Sensitive Pulsed Magnetoresistive Measurement of Magnetic Film Hk

Publisher Website
Google Scholar
Abstract
For a magnetic annealing experiment with Permalloy films it was necessary to measure the uniaxial anisotropy field Hk without breaking vacuum after deposition, while maintaining a transverse field H⊥≳Hk. The annealing mechanism could then be studied as a function of temperature by a plot of Hk vs time. In the presence of the field H⊥, longitudinal ac (500 cps) field H∥«Hk, and longitudinal dc film current, a second harmonic magnetoresistance signal is generated. The measurement is based on the phase reversal of this signal when H⊥ = Hk. Rather than sample only one cycle of the 2nd harmonic output, 30 cycles are used and averaged in an integrator. The transverse field consists of a dc bias and a 1‐cps triangular or sinusoidal waveform. The minimum resultant field is maintained at Hk by means of negative feedback to the dc bias. Typical system performance is as follows: For an Hk of 5 Oe, ΔHk is readable to 0.01 Oe or 0.2%. Absolute value of Hk is measured to about 5% accuracy. The system will follow changes at a maximum rate of 0.2 Oe/sec. A second‐generation system will also be described which uses simpler electronics and is more flexible with regard to the annealing and sensing directions of the film.

This publication has 1 reference indexed in Scilit: