Reconfigurable magnetic domain-wall device: Fabrication and simulations

Abstract

The design of ultra-dense, low-cost and low-power technologies is one of the current challenges belonging to future Nanoscience and Nanotechnology breakthroughs. They represent advances which can qualitatively improve Information Technologies and strongly impact in the nowadays society. Among other important topics, the research on novel magnetic systems is a key factor to successfully accomplish these challenges. In this framework the present work moves in the direction of reconfigurable magnetic devices: systems where the response of the device can be controlled through an external agent. In the present work, a hybrid device based on the racetrack idea, is micromagnetically simulated and fabricated to control the propagation of domain walls (DW) through a Magnetic Nanowire (MNW). Simulations are performed using the Mumax3 code, and the system is fabricated by multilevel electron beam lithography procedures. A 75000x500x12 nm3 Co MNW is defined in contact with a μm diameter disc. The later acts as the magnetic domain nucleation region for the MNW. Disc shaped structures with 3 μm in diameter are defined in a different lithography step around the MNW. These discs are fabricated with amorphous NdCo5, a weak Perpendicular Magnetic Anisotropy (PMA) material. To allow magnetoresistive characterization, six Cu paths are defined in the last fabrication step on top of the previously fabricated system. The key factor for the novel functionality (“Reconfigurability”) of the proposed device is the difference between the magnetic properties of the weak PMA elements and the MNW. Specifically, the larger coercive field exhibited by the NdCo5 discs allows the DW propagation by the application of biasing fields and/or polarized currents through the MNW, without changing their magnetization configuration. In this way, the discs present a non-volatile memory which can be pre-configured by changing the magnetic history. Depending on the magnetic state recorded in the discs, different magnetostatic fields are present in the vicinity of the MNW locally leading to controllable pinning effects acting on the DW. The simulation results show that the proposed device is sensitive to the chirality of the Néel transverse DWs leading to filtering/rectifying capabilities.