Interlayer exchange coupling (IEC) has been intensively investigated in magnetic multilayers, owing to its potential for magnetic memory and logic device applications. Although IEC can be reliably obtained in metallic ferromagnetic multilayer systems by adjusting structural parameters, it is difficult to achieve gate control of IEC in metallic systems due to their large carrier densities. Here, we demonstrate that IEC can be reliably controlled in ferromagnetic semiconductor (FMS) trilayer structures by means of an external gate voltage. We show that, by designing a quantum-well-type trilayer structure based on (Ga,Mn)(As,P) FMSs and adapting the ionic liquid gating technique, the carrier density in the nonmagnetic spacer of the system can be modulated with gate voltages of only a few volts. Due to this capability, we are able to vary the strength of IEC by as much as 49% in the FMS trilayer. These results provide important insights into design of spintronic devices and their energy-efficient operation.

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.

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 [Formula: see text] crystallographic directions is fully consistent with the effects arising from the Dresselhaus-type SOI fields in GaMnAs films.

We report an investigation of current-induced spin–orbit fields (SOFs) in a crystalline (Ga,Mn)As ferromagnetic film with four-fold in-plane anisotropy. By designing a Hall device with current channels along crystallographic 〈100〉 directions, we observe the effects of SOFs in all four magnetization transitions over the four 〈110〉 hard axes of the film. The SOF effects are observed in the form of opposite shifts of angles at which the magnetization of the film switches sign for opposite current polarities in anisotropic magnetoresistance (AMR) measurements carried out as the applied magnetic field was rotated. Note that the Dresselhaus- and Rashba-type SOFs generated by currents flowing along the 〈100〉 directions—as in the device designed for the present experiments—are orthogonal to one another and can thus be separated by appropriate analysis of AMR. The analysis of experimental results based on magnetic free energy, in which the effects of SOFs are included, reveals that the Dresselhaus-type SOF is much stronger than the Rashba-type SOF. The values of the two SOFs obtained independently with currents flowing either along the [100] or [010] channels are consistent with each other, showing the reliability of the above-mentioned approach for investigating SOFs in ferromagnetic films.

Switching of magnetization by spin–orbit torque in the (Ga,Mn)(As,P) film was studied with currents along ⟨100⟩ crystal directions and an in-plane magnetic field bias. This geometry allowed us to identify the presence of two independent spin–orbit-induced magnetic fields: the Rashba field and the Dresselhaus field. Specifically, we observe that when the in-plane bias field is along the current (I[Formula: see text]H bias), switching is dominated by the Rashba field, while the Dresselhaus field dominates magnetization reversal when the bias field is perpendicular to the current (I ⊥ H bias). In our experiments, the magnitudes of the Rashba and Dresselhaus fields were determined to be 2.0 and 7.5 Oe, respectively, at a current density of 8.0 × 105 A/cm2.