Gaining control of the building blocks of magnetic materials and thereby achieving particular characteristics will make possible the design and growth of bespoke magnetic (nano)devices. The advent of molecular materials, and especially coordination polymers, represents a significant step towards this goal, allowing magnetic centres (Ni, Cu, Cr, Mn etc.) to be arranged on a variety of crystalline frameworks. In this way, diverse magnetic materials with many different effective dimensionalities, anisotropies and other properties can be synthesized. Magnetization (M) measurements in very high magnetic fields H have an important role to play in such work. The characteristic shape of the M(H) curve can in many cases be modelled to extract the effective dimensionality of the magnet in question. Moreover, the magnetic fields at which features in M(H) occur give accurate values of the various quantum energies. The talk will illustrate various “molecular architecture” strategies, including the use of chemical pressure via space-filling counter-ions, isotopic substitution, and judicious alteration of synthesis conditions. These techniques allow the effective dimensionality and sizes of various interactions to be adjusted almost at will, as evidenced in measurements using magnetic fields of up to 95 T, along with complementary neutron-scattering and thermal experiments, plus numerical models. Our experiments show that many of the resulting materials are “model” systems that allow fundamental physics problems to be studied. As an example, quasi-one-dimensional spin-1 antiferromagnetic chains, in which the relative sizes of the single-ion anisotropy (D) and the intrachain (J) and interchain (J0) exchange interactions can be varied, will be described. This will allow three competing phases - a Haldane gapped phase, a quantum paramagnet and an XY-ordered state, with a quantum critical point at their junction – to be explored using convenient laboratory conditions.

High-magnetic-field explorations of molecular architecture and fundamental physics in organic quantum magnets

2019 Spring National Meeting

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