Layered magnetic molecular-frameworks
Mon, Jul 20, 2020
Figure: Structure and magnetic properties of the magnetic molecular frameworks M(NCS)2 (M = Mn, Fe, Co, Ni). Left: the chemical structure of the M(NCS)2 frameworks; centre: the net magnetic interaction strength for each framework and right: the magnetic structures of M(NCS)2, with arrows denoting the relative orientation of the bar magnets. The magnetic structures of Mn(NCS)2, Fe(NCS)2 and Co(NCS)2 are in orange, and in blue for Ni(NCS)2.
A team at the University of Nottingham, University of Cambridge and ISIS Neutron and Muon Source have shown that a family of new molecular framework have intriguing magnetic properties.
Layered magnetic materials are an important class of compounds. The structures of these materials comprise sheets of magnetic metal atoms connected to one another typically via “linker” atoms, such as oxygen, sulphur, or iodine. Each magnetic metal atom can be conceptualised as an individual bar magnet, or spin, whose orientation (‘up’ or ‘down’) can be switched using an external magnetic field. The ease with which the orientation of the bar magnets can be flipped depends on the strength of the interactions between a metal atom and its neighbours. One potential application of these layered magnetic materials is in data-storage devices, where the orientation of individual spins (up or down) is encoded as a string of binary 1’s and 0’s. The strength of magnetic interactions in these materials can be influenced by the identity of both the metal and the linker.
When the linker atoms are instead replaced with by linker molecules, new kinds of magnetic layered materials “molecular framework” can be generated. We have previously demonstrated that thiocyanate, (NCS)–, is a molecule which can convey strong magnetic interactions between metal atoms, but to date, very few layered magnetic thiocyanate frameworks have been studied. We therefore decided to synthesise a series of these frameworks with the general formula M(NCS)2—where M = Mn, Fe, Co, Ni—and undertake a systematic investigation of their magnetic properties. We found that the strength of magnetic interactions can be significantly increased by using ‘earlier’ metals (i.e.X Mn and Fe). We also discovered that the spins metal atoms in Ni(NCS)2 align so that all atoms have the same orientation, giving a net non-zero magnetisation in each layer. This suggests that by delaminating Ni(NCS)2, a single-layer magnet may be constructed, which could be a candidate memory storage material for use in devices.
Paper
E N Bassey, J A M Paddison, E N Keyzer, J Lee, P Manuel, I da Silva, S E Dutton, C P Grey, M J Cliffe
Inorg. Chem., 59, 11627 (2020).