The high field, high frequency permeability of narrow, thin-film magnetic stripes

The authors report measurements of the magnetic response of arrays of narrow Permalloy stripes using a high field permeameter. The permeameter operates in a swept frequency mode from 300 KHz to 30 MHz with a field amplitude of up to 5 Oe. Using this device, two modes of flux conduction, rotation and wall motion, can be observed in narrow Permalloy stripes. The low field-amplitude permeability of narrow unlaminated Permalloy stripes is frequency independent except for eddy current losses as expected for magnetization rotation. At higher fields the magnetic response increases at frequencies below 10 MHz with increasing drive amplitude as domain wall motion becomes significant. Results are consistent with the expected domain wall mobility (around 2×10³ cm/(s-Oe) for 2-μm-thick films). Because of the high density of wall in microscopic structures, wall motion is the dominant flux conduction mechanism below 30 MHz at high drive fields