Evaluating Ovonic Threshold Switching Materials with Topological Constraint Theory.

The physical properties of ovonic threshold switching (OTS) materials are of great interest due to the use of OTS materials as selectors in cross-point array nonvolatile memory systems. Here, we show that the topological constraint theory (TCT) of chalcogenide glasses provides a robust framework to describe the physical properties of sputtered thin film OTS materials and electronic devices. Using the mean coordination number (MCN) of an OTS alloy as a comparative metric, we show that changes in data trends from several measurements are signatures of the transition from a floppy to a rigid glass network as described by TCT.

Intrinsic distribution of magnetic anisotropy in thin films probed by patterned nanostructures.

We demonstrate that the switching field distribution (SFD) in arrays of 50 nm to 5 microm Co/Pd elements, with perpendicular anisotropy, can be explained by a distribution of intrinsic anisotropy rather than any fabrication related effects. Further, simulations of coercivity and SFD versus element size allow the distribution of intrinsic anisotropy to be quantified in highly exchanged coupled thin films where the reversal mechanism is one of nucleation followed by rapid domain wall motion.

Domain wall creation in nanostructures driven by a spin-polarized current.

We report on current-driven magnetization reversal in nanopillars with elements having perpendicular magnetic anisotropy. Whereas only the two uniform magnetization states are available under the action of a magnetic field, we observed current-induced Bloch domain walls in pillars as small as 50 x 100 nm(2). This domain wall state can be further controlled by current to restore the uniform states.

Nanometer scale observation of high efficiency thermally assisted current-driven domain wall depinning.

Nanometer scale observation of the depinning of a narrow domain wall (DW) under a spin current is reported. We studied approximately 12 nm wide 1D Bloch DWs created in thin films exhibiting perpendicular magnetic anisotropy. Magnetotransport measurements reveal thermally assisted current-driven DW motion between pinning sites separated by as little as 20 nm.

Polymer mediated self-assembly of magnetic nanoparticles.

We present a simple polymer-mediated process of assembling magnetic FePt nanoparticles on a solid substrate. Alternatively absorbing the PEI molecule and FePt nanoparticles on a HO-terminated solid surface leads to a smooth FePt nanoparticle assembly with controlled assembly thickness and dimension. Magnetic measurements show that the thermally annealed FePt nanoparticle assembly as thin as three nanoparticle layers is ferromagnetic.

Deroughening of a 1D domain wall in an ultrathin magnetic film by a correlated defect.

Interaction of a field-driven magnetic domain wall with a correlated (line) defect is examined by Kerr imaging in subnanometer thin Co films. The line defect directs and confines the wall near the bottom of the effective potential trough U(eff), which competes with underlying random disorder that roughens the wall. We observe a kinetic "deroughening" with roughness exponent zeta approximately 0.