The temperature dependence of domain-wall depinning in permalloy nanowires is investigated by measuring depinning fields and corresponding depinning times as a function of the external magnetic bias field. Domain walls are pinned at triangular notches in the nanowires and detected noninvasively by Hall micromagnetometry. This technique allows one to acquire depinning-field and depinning-time distributions in the temperature range between 5 and 50 K and thus to determine the stochastics of the depinning process. The results are discussed in terms of the Néel-Brown model for thermally activated magnetization reversal, assuming a single energy barrier to overcome. In general, the cases presented deviate from this description and give a clear indication that a more complex term for the energy landscape of domain-wall depinning at constrictions in nanowires is obligatory.

We use ballistic Hall micromagnetometry to determine depinning fields of domain walls (DWs) in Permalloy nanowires in the temperature range between 5 and 50K. The walls are pinned in constrictions defined by a triangularly shaped notch on one side of the wire. The high sensitivity of the Hall sensor to local stray fields allows the detection of individual DWs and a distinction of different wall types. A strong temperature dependence of the depinning fields is observed that can be described by a model with a single energy barrier. For temperatures above 20K, additional types of DWs occur.

We present experiments and micromagnetic simulations on Hall micromagnetometry of magnetic vortices. The magnetization reversal in a 2×2 μm2 Permalloy square of 20 nm thickness is investigated at liquid helium temperatures. Nucleation, displacement, and annihilation of the vortex state in an external magnetic field are observed by detecting its stray field. The findings are corroborated by images taken with a magnetic-force microscope at room temperature. The experimental data are compared to micromagnetic simulations.

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