Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 33: Spindynamics / Switching III

MA 33.4: Talk

Friday, March 30, 2007, 11:45–12:00, H23

Microwave assisted switching of micron-sized magnetic elements — •Georg Woltersdorf, Christian Back, and Dieter Weiss — Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany

We use time resolved magneto optic Kerr effect microscopy to study the magnetic resonance and the switching of micron and sub-micron sized magnetic elements. The Permalloy microstructures have a uniaxial shape anisotropy and are prepared on a coplanar waveguide using e-beam lithography and dry etching. The thickness of the magnetic elements is kept below 2.5 nm to ensure that the single domain state is the ground state. In addition to the dynamic response the time resolved Kerr microscopy combined with synchronized microwaves allows one to measure static hysteresis loops on individual magnetic elements: in the experiment the synchronized microwaves are chopped and lock-in detection is used. The phase of the magnetic response to the microwaves changes by 180 degrees and hence the signal changes sign when the magnetization switches. Monitoring the signal as function of the applied magnetic field therefore allows one to measure the magnetic hysteresis for individual elements as small as 100 nm.

Hysteresis loops are measured as a function of microwave frequency and power. At large microwave powers these measurements show a strong reduction of the coercive fields. The effect is strongest at the resonance frequency of the magnetic element. At sufficiently large microwave powers the hysteresis loop collapses entirely.