Asymmetric depinning of chiral domain walls in ferromagnetic trilayers

Abstract

We show that the coupling between two ferromagnetic layers separated by a nonmagnetic spacer can be used to control the depinning of domain walls and induce unidirectional domain wall propagation. We investigated CoFeB/Ti/CoFeB trilayers where the easy axis of the magnetization of the top CoFeB layer is out-of-plane and that of the bottom layer is in-plane. Using Magneto-optic Kerr effect microscopy, we find that the depinning of a domain wall in the perpendicularly magnetized CoFeB layer is influenced by the orientation of the magnetization of the in-plane layer, which gives rise to a field-driven asymmetric domain expansion. This effect occurs due to the magnetic coupling between the internal magnetization of the domain wall and the magnetization of the in-plane CoFeB layer, which breaks the symmetry of updown and down-up homochiral Néel domain walls in the perpendicular CoFeB layer. Micromagnetic simulations support these findings by showing that the interlayer coupling either opposes or favors the Dzyaloshinskii-Moriya interaction in the domain wall, thereby generating an imbalance in the depinning fields. This effect also allows for artificially controlling the chirality and dynamics of domain walls in magnetic layers lacking a strong Dzyaloshinskii-Moriya interaction. I-INTRODUCTION The development of future magnetic memory and logic technologies requires efficient control of magnetization in nanometer-sized devices 1. In a ferromagnet (FM), information can be encoded in magnetic domains and manipulated by displacing them 2,3. A variety of device concepts based on domain wall (DW) motion has been proposed for memory and logic operations 4-6. Many of these proposals rely on unidirectional DW motion along a racetrack, which can be easily achieved by current-induced spin-torques 7-16 , rather than externally applied magnetic fields 3 .

Asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction

“…2 for the current switching data). Here, the D s values are adapted from previous reports on corresponding magnetic interfaces that have similar sharpness and interfacial PMA energy density as our samples do in this study (i.e., D s is 0.21 × 10 −7 erg/cm for Ir/FeCoB 49 , 0.38 × 10 −7 erg/cm for W/FeCoB 51 , 0.22 × 10 −7 erg/cm for Ta/FeCoB 52 , 0.06 × 10 −7 erg/cm for Ti/FeCoB 53 , 1.2 × 10 −7 erg/cm for Pt/Co 38 , 0.34 × 10 −7 erg/cm for Ir/Co 49 and 0.01 × 10 −7 erg/cm for Pd/Co 54 , also see Supplementary Table 1 ). Note that quantification of the D s values of these PMA samples from standard Brillouin light scattering (BLS) or loop shift measurements is prevented because the electromagnet of BLS setups available to us (≤ 2 kOe) 38 , 55 cannot overcome the strong PMA field of our samples (up to 10 kOe, see Supplementary Table 1 ) to align the magnetization in-plane for the BLS analysis and because the strong dependence of the switching field on the in-plane field at zero dc current (Fig.…”

Chiral Interlayer Exchange Coupling for Asymmetric Domain Wall Propagation in Field-Free Magnetization Switching

“…Therefore, a stray field is unlikely to be the dominant contribution to B eff , since the stray field applied on the 0.9 nm CoFeB by the 3 nm CoFeB should be antiparallel to the exchange bias . In addition, orange-peel coupling , is unlikely to account for B eff . It depends on interfacial roughness instead of IP exchange bias.…”

Control of field- and current-driven magnetic domain wall motion by exchange bias in Cr2O3/Co/Pt trilayers

“…Out-of-plane (OOP) magnetized ferromagnet/heavy metal (FM/HM) layers are very promising in this respect because their strong perpendicular magnetic anisotropy results in narrow DW with simple Néel or Bloch structure, which can be easily displaced by an OOP external magnetic field [3,[14][15][16][17] or current-driven spin-orbit torques [18][19][20][21][22][23][24][25][26]. The type of DW and their chirality is determined by the Dzyaloshinskii-Moriya interaction (DMI) [19,27], and the response of DW to external stimuli in these systems can be further tuned by interfacial engineering [28][29][30][31][32], coupling to additional magnetic layers [33,34], and electric fields [35,36].…”