A Spin‐Orbit Torque Ratchet at Ferromagnet/Antiferromagnet Interface via Exchange Spring

Abstract

The antiferromagnet (AFM) and ferromagnet (FM) interface is a unique branch of magnetics of broad scientific interest. AFMs play an important role in spin-orbit torque devices based on their ability to generate spin-polarized current and exchange bias when combined with FMs. In this study, an interesting spin-orbit torque (SOT) ratchet involving the exchange spring effect in an IrMn/CoFeB bilayer device with perpendicular anisotropy and exchange bias is developed. The combined use of electrical and spectroscopic analysis reveals that the exchange spring in IrMn/CoFeB bilayer yields unidirectional anisotropy, resulting in a collinear/orthogonal AFM/FM spin configuration at the interface upon switching CoFeB magnetization upward/downward. The ratcheting characteristics resulting from unidirectional anisotropy manifest in SOT switching. In this process, magnetization against the exchange spring features digital-like switching with a sharp transition, whereas the reverse function is characteristic of analog switching with a gradual transition tail. The dual digital-analog characteristics of the IrMn/CoFeB bilayer may be of benefit in neuromorphic and memory applications.

Tunable multistate field-free switching and ratchet effect by spin-orbit torque in canted ferrimagnetic alloy

“…4c and 4d. Thus, an additional state is visible and this irreversible behavior manifests a similar SOT ratchet effect in a single layer RE-TM ferrimagnetic alloy as in AFM/FM systems 35,37,41 . SOT switching curve with varying external symmetry breaking field (B x ) and initialization with B set,z of +100 mT and -100 mT respectively.…”

“…Another signature of SOT ratchet effect is the sharpness of the switching between the two magnetic states. This is usually more prominent in system with higher saturation magnetization such as IrMn/CoFeB systems 35 , nevertheless, it is still observable here in Gd x Co 100−x . In Fig 3a and 3b, for switching curves with decent switching amplitude (|B x | > 1 mT), the amount of ∆R AHE per unit current density increase is larger when switching with positive current regardless of the chirality (down to up state for -B x and up to down state for +B x ).…”

“…This has been observed in the AFM / FM bilayer system with in-plane exchange bias field acting on the FM with PMA in past studies 23 . The fact that this behavior only shows up in one magnetic state rather than both can be due to the exchange spring effect, also the ratchet effect in SOT which is asymmetry in the magnetic state stability 35 .…”

“…In AFM/FM bi-layer systems, not only field-free switching 23,30,31 can be realized but also many interesting magnetic textures and switching behaviors such as electrical control of antiferromagnetic order 32,33 , multistate switching 23,34 , and memristor behavior 23,34 can be observed owing to its dynamic and intricate magnetic interaction at the AFM/FM interface 35 . Due to the exchange coupling at the AFM/FM interface, AFM spin configuration at the interface can be controlled via SOT and exhibits an exchange spring effect that manifests in a ratchet behavior of the magnetic states 35 and antiferromagnetic states 36,37 .…”

Large tunneling magnetoresistance in van der Waals magnetic tunnel junctions based on FeCl2films with interlayer antiferromagnetic couplings

“…8 For example, AFMs have already been widely used in different generations of magnet random access memory (MRAM), including thermally-assisted MRAM, spin transfer torque (STT) MRAM and spin orbit torque MRAM. 9–11 However, the information carriers of the above-mentioned devices are still FMs. In order to take full advantage of AFMs and further improve the performance of spintronic devices, researchers have tried various techniques to manipulate and detect the magnetic state of an AFM, for example, via film thickness engineering, strain, current-induced Joule heating and the interaction of electromagnetic radiation with AFMs.…”