Domain walls in AF/FM magnetic bilayers. (News Briefs).

The exchange coupling between a ferromagnet (FM) and an antiferromagnet (AF) creates a magnetic bias field on the ferromagnet and thereby controls its magnetization characteristics. Discovered more than 40 years ago, this perplexing phenomenon has been intensely studied in recent years, and has been incorporated in the new high sensitivity computer disk read heads that have enabled multiple-gigabyte hard disks.

Using the NIST-developed magneto-optical indicator film technique, NIST researchers have observed directly for the first time the antiferromagnet domain walls and the evolution of a special type of hybrid domain wall in exchange-coupled FM/AF bilayers. We accomplished this using special samples demagnetized at high temperature and cooled to room temperature in zero field. In such samples, we discovered the presence of a hybrid domain wall consisting of coincident ferromagnet and antiferromagnet sections. Under an applied magnetic field, the ferromagnet domain wall moves while the antiferromagnet wall remains stationary. In the process, an exchange spring develops that connects the moving ferromagnetic and the stationary antiferromagnetic domain walls.

As a consequence of the winding and unwinding of the exchange spring during the backward and forward magnetization reversals, a shifted hysteresis loop is observed. These results should enable magnetic recording disc manufacturers to prepare more reliable and controlled devices since now they know what magnetic features to control and how to examine them.

CONTACTS: Alexander Shapiro, [phone]; [e-mail] or Robert Shull, [phone]; [e-mail].