Ghazanfari, M.R.; Santhosh, A.; Siemensmeyer, K.; Fuß, F.; Staab, L.; Vrijmoed, J.C.; Peters, B.; Liesegang, M.; Dehnen, S.; Oeckler, O.; Jerabek, P.; Thiele, G.: Large Exchange Bias, High Dielectric Constant, and Outstanding Ionic Conductivity in a Single-Phase Spin Glass. Advanced Electronic Materials 8 (2022), p. 2200483/1-10
10.1002/aelm.202200483
Open Access Version
Abstract:
The multigram synthesis of K [Fe S ] starting from K S and FeS is presented, and its electronic and magnetic properties are investigated. The title compound obtains a defect variant of the K[Fe Se ] structure type. Dielectric and impedance measurements indicate a dielectric constant of 1120 at 1 kHz and an outstanding ionic conductivity of 24.37 mS cm at 295 K, which is in the range of the highest reported value for potential solid-state electrolytes for potassium-ion batteries. The Seebeck coeffcient of the n-type conductor amounts to −60 μV K at 973 K. The mismatch of the measured electrical resistivity and the predicted metal-like band structure by periodic quantum chemical calculations indicates Mott insulating behavior. Magnetometry demonstrates temperature-dependent, large exchange biasfields of 35 mT, as a consequence of the coexistence of spin glass and antiferromagnetic orderings due to the iron vacancies in the lattice. In addition, the decreasing training effects of 34% in the exchange bias are identified at temperatures lower than 20 K. These results demonstrate the critical role of iron vacancies in tuning the electronic and magnetic properties and a multifunctional material from abundant and accessible elements.