Abstract
Integrating nanocrystals (NCs) into magnetic tunnel structures is of considerable interest due to expectation of novel properties from their spin selective transport and single electron features. Superstructures by colloidal NCs having translational and orientational order and interesting collective magnetic properties can be prepd. by soln. casting through sensitive interparticle and particle-substrate interactions. In this work, we discuss the study on magnetic field induced assembly of mono-dispersed iron oxide NCs to obtain spin filter effect across the superlattice array, when sandwiched between gold electrodes. The deposition of mixed phase Fe3O4@γ-Fe2O3 NCs on SiO2/Au surface proceeds through slow solvent evapn. and are studied for controlled interparticle spacing. For specific NC concn., the ordering depends on the substrate chem. and the ligands passivating NC surface, which affects the concn. of cluster nuclei formed. In presence of a magnetic field, the tunnel structure exhibits enhanced pos. tunnel magnetoresistance at low temps., which could be related to their ferromagnetism and the attempts by electrons to percolate NC superlattice with preserved spin. A sign reversal for magnetoresistance is exhibited by the vertical tunnel junctions on raising the temp.
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