Roger H. Koch

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Time-resolved measurements of spin-transfer-induced (STI) magnetization reversal were made in current-perpendicular spin-valve nanomagnetic junctions subject to a pulsed current bias. These results can be understood within the framework of a Landau-Lifshitz-Gilbert equation that includes STI corrections and a Langevin random field for finite temperature.(More)
We propose a model for 1/f flux noise in superconducting devices (f is frequency). The noise is generated by the magnetic moments of electrons in defect states which they occupy for a wide distribution of times before escaping. A trapped electron occupies one of the two Kramers-degenerate ground states, between which the transition rate is negligible at low(More)
Current-induced magnetization dynamics in Co/Cu/Co trilayer nanopillars (approximately 100 nm in diameter) have been studied experimentally at low temperatures for large applied fields perpendicular to the layers. At 4.2 K an abrupt and hysteretic increase in resistance is observed at high current densities for one polarity of the current, comparable to the(More)
Current-induced excitations in Cu/Co/Cu single ferromagnetic layer nanopillars ( approximately 50 nm in diameter) have been studied experimentally as a function of Co layer thickness at low temperatures for large applied fields perpendicular to the layers. For asymmetric junctions current-induced excitations are observed at high current densities for only(More)
We present a multi-level quantum theory of decoherence for a general circuit realization of a superconducting qubit. Using electrical network graph theory, we derive a Hamiltonian for the circuit. The dissipative circuit elements (external impedances, shunt resistors) are described using the Caldeira-Leggett model. The master equation for the(More)
A direct probe of superparamagnetism was used to determine the complete anisotropy energy distribution of Co nanoparticle films. The films were composed of self-assembled lattices of uniform Co nanoparticles of 3 or 5 nm in diameter, and a variable temperature scanning-SQUID microscope was used to measure temperature-induced spontaneous magnetic noise in(More)
The use of accelerator hardware for micromagnetics simulations is described, along with some initial results. The accelerator calculates the dipole interactions at 400 gigaflops, allowing large simulations to be performed with arbitrary geometries. Two research programs are highlighted, the simulation of a curved MRAM cell and the simulation of the write(More)
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