Fig. 2: Magnetoreflectance spectra and spin splittings of monolayer, bilayer and trilayer WS2 on FePS3 and SiO2 at 7 K.
From: Ferromagnetism emerged from non-ferromagnetic atomic crystals
a–d Magnetoreflectance spectra of monolayer WS2 on SiO2 a, and monolayer b, bilayer c, and trilayer d WS2 on thick FePS3. Red and blue dots represent reflectance spectra of left and right circular polarized lights. Solid lines were fitted using a complex (absorptive plus dispersive) Fano line shape to extract the absorption transition energies. Magnetoreflectance spectra of bilayer and trilayer WS2 on SiO2 are presented in Figs. S3a, b. e–g Spin splittings of monolayer e, bilayer f, and trilayer g WS2 on FePS3 and on SiO2, respectively. All different layers of WS2 on SiO2 exhibit the intrinsic Zeeman effect ~ −0.2 meV/T. Monolayer WS2 on FePS3 exhibit the intrinsic Zeeman effect as well. In stark contrast, bilayer and trilayer WS2 on FePS3 show an order of magnitude enhancements in lower magnetic field range −3.5 ~ 3.5 T, and saturate beyond 3.5 T. After saturation, the splitting drops slightly following the intrinsic Zeeman effect caused by external magnetic field. The “S”-shape magnetic field dependent spin splitting reveals the presence of interfacial ferromagnetism. The steeper slope in the low magnetic field range and the larger saturated spin splitting for the trilayer WS2/FePS3 heterostructure, compared with the bilayer WS2/FePS3 heterostructure, shows the stronger ferromagnetism. In g, the overall shift of the hysteresis loop to −0.5 ~ −1 T indicates a possible formation of an exchange bias between the ferromagnetic surface and the bulk of the antiferromagnetic FePS3 substrate. Error bars arise from the uncertainty of fitted dip positions. The dip extraction of the magnetoreflectance spectra is explained in Fig. S2 and related texts in supplementary information, and the magnetoreflectance spectra of the bilayer and trilayer WS2 on SiO2 are shown in Fig. S3.
