Study of Dy-doped Bi₂Te₃: thin film growth and magnetic properties

Abstract

Abstract. Breaking the time-reversal symmetry (TRS) in topological insulators (TIs) through ferromagnetic doping is an essential prerequisite for unlocking novel physical phenomena and exploring potential device applications. Here, we report the successful growth of high-quality (Dy x Bi 1−x ) 2 Te 3 thin films with Dy concentrations up to x = 0.355 by molecular beam epitaxy. Bulk-sensitive magnetisation studies using superconducting quantum interference device magnetometry find paramagnetic behaviour down to 2 K for the entire doping series. The effective magnetic moment, µ eff , is strongly doping concentration-dependent and reduces from ∼12.6 µ B /Dy for x = 0.023 to ∼4.3 µ B /Dy for x = 0.355. X-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Dy M 4,5 edge are employed to provide a deeper insight into the magnetic nature of the Dy 3+ -doped films. XMCD, measured in surfacesensitive total-electron-yield detection, gives µ eff = 4.2 µ B /Dy. The large measured moments make Dy-doped films interesting TI systems in which the TRS may be broken via the proximity effect due to an adjacent ferromagnetic insulator.

Study of Ho-doped Bi2Te3 topological insulator thin films

“…30 The surface morphology of the Ho-doped films was also further investigated by ex-situ measurements using scanning electron microscopy (SEM). Typical examples of large-and small-area scans, showing the characteristic triangular domain structure known from undoped and doped Bi 2 Te 3 thin films, 26 are shown in Figs. 1(a) and 1(b), respectively, for a film grown with T Ho ¼ 840 C. Compositional analysis was carried out using a combination of Rutherford backscattering spectroscopy (RBS) with 2.3 MeV He ions and particle induced x-ray emission (PIXE) with 1 MeV H ions.…”

“…2(a) reveals that the peaks shift toward lower diffraction angles and experience broadening as a function of doping concentration, which are consistent with observations for other MBE-grown RE-doped Bi 2 Te 3 thin films. 24,26,27 The appearance of these effects is indicative of an increased out-of-plane lattice constant and degradation in overall crystalline quality with increasing Ho doping. The expansion of the out-of-plane lattice parameter c, determined from the 2h values of the (0 0 l) peaks for 5 -65 using a nonlinear least-square cell-refinement program, 31 is plotted in Fig.…”

“…[24][25][26][27] In this letter, we present the MBE growth and a structural, magnetic, and electronic properties study of (Ho x Bi 1Àx ) 2 Te 3 topological insulator thin films, which aims to expand on the current understanding of the effects of RE doping in TIs.…”

“…In this sense, the Ho-doped films are comparable to the Gd-doped films, 28 but different than the Dy-doped films in which a gap has been observed, 27 despite the absence of magnetic long-range order. 26 Additional ARPES data are provided in the supplementary material. 30 In conclusion, we presented a systematic study of the structural, magnetic, and electronic properties of highquality MBE-grown (Ho x Bi 1Àx ) 2 Te 3 thin films.…”

Magnetic and magnetotransport properties of Bi2Se3 thin films doped by Eu

“…Although the properties of gapless interface states in the presence of magnetic impurities have been studied for more than 30 years ? , detailed investigation and explanation of the specific features of electron transport and of magnetic phenomena in 3D magnetic topological insulators remain an unresolved scientific problem even nowadays, being the subject of great interest 4,5 . We used Eu as magnetic impurity (J = 7/2) with the aim to study the effect of magnetic impurities on electron transport in 3D topological insulators.…”