Field-Free Magnetization Switching in A1 CoPt Single-Layer Nanostructures for Neuromorphic Computing

Current-induced field-free magnetization switching insingle-layer films has been widely investigated for the applicationof spin-orbit torque (SOT) drivers in low-power, high-density,and nano-sized memory. In this paper, we report field-free SOT switchingwith threefold angle dependence in A1 disordered single-layer CoPtusing the MgO (111) substrate. It is found that the magnetizationcould not switch in the absence of an external in-plane magnetic fieldwhen the current was flowing in the direction of the mirror symmetryhigh-symmetry axis ([11-2]). While along the direction of thelow-symmetry axis ([1-10]) which destroyed the mirror symmetryto the greatest extent, field-free switching could be performed, andthe switching ratio was up to 30%. This was mainly attributed to thecomposition gradient-induced in-plane inversion asymmetry and thelow symmetry at the interface of Co/Pt broken out-of-plane inversion.Furthermore, CoPt devices with nanoscale thickness exhibited stablemultistate magnetic switching behavior without an external magneticfield, and simultaneously nonlinear synaptic characteristics wereobtained. A neural network was established, in which the synapticweights between the hidden layer and the output layer are updatedby using the resistance state of SOT synaptic devices, and the networkcould achieve about 90.54% recognition accuracy when applied to MNIST'shandwritten digital dataset. This work confirmed that a field-freeSOT switch could be realized in single-layer CoPt, which providedtheoretical guidance and data support for spin devices.