Separation of rf-collapse effect from heat-narrowing in permalloy foil samples

Abstract

In rf-collapse of hyperfine field of soft ferromagnetic metal samples, ambiguity arises due to eddy current heating that rf field induces, which progressively narrows the Hfs-spectrum with increasing rf power, ultimately reducing it to a single unsplit line above Curie point. We report experiments with perforated permalloy foils. In these, path for local eddy current loops are broken reducing the eddy current heating, as against only removal of heat generated, in many previous collapse studies. The effect of rf-collapse can be demonstrated conclusively when it is seen in conjuction with presence of internal magnetic field. For this purpose, we took spectra in switched rf field experiments, where rf switch-OFF and ON cycle was synchronised to the two halves of velocity sweep. Results clearly shows Hfs-spectrum when rf field is OFF and rf-collapse when rf field is ON.