Derivation of Novel Magnetic Layered Compounds
Eteri Svanidze, Tiglet Besara, M. Fevsi Ozaydin, Chandra Sekhar Tiwary, Jiakui K. Wang, Sruthi Radhakrishnan, Sendurai Mani, Yan Xin, Ke Han, Hong Liang, Theo Siegrist, Pulickel M. Ajayan, E. Morosan, "High hardness in the biocompatible intermetallic compound β-Ti3Au" Sci. Adv. 2, e1600319 (2016)
A. Marcinkova, J. K. Wang, C. Slavonic, Andriy H. Nevidomskyy, K. F. Kelly, Y. Filinchuk, and E. Morosan "Topological metal behavior in GeBi2Te4 single crystals" Phys. Rev. B 88, 165128 (2013)
Layered inorganic compounds have garnered much attention since the discovery of high-temperature superconducting perovskites. The physical properties of layered compounds like these have been shown to be highly sensitive to changes in structure and composition. Two such compounds—Sr2Mn3As2O2 and Sr2F2Fe2OS2—are well-characterized antiferromagnets with pseudo-2D spin structures; by altering their compositions via atomic substitution, we can generate a series of related compounds to study the relationship between the composition and the magnetic properties of these materials. Ultimately, by substitution we hope to be able to change the fundamental spin structures of the parent compounds from two-dimensional to three-dimensional and probe new physical behaviors resulting from this change.
Hard biocompatible alloys
Ti-Au alloys revealed surprising mechanical properties, with the hardness varying non-monotonously with the relative Ti:Au ratio. For a particular composition of 25% Au, corresponding to the compound β-Ti3Au, the hardness is maximum, and about four times larger then that of some steels. Additionally, some other traits of this particular compound (reduced coefficient of friction and wear rates, high biocompatibility) make it promising for medical applications.
Topological metal GeBi2Te4
Topological systems have recently emerged as a novel electronic state of quantum matter, with a lot of focus on topological insulators (TIs). TIs are materials that, in the bulk, are akin to ordinary insulators and have a band gap. However the edge (for two dimensional materials) or surface (for three-dimensional materials) states are gapless spin-polarized states which are topologically protected, or are stable against local perturbations and arise due to time-reversal symmetry.
In this pseudo-binary compound (GeTe-Bi2Te3 [GBT]) crystallographic analysis revealed a small distortion of the Ge octahedra with significant impact on the Fermi surface topology. As a consequence, the contradiction between experiment and theory related to the Dirac point in this compound was resolved. It had been predicted theoretically that a Dirac cone would occur below the Fermi energy, while experimentally (ARPES measurements) this feature was observed exactly at EF. The corrected (distorted) crystal structure confirmed the ARPES results, while indicating that GBT is likely a topological metal instead of a topological insulator.