Robustness of the remanent magnetic domain pattern formation and associated stripe-bubble transitions in Co/Pt multilayers against field sequencing

Abstract

Thin ferromagnetic [Co/Pt] multilayers with perpendicular magnetic anisotropy exhibit a variety of nanoscopic magnetic domain patterns at remanence, from long interlaced stripes to lattices of bubbles, depending on the multilayer structure but also on the magnetic history of the sample. For optimized structural parameters, stripe-bubble transitions accompanied by drastic increases in domain density have been observed when the magnitude of the previously applied perpendicular field Hm is finely tuned throughout the hysteresis loop. Here, we investigate the robustness of these morphological transitions against field sequencing and field cycling. We conducted this study on [Co(x)/Pt(7Å)]N=50 where x varies from 4 to 60 Å. We mapped the morphological transition with Hm varying from 0 to 9 T, following both an ascending sequence (0 → 9 T) and a descending sequence (9 T → 0). We found that the optimal field Hm = H* at which the domain density is maximized and its associated maximal density n* are not significantly affected by the field sequencing direction. We have also investigated possible pumping effects when cycling the applied field at the value H*. We found that n* remains relatively stable through field cycling, and much more stable in the bubble state, compared to longer stripe states. The observed robustness of these morphological transitions against field sequencing and field cycling is of crucial importance for potential magnetic recording applications.