Atomic level structural and chemical analysis of Cr-doped Bi₂Se₃
Scientific Reports Nature Publishing Group 6 (2016) 26549
Abstract:
We present a study of the structure and chemical composition of the Cr-doped 3D topological insulator Bi2Se3. Single-crystalline thin films were grown by molecular beam epitaxy on Al2O3 (0001), and their structural and chemical properties determined on an atomic level by aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy. A regular quintuple layer stacking of the Bi2Se3 film is found, with the exception of the first several atomic layers in the initial growth. The spectroscopy data give direct evidence that Cr is preferentially substituting for Bi in the Bi2Se3 host. We also show that Cr has a tendency to segregate at internal grain boundaries of the Bi2Se3 film.Magnetic ordering in Ho-doped Bi2Te3 topological insulator thin films
Physica Status Solidi: Rapid Research Letters Wiley 10:6 (2016) 467-470
Abstract:
We investigate the magnetic properties of Ho-doped Bi2Te3 thin films grown by molecular beam epitaxy. Analysis of the polarized x-ray absorption spectra at the Ho M5 absorption edge gives an effective 4f magnetic moment which is ~45% of the Hund's rule ground state value. X-ray magnetic circular dichroism (XMCD) shows no significant anisotropy, which suggests that the reduced spin moment is not due to the crystal field effects, but rather the presence of non-magnetic or antiferromagnetic Ho sites. Extrapolating the temperature dependence of the XMCD measured in total electron yield and fluorescence yield mode in a field of 7 T gives a Curie-Weiss temperature of \theta_CW ~ -30 K, which suggests antiferromagnetic ordering, in contrast to the paramagnetic behavior observed with SQUID magnetometry. From the anomaly of the XMCD signal at low temperatures, a Neel temperature TN between 10 K and 25 K is estimated.On the temperature dependence of spin pumping in ferromagnet–topological insulator–ferromagnet spin valves
Results in Physics Elsevier 6 (2016) 293-294
Abstract:
Topological insulators (TIs) have a large potential for spintronics devices owing to their spinpolarized, counter-propagating surface states. Recently, we have investigated spin pumping in a ferromagnet-TI-ferromagnet structure at room temperature. Here, we present the temperature-dependent measurement of spin pumping down to 10 K, which shows no variation with temperature.Transverse field muon-spin rotation measurement of the topological anomaly in a thin film of MnSi
Physical Review B: Condensed Matter and Materials Physics American Physical Society 93:14 (2016) 140412(R)
Abstract:
We present the results of transverse-field muon-spin rotation measurements on an epitaxially grown 40-nm-thick film of MnSi on Si(111) in the region of the field-temperature phase diagram where a skyrmion phase has been observed in the bulk. We identify changes in the quasistatic magnetic field distribution sampled by the muon, along with evidence for magnetic transitions around T≈40 and 30 K. Our results suggest that the cone phase is not the only magnetic texture realized in film samples for out-of-plane fields.
‘Chiral damping of field driven magnetic domain walls’
Nature Materials, 15, 272-277 (2016).