Magnetically doped topological insulators enable the quantum anomalous Hall effect (QAHE) which provides quantized edge states for lossless charge transport applications [1][2][3][4][5][6][7][8][9]. The edge states are hosted by a magnetic energy gap at the Dirac point[2] but all attempts to observe it directly have been unsuccessful. The size of this gap is considered the clue to overcoming the present limitations of the QAHE, which so far occurs only at temperatures one to two orders of magnitude below its principle limit set by the ferromagnetic Curie temperature T C [8,9]. Here, we use low temperature photoelectron spectroscopy to unambiguously reveal the magnetic gap of Mn-doped Bi 2 Te 3 films which is present only below T C . Surprisingly, the gap turns out to be ∼ 90 meV wide, which not only exceeds k B T at room temperature but is also 5 times larger than predicted by density functional theory [10]. By an exhaustive multiscale structure characterization we show that this enhancement is due to a remarkable structure modification induced by Mn doping. Instead of a disordered impurity system, it forms an alternating sequence of septuple and quintuple layer blocks, where Mn is predominantly incorporated in the center of the septuple layers. This self-organized heterostructure substantially enhances the wave-function overlap and the size of the magnetic gap at the Dirac point, as recently predicted [11]. Mn-doped Bi 2 Se 3 forms a similar heterostructure, however, only a large, albeit nonmagnetic gap is formed. We explain both differences based on the higher spin-orbit interaction in Bi 2 Te 3 with the most important consequence of a magnetic anisotropy perpendicular to the films, whereas for Bi 2 Se 3 the spin-orbit interaction it is too weak to overcome the dipole-dipole interaction. Our findings provide crucial insights for pushing the lossless transport properties of topological insulators towards room-temperature applications.We thank B. Henne, F. Wilhelm, and A. Rogalev for support of the XANES and EX-AFS measurements at ID 12 and BM23 beam lines of the ESRF, V. Holý for advices on the structure model, W. Grafeneder for the TEM sample preparation and G. Bihlmayer and A. Ernst for helpful discussions. S.A.K and J.M. are grateful for support from CEDAMNF (CZ.02.1.01/0.0/0.0/15 003/0000358) of Czech ministry MSMT.

This study reports first synthesis of MXene-derived co-existing phases. New family of two-dimensional materials such as Ti3C2 namely MXene, having transition metal forming hexagonal structure with carbon atoms have attracted tremendous interest now a days. We have reported structural, optical and magnetic properties of undoped and La-doped Ti3C2Tx MXene synthesized using co-precipitation method. The c-lattice parameters (c-LP) calculated for La-MXene is c=18.3Å which is slightly different from the parent un-doped MXene (c=19.2Å), calculated from X-ray diffraction data. The doping of La +3 ions shrinks Ti3C2Tx layers perpendicular to the planes but expands slightly the in-plane lattice parameters. The band gap for MXene is calculated to be 1.06 eV which is increased to 1.44 eV after the doping of La +3 ion that shows its good semiconducting nature. The experimental results for magnetic properties of both the samples have been presented and discussed, indicating the presence of ferromagnetic-antiferromagnetic phases co-existing. The results presented here are unique and first report on magnetic properties of two-dimensional carbides for magnetic data storage applications.

To get a reliable ab-initio value for the magneto-crystalline anisotropy (MCA) energy of FePt, we employ the full-potential linearized augmented plane wave (FLAPW) method and the full-potential Korringa-Kohn-Rostoker (KKR) Green function method. The MCA energies calculated by both methods are in a good agreement with each other. As the calculated MCA energy significantly differs from experiment, it is clear that many-body effects beyond the local density approximation are essential. It is not really important whether relativistic effects for FePt are accounted for by solving the full Dirac equation or whether the spin-orbit coupling (SOC) is treated as a correction to the scalar-relativistic Hamiltonian. From the analysis of the dependence of the MCA energy on the magnetization angle and on the SOC strength it follows that the main mechanism of MCA in FePt can be described within second order perturbation theory. However, a distinct contribution not accountable for by second order perturbation theory is present as well.

The thermoelectric properties of pristine graphene and H 2 S adsorbed onto bridge, hollow and top sites of a graphene sheet are investigated using the semi-classical Boltzmann transport theory. The average values of electrical conductivity, thermal conductivity, Seebeck coefficient, figure of merit (ZT) and the average value of the power factor (P av ) are reported and discussed in detail. While pristine graphene is a zero band gap semiconductor, adsorption of H 2 S onto the bridge site opens up a direct energy gap of about 0.04 eV, adsorption of a H 2 S molecule onto the top site opens up a gap of 0.3 eV, and adsorption of H 2 S onto the hollow site makes it metallic. The investigation of ZT and power factor values suggests that a top-site configuration could be a potential candidate for thermoelectric applications in the range 300-600 K.

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