Fe4Si2Sn7O16 : a “Partial” Spin-liquid Candidate on a Kagomé Lattice

Orateur : Christopher D. LING (University of Sydney, Australia)

The compound Fe4Si2Sn7O16 has a unique crystal structure, consisting of ionic oxide layers based on edge-sharing FeO6 and Sn4+O6 octahedra alternating with layers of intermetallic character based on FeSn2+6 octahedra, separated by covalent SiO4 tetrahedra. [1,2] The ionic layers contain kagomé lattices of magnetic Fe2+ cations (octahedral crystal field, high-spin [HS] d6, S = 2) with perfect trigonal symmetry ; while the intermetallic “stannide” layers contain non-magnetic low-spin [LS] Fe2+ (S = 0). The formula is more correctly written as FeFe3Si2Sn7O16 to differentiate the one LS-Fe2+ per formula unit in the intermetallic layer from the three HS-Fe2+ per formula unit in the kagomé oxide layer. Fe4Si2Sn7O16 also has a unique magnetic ground state below a Néel ordering temperature TN = 3.5 K, in which the spins on 2/3 of the Fe2+ sites in the kagomé oxide layers order antiferromagnetically, while 1/3 remain disordered and fluctuating down to at least 0.1 K. [3] In this talk I will discuss the nature and origins of this “striped” partial spin-liquid state, which has not been observed experimentally nor explicitly predicted theoretically to the best of our knowledge, and possible ways in which its chemistry and physics could be extended.

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