Hi Nick, That'd be called barkhausen noise; a magnetic effect even your dog can pronounce. The "wooshing" is caused by the unpinning of domain walls, if you look carefully at the signal with a scope you can see the individual avalanches of domain motion.
Try it with various samples of transformer iron, I'm sure you can find certain samples that will show the effect very strongly. Your "bahhh" instinct is correct, the effect was discovered in 1919. Google on that keyword for more information, and consult your Bozorth for details. You do have a copy of Bozorth, huh? Well buy a used one, for bogs sake! Indispensible ref for things magnetic. K. -----Original Message----- From: Nick Reiter [mailto:[EMAIL PROTECTED] Sent: Friday, November 25, 2005 4:28 PM To: [email protected] Subject: Radio Free GMR ...or what is the sound of one electron flipping? Rather than go into a long winded preface describing the circumstances of a curious little effect I have been listening to lately, let me toss this out to the scholars of electrons. Is anyone aware of a source of white noise in electronic circuits that is related to either magnetic domain or electron spin polarization? (Or de-polarization?) I've been playing with non- or micro-inductive coils made from ferromagnetic materials (nickel wire mainly) and I've found a neat effect that manifests as a burst of strong hissy white noise "whooshing" when a large magnet is moved by hand toward the coil. To get a second whoosh , I have to pull the magnet away, flip it over to the opposite polarity, and then push it toward the coil again. As if the burst of white noise comes from domains being de-polarized and re-polarized... hysteresis noise? Replicating the actions with an identical coil made from copper wire produces no such effect at all. Just starting to play wit' dis' one, so my reports may be sporadic here. My "bahhhh" nature says that this must be something well known, but I've never run into it before. Still, I've been thinking along the lines of spin-spin communication, and more pragmatically, spin polarized radio. I've been trying to bone up on GMR and spin valve materials technology. Maybe there is some connection here? NR __________________________________ Yahoo! Music Unlimited Access over 1 million songs. Try it free. http://music.yahoo.com/unlimited/
