Dynamic Binding of Driven Interfaces in Coupled Ultrathin Ferromagnetic Layers

Abstract

We demonstrate experimentally dynamic interface binding in a system consisting of two coupled ferromagnetic layers. While domain walls in each layer have different velocity-field responses, for two broad ranges of the driving field H, walls in the two layers are bound and move at a common velocity. The bound states have their own velocity-field response and arise when the isolated wall velocities in each layer are close, a condition which always occurs as H→0. Several features of the bound states are reproduced using a one-dimensional model, illustrating their general nature.

Domain wall structure in magnetic bilayers with perpendicular anisotropy

“…Such structures have been recently studied and the dynamics under field or current has been shown to be original due to the coupling between the two layers [15]. In order to gain precise information on their structure, we use a combination of MFM and ballistic electron emission microscopy (BEEM), a recent technique that allows high spatial resolution magnetization imaging.…”

Dynamic selective switching in antiferromagnetically-coupled bilayers close to the spin reorientation transition

“…3(b)) has a remarkably more abrupt evolution with dH/dt at the crossover range than the CoFeB single layer. This suggests that binding effects between layers 19 are especially important for these dH/dt values, where both layers are likely to switch. In spite of this disagreement, the simple model presented here gives account of many of the features observed in the bilayer, constituting a good starting point to select what values for film thicknesses and RKKY coupling are needed in order to design SAFs with dynamic selective switching.…”

“…Moreover, the coupling field of both layers has been extracted using an Ising approximation, whereas the reversal of the Co layer is far from being Ising-like; the exact configuration and reversal process of this layer is complex, characterization of which will be published elsewhere. Last, any possible effect of the coupling on the coercivity of the films is not taking into account in the virtual bilayer: Here the coupling is considered merely as a field shifting the coercivity of single layers; possible binding effects during the reversal of the real bilayer due to the coupling field coming from RKKY interactions 19 have not been considered. In spite of those simplifications, a quite good agreement is observed between the switching fields experimentally determined in the virtual and in the real bilayer using this analysis (comparison of Figs.…”

A robust soliton ratchet using combined antiferromagnetic and ferromagnetic interlayer couplings

“…For measurement of F coupling, we use a trilayer stack as shown in Figure 2(b), with this more complicated structure necessary to prevent the two ferromagnetically coupled layers switching together. 20 By controlling the Ru thickness, we can find the peak in the ferromagnetic coupling between the first and second antiferromagnetic peaks.…”

“…The ferromagnetic coupling breaks the symmetry of the device giving unidirectionality, which three (or more) AF couplings with magnetic layers of the same material and thickness cannot do, even if the coercivity is allowed to vary freely (see supplementary material), 17 meaning that no repeating motif soliton ratchet device is possible. Having identical magnetic layers is an advantage of this scheme, since different thickness magnetic layers have different coercivity responses in terms of frequency, [18][19][20] so although the coercivities can be similar on typical laboratory timescales of, for example, magneto-optical Kerr effect (MOKE) measurements, they may be different on fast, technologically relevant timescales. For these ratchet schemes, large variations in coercivity between layers can lead to the breakdown of ratchet behavior.…”