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Register a new userVoltage controlled spin injection in a (Ga,Mn)As/(Al,Ga)As Zener diode
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The spin polarization of the electron current in a p-(Ga,Mn)As-n-(Al,Ga)As-Zener tunnel diode, which is embedded in a light-emitting diode, has been studied theoretically. A series of self-consistent simulations determines the charge distribution, the band bending, and the current-voltage characteristics for the entire structure. An empirical tight-binding model, together with the Landauer- Buttiker theory of coherent transport has been developed to study the current spin polarization. This dual approach allows to explain the experimentally observed high magnitude and strong bias dependence of the current spin polarization.
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A remarkable progress towards functional ferromagnetic semiconductor materials for spintronics has been achieved in p-type (Ga,Mn)As. Robust hole-mediated ferromagnetism has, however, been observed also in other III-V hosts such as antimonides, GaP or (Al,Ga)As which opens a wide area of possibilities for optimizing the host composition towards higher ferromagnetic Curie temperatures. Here we explore theoretically ferromagnetism and Mn incorporation in Ga(As,P) and (Al,Ga)As ternary hosts. While alloying (Ga,Mn)As with Al has only a small effect on the Curie temperature we predict a sizable enhancement of Curie temperatures in the smaller lattice constant Ga(As,P) hosts. Mn-doped Ga(As,P) is also favorable, as compared to (Al,Ga)As, with respect to the formation of carrier and moment compensating interstitial Mn impurities. In (Ga,Mn)(As,P) we find a marked decrease of the partial concentration of these detrimental impurities with increasing P content.
The large tunneling anisotropic magneto-resistance of a single $p^{++}$-(Ga,Mn)As/$n^{+}$-GaAs Zener-Esaki diode is evidenced in a perpendicular magnetic field over a large temperature and voltage range. Under an applied bias, the tunnel junction transparency is modified, allowing to continuously tune anisotropic transport properties between the tunneling and the ohmic regimes. Furthermore, an asymmetric bias-dependence of the anisotropic tunneling magneto-resistance is also observed: a reverse bias highlights the full (Ga,Mn)As valence band states contribution, whereas a forward bias only probes part of the density of states and reveals opposite contributions from two subbands.
We present magnetic and tunnel transport properties of (Ga,Mn)As/(In,Ga)As/(Ga,Mn)As structure before and after adequate annealing procedure. The conjugate increase of magnetization and tunnel magnetoresistance obtained after annealing is shown to be associated to the increase of both exchange energy $Delta$$_{exch}$ and hole concentration by reduction of the Mn interstitial atom in the top magnetic electrode. Through a 6x6 band k.p model, we established general phase diagrams of tunneling magnetoresistance (TMR) and tunneling anisotropic magnetoresistance (TAMR) textit{vs.} (Ga,Mn)As Fermi energy (E$_F$) and spin-splitting parameter (B$_G$). This allows to give a rough estimation of the exchange energy $Delta$$_{exch}$=6B$_G$$simeq$120 meV and hole concentration p$simeq1.10^{20}$cm$^{-3}$ of (Ga,Mn)As and beyond gives the general trend of TMR and TAMR textit{vs.} the selected hole band involved in the tunneling transport.
We report on the determination of micromagnetic parameters of epilayers of the ferromagnetic semiconductor (Ga,Mn)As, which has easy axis in the sample plane, and (Ga,Mn)(As,P) which has easy axis perpendicular to the sample plane. We use an optical analog of ferromagnetic resonance where the laser-pulse-induced precession of magnetization is measured directly in the time domain. By the analysis of a single set of pump-and-probe magneto-optical data we determined the magnetic anisotropy fields, the spin stiffness and the Gilbert damping constant in these two materials. We show that incorporation of 10% of phosphorus in (Ga,Mn)As with 6% of manganese leads not only to the expected sign change of the perpendicular to plane anisotropy field but also to an increase of the Gilbert damping and to a reduction of the spin stiffness. The observed changes in the micromagnetic parameters upon incorporating P in (Ga,Mn)As are consistent with the reduced hole density, conductivity, and Curie temperature of the (Ga,Mn)(As,P) material. We report that the magnetization precession damping is stronger for the n = 1 spin wave resonance mode than for the n = 0 uniform magnetization precession mode.
Electrical current manipulation of magnetization switching through spin-orbital coupling in ferromagnetic semiconductor (Ga,Mn)As Hall bar devices has been investigated. The efficiency of the current-controlled magnetization switching is found to be sensitive to the orientation of the current with respect to the crystalline axes. The dependence of the spin-orbit effective magnetic field on the direction and magnitude of the current is determined from the shifts in the magnetization switching angle. We find that the strain induced effective magnetic field is about three times as large as the Rashba induced magnetic field in our GaMnAs devices.
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