in each layer can be strongly affected by the use of an applied magnetic field and the magnetostatic coupling between the two layers, as well as by the uniaxial anisotropy energy in each layer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Continuous steering of MSSW waves in YIG double layers

In this paper we report on the calculations for the magnetostatic wave propagation characteristics in single-crystal double layers of yttrium iron garnet with arbitrary direction of magnetization. The induced uniaxial magnetic anisotropy field is assumed to be different in the two layers, and hence the magnetization in one layer is aligned at an angle with respect to the magnetization direction in the other layer. The magnetostatic surface wave propagations with the greatest bandwidths and the maximum energy deliveries in each layer can be strongly affected by the application of an applied magnetic field and the magnetostatic coupling between the two layers.

Magnetization energy of polycrystalline cubic materials

The magnetization energy of a polycrystalline cubie material is determined for an arbitrary magnetization direction in polycrystals whose grains are distributed according to a Gaussian-like law, characterized by a single parameter τ, and having a uniaxial or a cubic symmetry. The theory can be applied to obtain from the magnetization energy of a polycrystal along different directions the grain dispersion parameter τ and the crystalline anisotropy constantsK1 andK2. Applications to a grain-oriented Fe-Si 3% lamination are given.