Abstract
The magnetic, structural, conductivity and magnetoresistance properties of [Ni(quinoline-8-selenoate)2] ([Ni(qs)2]) have been studied. Despite the insolubility of the material necessitating its study as a powdered sample, a remarkably high conductivity has been measured. The conductivity is an order of magnitude greater than the thin-film processable thiol analogue previously reported and has been interpreted through the same space-charge limited conduction mechanism with charges injected from the electrodes. The introduction of selenium, results in a material with conductivity approaching metallic due to the enhanced interaction between adjacent molecules. Additionally, under an applied magnetic field, the material displays a negative magnetoresistance effect above 35% at 2 K. The effect can still be observed at 200 K and is interpreted in terms of a double-exchange mechanism.
Highlights
Molecular electronics, encompassing the use of small molecules or polymers for use as conductors and semiconductors, has seen an incredible expansion in research, both academically and industrially, over a relatively short period of time
A controllable giant negative magnetoresistance (GNMR) of up to 95% was achieved, using magnetic fields up to 15 Tesla
In an effort to further explore and improve the intrinsic magnetoresistive effect observed in the [Ni(qt)2] material we have studied the selenium analogue, Ni(quinolone-8selenoate)2, [Ni(qs)2] (Fig. 1b)
Summary
Molecular electronics, encompassing the use of small molecules or polymers for use as conductors and semiconductors, has seen an incredible expansion in research, both academically and industrially, over a relatively short period of time. The most common method of incorporating molecular materials utilises non-magnetic organic spacers between ferromagnetic materials in a spin valve.[11,15,16] This approach is, hampered by difficult interface engineering.[17,18,19] Magnetoresistance has been observed in organic diode arrangements employing a thin film of molecular semiconductor, the interpretation is still controversial and the sign of the effect changes with experimental conditions.[20] A appealing alternative is utilising the intrinsic GMR possible in a film of paramagnetic molecular materials This approach has previously been used to generate negative MR up to 95% and relies upon a well-understood double-exchange mechanism, but has so far been limited to very few classes of molecule.[21,22,23] ([TPP]Dicyano(phthalocyaninato)iron)[2] was the first material of its type to be examined for the relationship between molecular magnetism and charge transport.[23,24] A controllable giant negative magnetoresistance (GNMR) of up to 95% was achieved, using magnetic fields up to 15 Tesla. Sulfur and selenium have similar chemical properties the larger selenium atom has more diffuse orbitals and so it was hypothesised that replacement of S with Se would increase orbital overlap and intermolecular interactions enhancing the previously observed effects
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