Improved grain isolation of Co/sub 80/Pt/sub 20/ films via grain boundary diffusion of Mn

Abstract

Post-deposition rapid thermal annealing (RTA) was performed on the Cr-less Co20at%Pt alloy with a Mn diffusion layer on top. A value of about 8 10 6 erg/cm 3 was obtained for the as-deposited film and it decreased only up to about 10% after annealing. The high intergranular exchange coupling of the as-deposited CoPt film was suppressed by RTA and the coercivity increased dramatically from about 2200 to 6000 Oe. The energyfiltered TEM plane-view images showed depletion of Co and aggregation of Mn at the CoPt grain boundaries. This is a direct evidence supporting preferential diffusion of materials from adjacent layers into magnetic grain boundaries.

Rapid thermal processing of magnetic materials

“…It is seen that the films with a CrMn intermediate layer have a microstructure characterized by a smaller and a more evenly distributed grain size. Subsequent works performed by Zou et al [116] revealed a significant increase in coercivity by 38% for CoCrPt/CrTi/NiAl film and even by 60-73% in Mn-capped CoCrPt/CrTi/NiAl film. The reason for the increase of coercivity was attributed to better grain isolation since the RTP promotes the diffusion of adjacent Mn layers into the grain boundary, resulting in the breakup of the exchange-coupling.…”

“…The segregation may also lead to an increase in coercivity as a consequence of the reduction in exchange-coupling between neighbouring magnetic grains. Because of the reduction in intergranular exchange-coupling, the collective magnetic reversal via domain wall motion across grain boundaries can also be suppressed [116]. Controlling grain boundary diffusion by RTP is an ideal way of improving the segregation because, upon subjecting the film to a high temperature for a long time in conventional annealing, the segregation will be destroyed [117].…”