Magnetic Patterning by Electron Beam-Assisted Carbon Lithography

Abstract

We report on the proof of principle of a scalable method for writing the magnetic state by electron-stimulated molecular dissociative adsorption on ultrathin Co on Re(0001). Intense microfocused low-energy electron beams are used to promote the formation of surface carbides and graphitic carbon through the fragmentation of carbon monoxide. Upon annealing at the CO desorption temperature, carbon persists in the irradiated areas, whereas the clean surface is recovered elsewhere, giving origin to chemical patterns with nanometer-sharp edges. The accumulation of carbon is found to induce an in-plane to out-of-plane spin reorientation transition in Co, manifested by the appearance of striped magnetic domains. Irradiation at doses in excess of 1000 L of CO followed by ultrahigh vacuum annealing at 380 °C determines the formation of a graphitic overlayer in the irradiated areas, under which Co exhibits out-of-plane magnetic anisotropy. Domains with opposite magnetization are separated here by chiral Neél walls. Our fabrication protocol adds lateral control to spin reorientation transitions, permitting to tune the magnetic anisotropy within arbitrary regions of mesoscopic size. We envisage applications in the nano-engineering of graphene-spaced stacks exhibiting the desired magnetic state and properties.

A UHV MOKE magnetometer complementing XMCD-PEEM at the Elettra Synchrotron

“…Fig. 8(a) shows the XMCD-PEEM images acquired at zero field at different temperatures between 25 and 375 C. The images show a pattern with alternating dark and bright regions, which, in agreement with our previous work, is interpreted as being due to out-of-plane domains with an antiparallel orientation of the magnetization (Genoni et al, 2018). The XMCD asymmetry is close to 6%, as expected for metallic Co in our measurement geometry (grazing incidence illumination at 16 reduces the contrast by a factor of about 3.5 for the out-of-plane magnetization compared to the in-plane magnetization).…”

“…With this motivation, we recently investigated the magnetic properties of ultra-thin Co on Re(0001), focusing our attention on the effect of carbon adsorption on the film magnetic anisotropy. Our previous work had established a means to graft the magnetic state by accumulating carbon adspecies on the cobalt surface using e-beam-stimulated CO fragmentation (Genuzio et al, 2019a;Genoni et al, 2018). Interestingly, we found that these species can be converted to a graphitic overlayer upon performing a moderate thermal treatment, without compromising the integrity of the ultra-thin Co film.…”

“…Interestingly, we found that these species can be converted to a graphitic overlayer upon performing a moderate thermal treatment, without compromising the integrity of the ultra-thin Co film. Combined photoemission spectroscopy and XMCD-PEEM measurements demonstrated that the cobalt underneath the graphene exhibits enhanced PMA (Genoni et al, 2018).…”

“…The graphene/Co(4.7 AL)/Re(0001) sample was prepared following the cleaning and Co deposition protocols described in our previous studies (Genoni et al, 2018;Genuzio et al, 2019a). The graphene layer was grown using chemical vapour deposition (CVD) of ethylene at a partial pressure in the range from 1 Â 10 À7 to 1 Â 10 À6 mbar, saturating the Co surface at room temperature and then annealing it up to about 700 K for a total time of at least 30 min (Jugovac et al, 2019).…”

Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams

“…The XMCD-PEEM images comparing the magnetic state of Co before and after air exposure are shown in parts a and b of Figure . The labels provide information on the magnetic anisotropy, which was determined in accord to our previous study on this system . Initially, the nonirradiated regions exhibit in-plane magnetization, as can be deduced from the large contrast that is observed outside the disk.…”