Local and global energy barriers for chiral domain walls in lateral magnetic junctions

The current induced manipulation of chiral spin textures is of great interest for both fundamental research and technological applications.  Of particular interest are magnetic non-volatile memories formed from synthetic antiferromagnetic (SAF) wire in which chiral composite domain walls (DWs), that act as data bits, can be efficiently moved by current [1]. However, overcoming the trade-off between energy efficiency, namely a low threshold current density and high thermal stability, remains a major challenge for the development of integrated chips with high reliability and low power consumption.  We will show that chiral DWs in a SAF-ferromagnet (FM) lateral junction, formed by local plasma oxidation, are highly stable against large magnetic fields whilst the DWs can be efficiently moved across the junction by current [2].  Our approach takes advantage of field-induced global energy barriers in the unique energy landscape of the junction that are added to the local energy barrier.  We demonstrated that thermal fluctuations are equivalent to the magnetic field effect in the energy landscape, thereby, surprisingly, increasing the energy barrier and further stabilizing the DW in the junction at higher temperatures, which is in sharp contrast with FMs or SAFs.  We found that the threshold current density can be further decreased by tilting the junction across the wire while not affecting the high DW stability.  Furthermore, we demonstrated that chiral DWs can be robustly confined within a FM region sandwiched on both their sides by SAFs and yet can be readily injected into these regions by current. Our findings break the trade-off between efficiency and stability, allowing for diverse and versatile DW-based memory, and logic, and beyond with new functionalities.

[1] See-Hun Yang, K.-S. Ryu, and S. S. P. Parkin, “Domain-wall velocities of up to 750 m s−1 driven by exchange-coupling torque in synthetic antiferromagnets”, Nature Nanotechnology 10, 221 (2015).

[2] Jiho Yoon, See-Hun Yang (corresponding author), Jae-Chun Jeon, Andrea Migliorini, Ilya Kostanovskiy, Tianping Ma, Stuart. S. P. Parkin, “Local and global energy barriers for chiral domain walls in synthetic antiferromagnet-ferromagnet lateral junctions”, Nature Nanotechnology 17, 1183 (2022).