Institut für Festkörperphysik



Soft/hard exchange spring media for perpendicular recording

A novel type of exchange spring media is proposed for magnetic recording systems consisting of a hard/soft ferromagnetic bilayer. Experimental measurements and finite element micromagnetic simulations show that the reversal modes induced by the external write field are significantly different from the thermally activated switching processes. Thus, the bilayers can be optimized in order to achieve a high thermal stability without increase of coercive field. In grains with identical size and coercivity an optimized bilayer reaches an energy barrier exceeding those of optimized single phase media by more than a factor of two. Additionally the lower angular dependence of coercivity of exchange spring media will improve the signal to noise ratio.

The exchange spring media based on FePt/Pt are proposed and can be optimized for both, high thermal stability and low coercivity. This differs significantly from the scope of pioneering work on exchange spring systems, aiming at an optimization of energy product of bulk permanent magnets and thin films.

D. Suess, T. Schrefl, S. Fähler, M. Kirschner, G. Hrkac, F. Dorfbauer, and J. Fidler,
APPLIED PHYSICS LETTERS 87, 012504, (2005).

Exchange FM/FM Spring Media

Fig.1: Numerical micromagnetic simulation of the transient state of the magnetization reversal in a soft/hard bilayer based on FePt alloys.
Contact: J. Fidler, D. Suess