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Theme 3 colloquium by dr. Heiko Wende: ' Element specific insight into the magnetism of 3d and 4f based hybrid systems on graphene' (Lecture)

Date
Tuesday 18 February 2020Add to my calendar
Time
from 16:00
Location
HGH00.307
Speaker
dr. Heiko Wende (University of Duisburg-Essen and CENIDE, Germany)
Description

Heiko WendeThe usage of graphene in surface spin-hybrid systems offers the possibility to tailor magnetic properties of the individual magnetic building blocks. By intercalation of graphene with rare earth systems for example a (√3×√3)R30° superstructure of Eu with respect to the graphene lattice can be stabilized on Ni or Co films on Ir(111) [1]. Interestingly, the intercalated Eu lifts the hybridization of the Ni or Co 3d orbitals with the π orbitals of graphene and thereby decouples graphene electronically. The antiferromagnetic coupling of Ni or Co films to Eu is found to be so strong that even at room temperature a finite magnetization of the Eu system can be revealed by XMCD [1]. Another possibility to utilize graphene in hybrid systems is the modification of the magnetic properties of magnetic molecules [2]. We have shown by XMCD investigations that the magnetic coupling of Fe-phthalocyanine or Co-porphyrin molecules to ferromagnetic films can designed by graphene [3,4]. This also holds for single molecular magnets as e.g. Ln(III) bis-phthalocyanines that show an antiferromagnetic coupling to a Ni(111) substrate [5]. The spin radical on the Pc ring actually survives when graphene is utilized in between the TbPc2 molecules and the Ni(111) surface [6]. Finally, I will show results of an element specific study of Eu-cyclooctatetraene (EuCot) nanowires on graphene/Ir(111). We analyze the magnetic coupling of the Eu ions in these organometallic sandwich molecular nanowires by XMCD. Field-dependent measurements of the XMCD signal at the Eu M5 edge show hysteresis at 5 K, thus confirming EuCot as a ferromagnetic material (see figure) [7].

[1] F. Huttmann et al., Phys. Rev. B 95, 075427 (2017)
[2] S. Bhandary et al., Phys. Rev. Lett. 107, 257202 (2011)
[3] A. Candini et al., J. Phys. Chem. C 118 (31), 17670-17676 (2014)
[4] D. Klar et al., Phys. Rev. B 89, 144411 (2014)
[5] A. Candini et al., Sci. Rep. 6, 21740 (2016)
[6] S. Marocchi et al., ACS Nano 10, 9353-9360 (2016)
[7] F. Huttmann et al., J. Phys. Chem. Lett 10, 911-917 (2019)