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SFB 1170

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SFB Extra Seminar

"Crystal growth and magnetic property study of honeycomb material A2TO3 (A = Na, Li and T = Ir, Ru) and study of electron spin resonance (ESR) spectroscopy of MnBi4Te7 "
Datum: 09.12.2019, 14:15 - 15:45 Uhr
Kategorie: Seminar
Ort: Hubland Süd, Geb. P1 (Physik), E 136
Veranstalter: SFB 1170 ToCoTronics
Vortragende: Dr. Kavita Mehlawat -Leibniz Institute for Solid State and Materials Research Dresden

Kitaev-like bond-directional exchange interactions are novel and quite different from the ubiquitous Heisenberg interactions found in most magnets. These kinds of interactions open up new possibilities in the exploration and designing of new quantum magnets which can host novel quantum ground states like spin-liquids. During my graduate work I have synthesized single crystals of A2TO3 (A = Na, Li and T = Ir, Ru) and studied their electrical transport, magnetic, and thermal properties. Our work provides several new results: (i) the first thermodynamic evidence of possible fictionalization of electrons in Na2IrO3 because of proximity to the Kitaev spin-liquid state, (ii) evidence through magnetic impurity doping, of fragile magnetic order and importance of nearest neighbour interactions and spin-orbit coupling in deciding the magnetic ground state in Na2IrO3, (iii) a novel method (reactive ion etching) of surface doping Na2IrO3 and possibly other layered oxides has been discovered. The surface conductivity of Na2IrO3 crystals could be increased by 11 orders of magnitude by varying etching times. The samples which turned metallic show transport anomalies consistent with charge density wave or structural instabilities, and (iv) First crystal growth of Li2RuO3 is reported where the crystals crystallize in the P21/m structure and show the expected high temperature magneto-structural transition.

The van der Waals compound MnBi4Te7 belongs to the family of (Bi2Te3)n(MnBi2Te4), (n = 0, 1, 2) heterostructures and is a candidate magnetic topological insulator. It is the first magnetic material that features both, the intrinsic net magnetization and a band inversion. Static magnetic susceptibility (????) and magnetization (M) measurements as a function of the applied field (H) on MnBi4Te7 single-crystals show an antiferromagnetic state at T???? = 13 K and a ferromagnetic-like hysteresis occurring upon cooling below 5 K. We performed electron spin resonance (ESR) spectroscopy measurements in wide frequency and temperature ranges to explore the dynamic magnetic properties of MnBi4Te7. From high-frequency ESR measurements, we obtain evidence that MnBi4Te7 is an easy-axis type ferromagnet and ferromagnetic spin correlations persist up to T = 30 K on the time scale of an ESR experiment (10-10- 10-11 s).

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