Exploring the ultrafast demagnetization of the magnetic films in ultrathin regime by element-resolved extreme ultraviolet magneto-optical spectroscopy

Ming-Shian Tsai^1,2*, Li-Han Chang¹, Bo-Yao Wang², Ming-Chang Chen^1,3,4

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
⁴Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Ming-Shian Tsai, email:s0223021@gmail.com

A new research field of "ultrafast demagnetization" has flourished in recent years because of the development of femtosecond laser technology and the demand for thermally-assisted magnetic recording [1]. Although the research of ultrafast demagnetization has been conducted in many bulk-like magnetic materials, the exploration of low-dimensional magnetic thin film systems that require in-situ preparation and measurement environments is still lacking. In this work, we study the ultrafast demagnetization effects on Ni and Co magnetic ultrathin films via a newly-developed multi-functional ultrahigh vacuum system; this system combines functions of in-situ sample preparation/characterization and a time-resolved resonant magneto-optical Kerr effect (TR-MOKE) spectroscopy with an extreme ultraviolet (EUV) tabletop light source produced by high harmonics generation (HHG). The fluence dependent measurement at the M_2,3 edge shows that the demagnetization curves as well as fast/slow recovery of magnetization can be well explained by the three-temperature model without correction of depth-dependent effect. This clarifies the uncertainty of the model applied previously in the bulk-like magnetic materials [2]. In addition, the crucial roles of Curie temperature on the ultrafast demagnetization are demonstrated through the experiments with systematic control of pumping fluence and the film thickness in ultrathin regime. Furthermore, the coupling effects between the Co and Ni layer across a Cu spacer layer under ultrafast demagnetization can further be unveiled by the element-resolved TR-MOKE at the M_2,3 edge.

[1] T. W. McDaniel, W. A. Challener, and K. Sendur, IEEE Transactions on Magnetics 39, 1972 (2003).
[2] W. You, P. Tengdin, C. Chen, X. Shi, D. Zusin, Y. Zhang, C. Gentry, A. Blonsky, M. Keller, P. M. Oppeneer, H. Kapteyn, Z. Tao, and M. Murnane, Physical Review Letters 121 (2018).

Keywords: ultrafast demagnetization, femtomagnetism, magnetic ultrathin film