What does AF stand for?

257 QC793 Physicists and materials scientists report recent research in the three areas from such perspectives as a homotopy theory of topological defects in ferromagnetic, anti-ferromagnetic, and cyclic spinor condensates; high spin field theories and relativistic; recent advances in developing borate crystal growth; and crystal growth from pharmaceutical melts.

This is reportedly achieved by using an anti-ferromagnetic media instead of an aluminium one.

While there, he oversaw the company's transition as the first independent media supplier to provide synthetic anti-ferromagnetic disks.