Spin Excitations and Spin Structures in Low-Dimensional Ferromagnets
Tzu-Hung Chuang1*
1Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
* presenting author:Tzu-Hung Chuang, email:chuang.th@nsrrc.org.tw
A unique experimental technique, called spin-polarized electron energy loss spectroscopy (SPEELS), applied to investigate high wave-vector spin waves in low-dimensional ferromagnets will be introduced. The impact of asymmetric exchange interaction, Dzyaloshinskii-Moriya interaction (DMI), on spin-wave dispersion relation and life time has been experimentally observed by SPEELS [1]. In addition, we propose a method for probing the magnetic exchange interaction at buried interfaces using spin-polarized electrons and taking advantage of the collective nature of elementary magnetic excitations. The comparison of experimental data and first-principles calculations leads to the determination of the interface exchange parameters. This method may help the development of spectroscopy of buried magnetic interfaces [2-3].
In a system with strong DMI, chiral magnetic domain wall structures or skyrmions can be stabilized. Recently, these chiral spin structures have been observed by x-ray magnetic circular dichroism (XMCD) based photoemission electron microscope (XPEEM) at room temperature [4]. A possible investigation of non-collinear spin structures by XPEEM will be discussed.
A new generation of XPEEM end-station, which will be established at Taiwan Photon Source (TPS), will be introduced, and possible scientific opportunities will also be presented.

[1] Kh. Zakeri, et al., Phys. Rev. Lett. 104, 137203 (2010);.Kh. Zakeri, et al., Phys. Rev. Lett. 108, 197205 (2012).
[2] Kh. Zakeri, T.-H. Chuang, et al., Nature Nanotech. 8, 853 (2013).
[3] T.-H. Chuang, et al., Phys. Rev. B 89, 174404 (2014).
[4] O. Boulle, et al., Nat. Nanotech. 11, 449 (2016).

Keywords: spin waves, SPEELS, Dzyaloshinskii-Moriya interaction, XPEEM, skyrmions