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Effect of spin-orbit-induced (SOI) field on magnetization reversal in ferromagnetic semiconductor GaMnAs films with 4-fold in-plane magnetic anisotropy has been investigated by planar Hall resistance (PHR) and anisotropic magnetoresistance (AMR) with current along the <110> and <100> crystallographic directions, respectively. Field scan hysteresis of PHR and AMR measured with current of 2.5 mA were observed to be asymmetric respect to zero field, showing different transition fields between positive and negative field regions. In addition, the hysteresis asymmetry is reversed as the sign of the current is reversed from positive to negative. Such dependence of asymmetry on current polarity implies that the current-induced spin-orbit field, which is known to depend on the current direction, significantly affects magnetization reversal. The asymmetry observed for currents along [100], [010], [110], and [ 1 1 ̄ 0 ] crystallographic directions is fully consistent with the effects arising from the Dresselhaus-type SOI fields in GaMnAs films. [ABSTRACT FROM AUTHOR]

We have studied spin-orbit torque (SOT) magnetization switching in a (Ga,Mn)(As,P) film with vertically-graded magnetic anisotropy. The magnetization switching chirality during current scans reveals that strain-induced Dresselhaus-type spin-orbit field does the major role for spin polarization of carriers causing SOT in the system. The volume fraction of SOT magnetization switching significantly depends on the magnitude and direction of the applied bias field. This feature leads to the realization of stable multilevel magnetic states in composition-graded (Ga,Mn)(As,P) film. The experiment demonstrates that multiple magnetic state can be robustly set by using appropriate bias fields. This characteristic can be used to realize SOT-driven multi-state memories and/or memristor devices, which are key ingredients for neuromorphic computing. [ABSTRACT FROM AUTHOR]

Spin–orbit-induced (SOI) effective magnetic field in GaMnAs film with in-plane magnetic anisotropy has been investigated by planar Hall effect measurements. The presence of SOI field was identified by a shift between planar Hall resistance (PHR) hystereses observed with positive and negative currents. The difference of switching fields occurring between the two current polarities, which is determined by the strength of the SOI field, is shown to depend on the external field direction. In this paper we have developed a method for obtaining the magnitude of the SOI fields based on magnetic free energy that includes the effects of magnetic anisotropy and the SOI field. Using this approach, the SOI field for a given current density was accurately obtained by fitting to the observed dependence of the switching fields on the applied field directions. Values of the SOI field obtained with field scan PHR measurements give results that are consistent with those obtained by analyzing the angular dependence of PHR, indicating the reliability of the field scan PHR method for quantifying the SOI-field in GaMnAs films. The magnitude of the SOI field systematically increases with increasing current density, demonstrating the usefulness of SOI fields for manipulation of magnetization by current in GaMnAs films. [ABSTRACT FROM AUTHOR]

We have investigated the exchange bias (EB) effect occurring in (Ga, Mn)As/(Ga, Mn)(As, P) bilayers, in which the (Ga, Mn)As layer has an in-plane (IP) magnetic anisotropy, and the magnetic anisotropy of the (Ga, Mn)(As, P) layer is out-of-plane (OP). Planar Hall resistance (PHR) measured during magnetization reversal in this system showed a clear shift of the hysteresis loops, indicating the presence of EB in the (Ga, Mn)As layer. The EB significantly depends on the direction of the field used in the field-cooling process. The observed EB occurring in a bilayer in which the constituent layers have orthogonal magnetic anisotropies can be understood in terms of the formation of magnetic closure domains in the (Ga, Mn)(As, P) layer during field cooling. We show that such EB can be effectively controlled by the process of field cooling, suggesting the possibility of memory device applications based on bilayer systems with orthogonal magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Spin–orbit-induced (SOI) field of crystalline GaMnAs ferromagnetic film has been investigated by using planar Hall effect measurements. The presence of SOI field manifested itself as an asymmetry in the magnetization reversal process between positive and negative current directions. A significant Joule heating caused by current has been observed and its effect was carefully considered to obtain the magnetic anisotropy of the GaMnAs film. The switching of magnetization by SOI field in the GaMnAs film was demonstrated in the absence of an external field. [ABSTRACT FROM AUTHOR]

Interlayer exchange coupling (IEC) between ferromagnetic (FM) metal Fe and FM semiconductor GaMnAs has been investigated by using magnetotransport measurements. The realization of diverse magnetization alignments, including collinear and non-collinear configurations, between Fe and GaMnAs layers are observed during the magnetization reversal process measured by the planar Hall effect. Minor loop scan reveals the presence of FM IEC between Fe and GaMnAs, which systematically decreases as the temperature increases. [ABSTRACT FROM AUTHOR]

A series of Ga1-xMnxAs1-yPy films grown by MBE on GaAs (100) substrates was systematically studied by ferromagnetic resonance (FMR). Magnetic anisotropy parameters were obtained by analyzing the angular dependence of the FMR data. The results clearly show that the easy axis of the films shifts from the in-plane [100] direction to the out-of-plane [001], indicating the emergence of a strong tensile-strain-induced perpendicular anisotropy when the P content exceeds y ≈ 0.07. Multiple resonances were observed in Ga1-xMnxAs1-yPy films with thicknesses over 48 nm, demonstrating the existence of exchange-dominated non-propagating spin-wave modes governed by surface anisotropy. [ABSTRACT FROM AUTHOR]

We carried out a systematic study of magnetic ordering and magnetic interlayer coupling in Ga1-xMnxAs1-yPy/Ga1-xMnxAs bilayers using superconducting quantum interference device magnetometry and ferromagnetic resonance. Such bilayers are interesting, because the easy axis of the constituent materials are orthogonal. Our results show that the bilayers are strongly exchange-coupled at the interface, that manifests itself in the form of horizontal exchange-bias-like shifts of the hysteresis loops of the Ga1-xMnxAs layer, as observed in field-cooled magnetic measurements. [ABSTRACT FROM AUTHOR]

We have investigated magnetic properties of Ni film specimens deposited either on GaAs or on Bi2Se3 surfaces. The magnetization saturation field along the out-of-plane direction observed in the Hall data was weaker for the Ni/Bi2Se3 sample than for the Ni/GaAs sample. On the other hand, planar Hall resistance measurements showed the larger in-plane coercive field for Ni/Bi2Se3 than for Ni/GaAs. These changes of magnetic hardness observed along the out-of-plane and in-plane directions in the Ni/Bi2Se3 specimen are consistent with effects arising from spin–orbit interaction at the surface of the Bi2Se3 topological insulator. [ABSTRACT FROM AUTHOR]

We discuss magnetic properties of lithographically patterned nanoscale stripes of dilute ferromagnetic semiconductor (Ga,Mn)As aligned with [110] crystallographic direction, i.e., perpendicular to the easy axis of uniaxial magnetocrystalline anisotropy of this material. We find that at temperatures where uniaxial anisotropy becomes dominant, shape-induced effects strongly compete with this intrinsic property, tending to align the total magnetization along the stripe direction. The present study revealed, however, that low-temperature annealing of the stripes markedly reduces such shape-induced effects. This effect of annealing is not presently understood, and will require further detailed study. [ABSTRACT FROM AUTHOR]

We report a systematic investigation of ac magnetic susceptibility in (Ga,Mn)As films as a function of temperature and magnetic field, carried out in parallel with dc magnetization measurements. The temperature dependence of ac susceptibility \chi ac shows anisotropic behavior: 1) a single peak in \chi ac is observed close to TC for the [ 1\bar 10 ] orientation of the driving ac field; 2) a single peak is also seen close to 22 K for the field along [110]; and 3) peaks at both these temperatures are observed for the field applied along [100]. A detailed analysis of the ac and dc data unambiguously indicates that the peak near TC is related to the paramagnetic-to-ferromagnetic phase transition, with the ferromagnetic domains nucleating with their easy axes aligned with the [ 1\bar 10 ] direction, providing a clear picture of uniaxial domain behavior near TC . The peak near 22 K, on the other hand, is related to the onset of biaxial domain structure in (Ga,Mn)As induced by the competition between uniaxial and cubic anisotropy. More specifically, the ac susceptibility peak near TC involves 180° magnetization flips along the [ 1\bar 10 ] easy axis of the domains, while the peak near 22 K originates from magnetization wobbling between two biaxial easy axes separated by a small angle. [ABSTRACT FROM AUTHOR]

Interlayer exchange coupling (IEC) between the GaMnAs layers in GaMnAs/GaAs:Be multilayer systems has been investigated using magnetotransport experiments. The observation of a stable antiparallel magnetization alignment state from the systems indicates the presence of antiferromagnetic (AFM) IEC between the GaMnAs layers. The transitions between parallel and antiparallel alignments of GaMnAs magnetic layers in the system were carefully investigated by measuring resistance change with increasing temperature under various bias magnetic fields. From the dependence of the transition temperature on bias fields, we have estimated the magnitude of AFM IEC and its temperature behavior of our GaMnAs/GaAs:Be multilayers. [ABSTRACT FROM AUTHOR]

We report the realization of ten stable tunneling magnetoresistance (TMR) states in a single device. To achieve ten resistance states, we have used a magnetic tunnel junction (MTJ) structure that consists of two magnetic layers, which are Fe and GaMnAs ferromagnetic layers. Owing to the two in-plane magnetic easy axes that result from strong cubic anisotropies in both Fe and GaMnAs layers, noncollinear magnetic configurations between two magnetic layers were realized, in addition to the parallel and antiparallel configurations. Such noncollinear magnetic configurations provide stable intermediate TMR values between two extreme values corresponding parallel and antiparallel configurations. The number of stable TMR values was further increased by forming multidomain structures in the MTJ structure. We demonstrate that we can obtain up to ten stable TMR values, and they can be controlled by applying the appropriate magnetic field sequences. [ABSTRACT FROM AUTHOR]

The newly-developing spintronics technology requires materials that allow control of both the charge and the spin degrees of freedom of the charge carriers. Ferromagnetic semiconductors (SC) are considered suitable due to simultaneous presence of magnetic order and of semiconducting properties. GaMnAs is one of the most intensively studied ferromagnetic SC. In this paper we will review recent research and accomplishments regarding two technologically important properties – magnetic anisotropy and interlayer coupling — of GaMnAs-based multilayer structures, with an eye on their potential role in practical devices. [Copyright &y& Elsevier]

In order to investigate the origin of the magnetic circular dichroism (MCD) in Ga1-xMnx, As, we prepared a series of paramagnetic samples with a very low Mn content (x ~ 0.0005 and 0.0003), grown at different substrate temperatures. The samples grown at low temperatures (< 300 °C) show a sign change in the MCD, while those grown at higher temperatures (> 300°C) reveal broad positive MCD spectra similar to those observed in ferromagnetic Ga1-xMnxAs. In addition, samples grown at high temperature (~600 °C) but with Si co-doping show a behavior typical to samples grown at low substrate temperatures, namely sign changing MCD spectra. Our results indicate that the negative component of the MCD does not originate from the interband transitions but from transitions involving ionized Mn acceptors. [ABSTRACT FROM AUTHOR]

In this paper, we report a systematic study on the temperature dependences of the exchange bias (EB) field HEB and coercivity HC in (Ga,Mn)As-MnO bilayers via magnetotransport measurements. Structures of (Ga,Mn)As-Mn were grown by molecular beam epitaxy, and then oxidized to obtain a top layer of MnO. Different methods were used to oxidize the Mn, and their effects on the behavior of HEB and HC were studied. It is a striking result that, once the structure is field-cooled from room temperature to 4.2 K, HEB retains its value even after warming the structure to 130 K, indicating that the exchange coupling sustains the ordering in MnO above the Néel temperature TN (110 K) of bare MnO. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed investigation of exchange-dominated nonpropagating spin-wave modes in a series of 100-nm Ga1-xMnxAs films with Mn concentrations x ranging from 0.02 to 0.08. The angular and Mn concentration dependences of spin-wave resonance (SWR) modes have been studied for both as-grown and annealed samples. Our results indicate that the magnetic anisotropy terms of Ga1-xMnxAs depend on the Mn concentration x, but are also strongly affected by sample growth conditions; moreover, the magnetic anisotropy of Ga1-xMnxAs films is found to be clearly linked to the Curie temperature. The SWR spectra consist of a series of well-resolved standing spin-wave modes. The observed mode patterns are consistent with the Portis volume-inhomogeneity model, in which a spatially nonuniform anisotropy field acts on the Mn spins. The analysis of these exchange-dominated spin-wave modes, including their angular dependences, allows us to establish the exchange stiffness constants for Ga1-xMnxAs films. [ABSTRACT FROM AUTHOR]