Intercalated europium metal in epitaxial graphene on SiC

Abstract

X-ray magnetic circular dichroism (XMCD) reveals the magnetic properties of intercalated europium metal under graphene on SiC(0001). The intercalation of Eu nanoclusters (average size 2.5 nm) between graphene and SiC substate are formed by deposition of Eu on epitaxially grown graphene that is subsequently annealed at various temperatures while keeping the integrity of the graphene layer. Using sum-rules analysis of the XMCD of Eu M4,5 edges at T=15 K, our samples show paramagnetic-like behavior with distinct anomaly at T≈90 K, which may be related to the Nèel transition, TN=91 K, of bulk metal Eu. We find no evidence of ferromagnetism due to EuO or antiferromagnetism due to Eu2O3, indicating that the graphene layer protects the intercalated metallic Eu against oxidation over months of exposure to atmospheric environment. X-ray magnetic circular dichroism (XMCD) reveals the magnetic properties of intercalated europium metal under graphene on SiC(0001). The intercalation of Eu nanoclusters (average size 2.5 nm) between graphene and SiC substate are formed by deposition of Eu on epitaxially grown graphene that is subsequently annealed at various temperatures while keeping the integrity of the graphene layer. Using sum-rules analysis of the XMCD of Eu M 4,5 edges at T = 15 K, our samples show paramagnetic-like behavior with distinct anomaly at T ≈ 90 K, which may be related to the Nèel transition, T N = 91 K, of bulk metal Eu. We find no evidence of ferromagnetism due to EuO or antiferromagnetism due to Eu 2 O 3 , indicating that the graphene layer protects the intercalated metallic Eu against oxidation over months of exposure to atmospheric environment. Disciplines Materials Science and Engineering | Metallurgy

Intercalated rare-earth metals under graphene on SiC

“…The field dependence of the XMCD does not show hysteresis or anisotropy that is characteristic of ferromagnetic systems. We note that Eu 3+ in Eu 2 O 3 has no magnetic moment based on Hund's rules (i.e., J = 0) , and thus has no XMCD signal [21], while Dy 2 O 3 and Gd 2 O 3 have a non-zero J exhibiting detectable XMCD signal. A common challenge with intercalation is the determination of the coverage that is achieved postintercalation.…”

“…We have recently reported our results on intercalated Eu under graphene [21]. Briefly, the intercalated Eu forms nano-clusters at nucleation sites located at the vertices of the 6×6 superstructure formed by the graphene on SiC (Fig.…”

“…Higher resolution STM images ( Fig. 1 d and f) show that bright spots of the intercalated metal are now situated below the graphene [21].…”

“…The XMCD signal is obtained from the difference between two XAS spectra of the left-and right-handed helicities, µ + and µ − . More details on data reduction is provided elsewhere [12,21].…”

“…[13] It has also been demonstrated that high density magnetic islands can be grown on graphene. [14,15,16,12] In addition to modifying the electronic properties of graphene, intercalated metals can be protected to a certain degree against chemical reaction with the environment [17,18,19,20,21]. RE metals have been intercalated into bulk graphite to form graphite intercalation compounds (GICs) for quite sometime, mostly forming an inplane super structure √ 3 × √ 3R30 • at a saturated stoichiometry C 6 RE (i.e., stage I RE-GIC).…”