Professor Stephen Blundell

Abstract:

Although the coexistence of superconductivity and ferromagnetism in one compound is rare, some examples of such materials are known to exist. Methods to physically prepare hybrid structures with both competing phases are also known, which rely on the nanofabrication of alternating conducting layers. Chemical methods of building up hybrid materials with organic molecules (superconducting layers) and metal complexes (magnetic layers) have provided examples of superconductivity with some magnetic properties, but not fully ordered. Now, we report a chemical design strategy that uses the self assembly in solution of macromolecular nanosheet building blocks to engineer the coexistence of superconductivity and magnetism in [Ni(0.66)Al(0.33)(OH)(2)][TaS(2)] at ∼4 K. The method is further demonstrated in the isostructural [Ni(0.66)Fe(0.33)(OH)(2)][TaS(2)], in which the magnetic ordering is shifted from 4 K to 16 K.

Abstract:

We show that the quasi-one-dimensional organic ferromagnet 2-benzimidazolyl nitronyl nitroxide (2-BIMNN) undergoes a phase transition to long-range magnetic order below TC =1.0 (1) K. The intrachain exchange interactions are J/kB =22 K and so the low-temperature ordering demonstrates the weakness of the interchain interactions. Our electron-spin-resonance measurements provide further evidence for the one-dimensional character of the magnetic fluctuations in 2-BIMNN and, using muon-spin rotation, we are able to characterize the broad phase transition in the material. We discuss these results in the context of other spin- 1 2 quasi-one-dimensional Heisenberg ferromagnets and demonstrate that 2-BIMNN is the best realization of a one-dimensional Heisenberg ferromagnet among purely organic compounds yet discovered. © 2010 The American Physical Society.