Absence of Magnetic Proximity Effect at the Interface of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and $(\mathrm{Bi},\mathrm{Sb}{)}_2{\mathrm{Te}}_3$ with EuS

We performed x-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the $(\mathrm{Bi},\mathrm{Sb}{)}_2(\mathrm{Se},\mathrm{Te}{)}_3$ family and the magnetic insulator EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of $\sim {10}^{-3}{\mu }_B/\mathrm{at}$.

Figure 1

(a) Averaged XAS spectra at the Eu $M_{4,5}$ edges for ${\mathrm{Bi}}_2{\mathrm{Se}}_3/\mathrm{EuS}$, ${\mathrm{Bi}}_2{\mathrm{Te}}_3/\mathrm{EuS}$, $(\mathrm{Bi},\mathrm{Sb}{)}_2{\mathrm{Te}}_3/\mathrm{EuS}$, ${\mathrm{Sb}}_2{\mathrm{Te}}_3/\mathrm{EuS}$, ${\mathrm{Sb}}_2{\mathrm{Te}}_3/\mathrm{EuS}/\mathrm{Se}$ samples and comparison with the spectrum calculated for ${\mathrm{Eu}}^{2+}$ $4f^7$, as well as (b) EuS and (c) ${\mathrm{Eu}}_2{\mathrm{O}}_3$ references. Reference spectra have been vertically shifted for clarity. (d) XMCD spectra for all samples and references. Dashed vertical lines mark the main features for ${\mathrm{Eu}}^{2+}$ (peaks $B$ and $D$) and ${\mathrm{Eu}}^{3+}$ (peaks $A$, $C$, and $E$) around the $M_5$ edge. Measurements were performed at 3 K under 2 T magnetic field applied in grazing incidence.

Figure 2

Hysteresis loops recorded at the Eu $M_5$ edge for (a) ${\mathrm{Bi}}_2{\mathrm{Te}}_3/\mathrm{EuS}$, (b) ${\mathrm{Sb}}_2{\mathrm{Te}}_3/\mathrm{EuS}/\mathrm{Se}$, and (c) ${\mathrm{Bi}}_2{\mathrm{Se}}_3/\mathrm{EuS}$ samples, measured in grazing incidence at 3 K (black triangles) and 20 K (red circles).

Figure 3

Experimental spectra for left- and right-circularly polarized x rays. XAS (top panel) and XMCD (bottom panel) at the (a) Bi $M_{4,5}$ and (b) Se $L_3$ edges for ${\mathrm{Bi}}_2{\mathrm{Se}}_3/\mathrm{EuS}$ and the (c) Sb $M_{4,5}$ and (d) Te $M_5$ edges for ${\mathrm{Sb}}_2{\mathrm{Te}}_3/\mathrm{EuS}$. The XMCD signal at the Se $L_3$ edge for the ${\mathrm{Sb}}_2{\mathrm{Te}}_3/{\mathrm{Bi}}_2{\mathrm{Se}}_3/\mathrm{EuS}$ sample has been included in (b) for comparison (vertically shifted for clarity). Measurements were performed at 3 K under a magnetic field of 2 T applied along the normal. Dashed lines mark the energy at which the XMCD features are expected to appear.