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Author: Kasinathan, D. × Has files: Yes ×

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    Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1 +yTe
    (Washington : National Academy of Sciences, 2019) Rößler, S.; Koz, C.; Wang, Z.; Skourski, Y.; Doerr, M.; Kasinathan, D.; Rosner, H.; Schmidt, M.; Schwarz, U.; Rößler, U.K.; Wirth, S.
    A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state.
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    Charge-transfer energy in iridates: A hard x-ray photoelectron spectroscopy study
    (College Park, ML : American Physical Society, 2020) Takegami, D.; Kasinathan, D.; Wolff, K.K.; Altendorf, S.G.; Chang, C.F.; Hoefer, K.; Melendez-Sans, A.; Utsumi, Y.; Meneghin, F.; Ha, T.D.; Yen, C.H.; Chen, K.; Kuo, C.Y.; Liao, Y.F.; Tsuei, K.D.; Morrow, R.; Wurmehl, S.; Büchner, B.; Prasad, B.E.; Jansen, M.; Komarek, A.C.; Hansmann, P.; Tjeng, L.H.
    We have investigated the electronic structure of iridates in the double perovskite crystal structure containing either Ir4+ or Ir5+ using hard x-ray photoelectron spectroscopy. The experimental valence band spectra can be well reproduced using tight-binding calculations including only the Ir 5d, O 2p, and O 2s orbitals with parameters based on the downfolding of the density-functional band structure results. We found that, regardless of the A and B cations, the A2BIrO6 iridates have essentially zero O 2p to Ir 5d charge-transfer energies. Hence double perovskite iridates turn out to be extremely covalent systems with the consequence being that the magnetic exchange interactions become very long ranged, thereby hampering the materialization of the long-sought Kitaev physics. Nevertheless, it still would be possible to realize a spin-liquid system using the iridates with a proper tuning of the various competing exchange interactions.