Electron spin-polarized tunneling is observed through an ultrathin layer of the molecular organic semiconductor tris(8-hydroxyquinolinato)aluminum (Alq3). Significant tunnel magnetoresistance (TMR) was measured in a Co/Al2O3/Alq3/NiFe magnetic tunnel junction at room temperature, which increased when cooled to low temperatures. Tunneling characteristics, such as the current-voltage behavior and temperature and bias dependence of the TMR, show the good quality of the organic tunnel barrier. Spin polarization (P) of the tunnel current through the Alq3 layer, directly measured using superconducting Al as the spin detector, shows that minimizing formation of an interfacial dipole layer between the metal electrode and organic barrier significantly improves spin transport.

A three-dimensional (3D) ordered superlattice of colloidal iron oxide nanocrystals obtained by magnetic-field-assisted self-assembly has been studied by grazing incidence small-angle X-ray scattering (GISAXS). A new model to simulate and interpret GISAXS patterns is presented, which returns the structural and morphological details of 3D nanocrystal-built supercrystals. The model is applied to a sample with a suitable surface morphology, allowing the observation of "volume diffraction" even at extremely low grazing incidence angle. In this particular case, the average fcc-like stacking of the nanocrystals (building blocks), their spherical shape, and statistical information on their size distribution and positions within the superlattice have been safely deduced. The proposed model is expected to be amendable for the analysis of more complex structures and applicable to a large variety of nanocrystal-based assemblies.

Magnetic tunnel junctions sandwiching a superlattice thin film of iron oxide nanocrystals (NCs) have been investigated. The transport was found to be controlled by Coulomb blockade and single-electron tunneling, already at room temperature. A good correlation was identified to hold between the tunnel magnetoresistance (TMR), the expected magnetic properties of the NC arrays, the charging energies evaluated from current-voltage curves, and the temperature dependence of the junction resistance. Notably, for the first time, a switching from negative to positive TMR was observed across the Verwey transition, with a strong enhancement of TMR at low temperatures.

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