A team of physicists has answered a long-standing question about the exchange bias between anti-ferromagnets (AFM) and ferromagnets (FM) used in computers hard disks that could spawn better, faster, and higher-density drives.
For the first time, researchers from Arizona State University, IBM Almaden Research Labs and Lawrence Berkeley Laboratory's Advance Light Source collaborated to show that the alignment between electron spins are colinear across an AFM and FM interface. The findings are published in the June 16, 2000 edition of Nature.
Exchange bias occurs when the exchange coupling of ferromagnetic and anti-ferromagnetic films across their common interface causes a shift in the hysteresis loop of the ferromagnet. The effect was first discovered in 1956, although its origin was never confirmed. Since then, physicists have tried to understand how the arrangement of spins at interfaces in a layered magnetic material affects the properties of that material.
Exchange bias is useful in controlling the magnetization in heads used in magnetic disk storage. Today nearly all hard drives use anti-ferromagnets in the reader head.
Michael R. Scheinfein, a physics professor at Arizona State University and one of the paper's authors, said by using a polarized x-ray magnetic dichroism spectromicroscopy that separately revealed the micromagnetic structure on both sides of the interface, it was possible to confirm an AFM and FM colinear alignment.
"Remanent hysteresis loops recorded for individual ferromagnetic domains show a local exchange bias, and we now have evidence that the alignment of FM spins is determined, domain by domain, by the spin directions in the underlying AFM," said Scheinfein.
The results also demonstrate the usefulness of spectromicroscopy for determining the micromagnetic structure on each side of interfaces in thin films.
Sources: Michael R. Scheinfein, (480) 965-9658 or (503) 726-2783
Nature