Current-induced perpendicular effective magnetic field in magnetic heterostructures

Abstract

The generation of perpendicular effective magnetic field or perpendicular spins ( σz) is central for the development of energy-efficient, scalable, and external-magnetic-field-free spintronic memory and computing technologies. Here, we report the first identification and the profound impacts of a significant effective perpendicular magnetic field that can arise from asymmetric current spreading within magnetic microstrips and Hall bars. This effective perpendicular magnetic field can exhibit all the three characteristics that have been widely assumed in the literature to “signify” the presence of a flow of σz, i.e., external-magnetic-field-free current switching of uniform perpendicular magnetization, a sin 2 φ-dependent contribution in spin-torque ferromagnetic resonance signal of in-plane magnetization ( φ is the angle of the external magnetic field with respect to the current), and a φ-independent but field-dependent contribution in the second harmonic Hall voltage of in-plane magnetization. This finding suggests that it is critical to include current spreading effects in the analyses of various spin polarizations and spin–orbit torques in the magnetic heterostructure. Technologically, our results provide a perpendicular effective magnetic field induced by asymmetric current spreading as a novel, universally accessible mechanism for efficient, scalable, and external-magnetic-field-free magnetization switching in memory and computing technologies.

Room temperature field-free switching of perpendicular magnetization through spin-orbit torque originating from low-symmetry type II Weyl semimetal

“…It is known that the unconventional field-like SOT can also be caused by the Oersted field ( 51 ), which usually shows a frequency dependence ( 50 ). Therefore, we plot | S 0 / A 1 | (corresponding to the unconventional field-like SOT) and | A 0 / A 1 | (corresponding to the unconventional damping-like SOT) as a function of microwave frequencies in fig.…”

Frontiers in all electrical control of magnetization by spin orbit torque

“…Furthermore, the bending or the non-uniform current effect has been employed to achieve electrical switching in SOT-MTJ devices without external magnetic field [101][102][103][104]. As illustrated in figure 10(e), a bending structure is introduced in the SOT channel, generating a bent charge current and subsequently producing a spatially non-uniform spin current (figure 10(f)) [101].…”

Switching of Perpendicular Magnetization by Spin–Orbit Torque

“…[66,67] Note that an in-plane charge current in a perpendicularly magnetized ferromagnet, which has different conductivities for the majority and minority carriers, can generate perpendicular spins flowing in the current direction (as in the case of STT devices) but not in the perpendicular direction required for SOT applications. Care is also needed to conclude the generation of perpendicular spins since non-uniform current effects [68] can also exhibit the characteristics that have been widely assumed to "signify" the presence of a flow of perpendicular spins, i.e., a sin2φ-dependent contribution in spin-torque ferromagnetic resonance (ST-FMR) signal of in-plane magnetization (φ is the angle of the external magnetic field with respect to the current), a φ-independent but field-dependent contribution in the second harmonic Hall voltage of in-plane magnetization, and external-field-free current switching of perpendicular magnetization.…”

“…Very recently, external-magnetic-field-free SOT switching of uniform perpendicular magnetization has also been achieved by the damping-like spin-orbit torque of transverse spins and an effective perpendicular magnetic field arising from current spreading near electrical contacts or asymmetric spin Hall channel of magnetic heterostructures [68] (Figure 8a). Utilizing such an effective perpendicular magnetic field, Liu and Zhu have demonstrated the electrical switching of polycrystalline Pt/FeTb bilayers with a giant perpendicular magnetic anisotropic field of 30 kOe and a large coercivity of 0.5 kOe in absence of an external magnetic field (Figure 8b).…”