Accelerating laser-induced demagnetization in ferromagnetic films via optically-induced intersite spin transfer from adjacent antiferromagnetic layers

Ming-Shian Tsai^1,2*, Li-Han Chang^1,2, Ming-Chang Chen^1,3, Bo-Yao Wang²

¹Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan
²Department of Physics, National Changhua University of Education, Changhua, Taiwan
³Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Ming-Shian Tsai, email:mingshian.tsai@gapp.nthu.edu.tw

Antiferromagnetic (AFM) films are critical in advanced spintronic devices, enabling control over neighboring ferromagnetic (FM) layers via interfacial exchange coupling. However, the effects of short-pulse excitation on AFM-induced coupling within ultrafast timescales remain unclear. In this work, we systematically investigated the laser-induced ultrafast magnetic dynamics in a series of Mn/Co bilayers, which varied from paramagnetic (PM) to AFM states in the Mn films by precisely controlling the Mn film thickness. We observed a significantly faster laser-induced demagnetization rate of Co moments in AFM-Mn/Co films compared to PM-Mn/Co and Cu/Co films. Furthermore, in both PM-Mn/Co and AFM-Mn/Co films, the Mn moments display a transient enhancement coinciding with the demagnetization of Co, exhibiting a rise time comparable to the duration of the excitation pulse. Such a coherent response indicates that optically induced intersite spin transfer (OISTR) between Co and Mn is the dominant mechanism governing the early-stage ultrafast dynamics in our system. As a result, the reduction in demagnetization time of the Co layer in AFM-Mn/Co films can be attributed to the enhancement of OISTR efficiency due to the layered AFM spin structure of Mn. This finding suggests a possibility of accelerating the temporal dynamics of FM films by applying AFM layers, opening up new opportunities for ultrafast spintronics applications.

Keywords: antiferromagnetism, femtomagnetism, magnetic ultrathin films