Tuning magnetism and superconductivity in nickel- and cobalt- based chalcogenides Ludmila Babicova, Prof Simon Clarke University of Oxford, UK The discovery of high-temperature superconductivity in La(O,F)FeAs has sparked renewed interest in intermetallics bearing the square anti-fluorite layers of M 2 X 2 (M = transition metal, X = pnictide or chalcogenide), since this is where superconductivity is believed to occur.The tetragonal FeSe, composed of anti-fluorite layers of Fe 2 Se 2 , has been found to be superconducting at 8K.Upon insertion of an alkali metal into this structure, a new phase – A Fe 2 Se 2 – emerges, with an increased superconducting transition temperature of 30K. A Fe 2 Se 2 belongs to the 122 family of iron-based superconductors, adapting a versatile ThCr 2 Si 2 -type structure, which has been known to demonstrate interesting magnetic phenomena.In this research, we are exploring the magnetic regions of nickel and cobalt-based 122 phases, which adapt the ThCr 2 Si 2 -type structure. The solid solutions of KNi 2-x Co x Se 2 and RbNi 2-x Co x Se 2 are both particularly interesting in terms of the magnetic states present in the members of their respective members; KNi 2 Se 2 is superconducting, while KCo 2 Se 2 is ferromagnetic, and the middle member – KNiCoSe 2 – shows antiferromagnetic behaviour. RbNi 2 Se 2 is a new, unreported phase and is an antiferromagnet, while RbNiCoSe 2 and RbCo 2 Se 2 are both ferromagnets. Therefore, our study shows the tuning of magnetism as a function of composition across the solid solution series of KNi 2-x Co x Se 2 and RbNi 2-x Co x Se 2 . References 1. Shatruk, M. Solid State Chem. Soc. 2019 , 272 , 198-209 2. Zhou, G. et al. 2016 , Appl. Phys. Lett. 108 . 3. Neilson, J. R., McQueen, T. M., Llobet, A., Wen, J. & Suchomel, M. R. Phys. Rev. B - Condens. Matter Mater. Phys. 2013 , 87 , 1–11. 4. Lei, H. et al. 2014 , J. Phys. Condens. Matter 26 . 5. Zhang, P. & Zhai, H. F., 2017 , Condens. Matter 2 , 1–14
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