Filters

2019 - 201912020 - 20231

More filters

2020 - 20242
Reset filters

Settings

Subject: chemical analysis × Subject: phase transition × WGL Institute: IFWD ×

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Resonating holes vs molecular spin-orbit coupled states in group-5 lacunar spinels
    ([London] : Nature Publishing Group UK, 2023) Petersen, Thorben; Bhattacharyya, Pritam; Rößler, Ulrich K.; Hozoi, Liviu
    The valence electronic structure of magnetic centers is one of the factors that determines the characteristics of a magnet. This may refer to orbital degeneracy, as for jeff = 1/2 Kitaev magnets, or near-degeneracy, e.g., involving the third and fourth shells in cuprate superconductors. Here we explore the inner structure of magnetic moments in group-5 lacunar spinels, fascinating materials featuring multisite magnetic units in the form of tetrahedral tetramers. Our quantum chemical analysis reveals a very colorful landscape, much richer than the single-electron, single-configuration description applied so far to all group-5 GaM4X8 chalcogenides, and clarifies the basic multiorbital correlations on M4 tetrahedral clusters: while for V strong correlations yield a wave-function that can be well described in terms of four V4+V3+V3+V3+ resonant valence structures, for Nb and Ta a picture of dressed molecular-orbital jeff = 3/2 entities is more appropriate. These internal degrees of freedom likely shape vibronic couplings, phase transitions, and the magneto-electric properties in each of these systems.
  • Thumbnail Image
    Item
    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.