Tunneling magnetoresistance has been observed in organic based spintronic devices using the organic semiconductors tetraphenyl porphyrin (TPP) and aluminum tris(8-hyroxyquinoline) (Alq3) as the spacer layer between La0.67Sr0.33MnO3 (LSMO) and Co films. The evidence for tunneling is twofold: (1) nonlinear current and conductance versus voltage curves and (2) an increasing junction resistance with decreasing temperature. In general, the magnetoresistance is found to decrease with increasing bias voltage and increasing temperature in both Alq3 and TPP junctions. These results demonstrate that organic molecules can form tunnel barriers that perform as well as most inorganic barrier materials on LSMO.

Carotenoids (Car), β-Carotene (I), 8′-apo-β-caroten-8′-al (II), and canthaxanthin (III), incorporated into activated Cu-MCM-41 were examined by UV/vis and EPR spectroscopies. A Cu 2+ -Car complex was formed for I and III but not for II. Formation of a complex results in distortion of the all-trans carotenoid geometry and a tetragonal geometry for Cu 2+ . The binding energies of Car and Cu 2+ , the changes in the maximum absorption, and the bond lengths of Car after the formation of the Cu 2+ -Car complex were examined by semiempirical ZINDO/1 and ZINDO/S calculations. Formation of a complex between Car and Cu 2+ favors both forward and back electron transfer (ET) reactions due to the short distance (∼2 Å) between Car and Cu 2+ , and reversible ET appears upon temperature cycling.

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Carefully tailored Fe/Cr epitaxial superlattices with extremely thin Fe layers have been grown on MgO(100) by molecular beam epitaxy. The low-angle x-ray spectra reveal the presence of sharp interfaces down to an Fe layer thickness of a few monolayers. An [Fe(4.5 Å)/Cr(12 Å)]50 superlattice shows a 220% magnetoresistance at 1.5 K, and a saturation field of 110 kOe. A further decrease of the Fe layer thickness produces a drastic decrease in the magnetoresistance.