Scanning Thermal Microscopy and Ballistic Phonon Transport in Lateral Spin Valves.

Using scanning thermal microscopy, we have mapped the spatial distribution of temperatures in an operating nanoscale device formed from a magnetic injector, an Ag connecting wire, and a magnetic detector. An analytical model explained the thermal diffusion over the measured temperature range (2-300 K) and injector-detector separation (400-3000 nm). The characteristic diffusion lengths of the Peltier and Joule heat differ remarkably below 60 K, a fact that can be explained by the onset of ballistic phonon heat transfer in the substrate.

Beyond the compact magnetic domain wall.

Domain wall dynamics in wide submicrometer wires is investigated to understand the fundamental mechanisms that limit wall mobility, both experimentally by magneto-optical Kerr effect and by micromagnetic simulations. It is found that the dynamic domain wall structure departs significantly from the current description of a compact entity when evolving along the wire. The wall is composed of several substructures, each one propagating and evolving in a different dynamic regime with very different velocities.

Magnetologic devices fabricated by nanostencil lithography.

We present magnetic quantum cellular automata (MQCA), fabricated by means of nanostencil lithography, i.e., using a resistless shadow masking technique in ultra-high vacuum. The nanostencil tool allows the fabrication and in situ investigation of structures using atomic force microscopy (AFM) and magnetic force microscopy (MFM). We analyze the error distribution within the structures to shed light on the performance and challenges of magnetic cellular logic devices. Simulations are performed to corroborate an improved concept for these devices which makes use of fourfold magnetic anisotropy.

Dependence of domain-wall depinning threshold current on pinning profile.

We have investigated the threshold current density required for depinning a domain wall from constrictions in NiFe nanowires, which give rise to pinning potentials of fixed amplitude but variable profile. We observed it to vary linearly with the angle of the triangular constriction. These results are reproduced using micromagnetic simulations including the adiabatic and nonadiabatic spin-torque terms. By curve-fitting the calculated variations to the experimental results, we obtain the nonadiabaticity parameter beta=0.04(+/-0.005) and current spin polarization P=0.51(+/-0.02).