Magnetism and Charge Transport in Nanoparticle Arrays Hao Zeng, SUNY at Buffalo, DMR 0547036

1. Magnetism and Charge Transport in Nanoparticle ArraysHao Zeng, SUNY at Buffalo, DMR 0547036 • Surface Magnetization Reversal Modes in Nanoparticles — We have shown earlier that for systems with competing exchange interactions, the symmetry of the surface termination can lead to reduction and an unusual temperature dependence of magnetization, and a possible independent surface magnetization reversal mode. In this work, we show direct evidence of such surface reversal mode using magnetic second harmonic generation (MSHG) measurements. The surface sensitivity of MSHG make it a unique technique to probe surface magnetism. • Charge transport properties of self-assembled Co nanoparticle arrays with a natural oxide surface have been studied. Resistance shows thermally activated behavior. A giant positive magnetoresistance of 1400% is observed. The positive MR and most of its features can be explained by the Zeeman splitting of the localized states that suppresses the spin dependent hopping paths (J. Appl. Phys. 105, 063920 (2009)). (c) Fig.1 Magnetic hysteresis measured by (a) MOKE and (b) MSHG; (c) Simulated spin configuration of a model nanoparticle. Fig.2 (a) ln(R(H)/R(0)) as a function of magnetic field (b) ln(R(H)/R(0)) as a function of H/T2 ; all curves collapse onto a single curve at low fields.

2. Mentoring of High School and Undergraduate StudentsHao Zeng, SUNY at Buffalo, DMR 0547036 The PI continues to mentor high school students who participated in summer research projects in his lab. Shown in the pictures are Davion Currie and Brendan Hughes, both local high school students. Davion working with graduate student Chaehyun Kim on electrochemcial synthesis of nanoporous arrays. Brendan working on assembling a nanocomposite solar cell for photocurrent measurements. Davion presenting his research to a group of faculty and fellow high school students.