scientific staff

Prof. Dr. Rudolf Schäfer

technical staff

Stefan Pofahl

Dynamic microwave magnetometry


In order to investigate the dynamical magnetic processes of thin-film materials like exchange biased samples, we are using a technique called pulsed inductive microwave magnetometry (PIMM). The experimental setup, which is shown on the picture below, consists of a digital sampling oscilloscope, a pulse generator, a strip line, and two pairs of Helmholtz coils.

 

Simplified scheme of a PIMM setup.

The pulse generator produces magnetic field pulses with a rise time of about 80 ps.  A coplanar waveguide is used to deliver the field pulse to the sample. The transmitted pulse is detected by a sampling oscilloscope with a 12 GHz bandwidth. A trigger pulse for the sampling oscilloscope is derived from the pulse generator. Two Helmholtz coil pairs, calibrated with a Hall probe, are used to apply variable bias fields to the sample. To detect the inductive signal from the changing magnetization in the sample, and thus to extract the dynamic magnetization response, wave forms are measured with and without applied bias field and subsequently subtracted. 
Due to the very fast excitation in this experiment, time-dependent magnetic processes are minimized. Additionally, using large bias fields, coercivity effects can be eliminated. Dynamic magnetic properties like the ferromagnetic resonance frequency fres and the effective magnetic damping parameter α can be obtained (for example data see here).