Non-Collinear Domain Wall Spin-Structure at Ultrathin Magnetic Interfaces and Its Evolution by Oxygen Adsorption
Tzu-Hung Chuang1*, Chih-Heng Huang2, Kun-Ta Lu1, Chun-I Lu1, Yen Huang3, Der-Hsin Wei1,2,3
1Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Program for Synchrotron Radiation and Neutron Beam Applications, National Sun Yat-sen University, Kaohsiung, Taiwan
3Graduate Program for Science and Technology of Synchrotron Light Source, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Tzu-Hung Chuang,
The study of non-collinear spin structures has recently attracted much attention, since manipulating these magnetic textures offers a possibility to achieve fast ultrahigh-density data manipulation. The origin of the chirality is caused by the anti-symmetric exchange interaction, i.e. Dzyaloshinskii-Moriya interaction (DMI). Large DMI has been predicted and observed at interfaces between heavy metals and transition metal ferromagnets, resulting in asymmetric spin wave dispersion relation [1-2] and chiral spin structures, such as Skyrmions within external magnetic field at low temperature [3]. Recently, these chiral spin textures have been observed by X-ray magnetic circular dichroism (XMCD) based photoemission electron microscope (XPEEM) at room temperature without external field in the system of MgO covered Co/Pt [4], demonstrating the possibilities of investigating chiral spin structures by XPEEM. In the other hand, a real-space imaging of magnetic stripe domain structures in epitaxial Fe/Ni bilayers grown on Cu(001) [5] and Co/Ni multilayers grown on Pt(111) or Ir(111) [6] has suggested the existence of Néel-type chiral domain walls with a fixed chirality at room temperature by spin-polarized low energy electron microscopy (SPLEEM), which indicates that the underlying mechanism is the DMI [5].
Here we report that by using XPEEM with XMCD contrast at BL05B2 end-station at Taiwan Light Source a Néel-type out-of-plane chiral magnetic domain wall structure was observed in epitaxial Fe/Ni/Cu(001) within the spin reorientation transition (SRT). The information of a fixed right-handed chirality can be obtained from a high-resolution XPEEM image with a line-profile of the intensity of the XMCD contrast, which is in line with the result of SPLEEM [5]. Furthermore, by taking the advantage of the synchrotron-based element-selective technique, it is found that the spin structure in Fe films is ferromagnetically coupled to the one in Ni films in this system. In addition, the evolution of the stripe domains by the oxygen adsorption is also presented and discussed.
The project is financially supported by Ministry of Science and Technology (MOST 105-2112-M-213 -012 -MY2).

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Keywords: XMCD-PEEM, Dzyaloshinskii-Moriya interaction, domain wall, spin spiral, magnetic interface