Self-Assembled Nanoparticle Array for Spintronics and

1. Self-Assembled Nanoparticle Array for Spintronics and High Frequency MaterialsDMR-0547036 PI:Hao Zeng MR as a function of field for samples annealed at (a) 400 C and (b) 600 C; points are experimental data and lines are fitting curves using where L is Langevin function, =NB/kT. The experiential data are accurately fitted by this function. • We have combined self-assembly with photolithography to fabricate charge transport devices incorporating 3D arrays of monodisperse half-metallic magnetite (Fe3O4) nanoparticles. We have discovered a ubiquitous magnetoresistance (MR) behavior: MR for all samples shows strong high field dependence, despite the magnetization being nearly saturated. We have developed a model based on non-collinear spins at the nanoparticle surfaces. Langevin-like functions derived from the model yields excellent fit for all MR vs. field curves. [Phys. Rev. B. 76 (2007)] • We have observed strong reduction of magnetization in FePt nanoparticles. We have shown that it is an intrinsic effect for materials with competing interactions. We have constructed a model based purely on geometrical constraints: broken symmetry and missing nearest neighbors leading to preferential AFM order for certain surface terminations. The predictions of an unconventional temperature dependence of magnetization and existence of a magnetically “dead layer” are consistent with experimental results. The outcome has strong implications in future applications of magnetic nanoparticles for bio-medical and data storage fields. (a) Monte Carlo simulation of magnetization vs. temperature for a nanoparticle with 1297 atoms, R is the ratio of nearest neighbor/second nearest neighbor exchange parameters; (b) Measured M vs. T for 3 nm FePt nanoparticles.

2. Self-Assembled Nanoparticle Array for Spintronics and High Frequency MaterialsDMR-0547036 PI:Hao Zeng • Undergraduate and high school research: A number of undergraduate and high school students have been involved in various research projects in the PI’s lab. Two of them are from underrepresented groups. • Undergraduate student seminar: The PI participated in UB UE141 Freshman Seminar Series. This program offers a small class experience for first-year students, providing them with the opportunity to engage with faculty members in a congenial, academic setting. The PI gave a lecture on the growth of nanoparticles with chemical routes. This semester, the PI is again participating in CAS 101, representing the Physics Department. This class is a series of lectures presented by faculty in the College of Arts and Sciences who deliver exciting and informative lectures on their discipline and research interests. • Outreach program: The PI has targeted the Native American Magnet School for his outreach efforts. This is a K-8 middle school with 90 percent of its students being minorities and living at or below the poverty level. The PI gave a lecture/ demonstration of electric charge and electricity using a Van de Graaff generator. The students were thrilled by the demonstration. A selected group from grade 8 were given a guided tour of the “Physics and Arts” exhibition located in the physics department, where they were shown a Foucault pendulum, a camera obscura, a plasma ball, a spectrometer and some antique instrumentation. Charlyn Meredith demonstrating the making of nanoporous alumina templates in our lab. A poster-sized card from students at Buffalo Native American School 19