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.

Finite image size effects on the characterization of magnetic domain patterns via magnetic force microscopy

“…To address the finite size effect question, we study here three MFM images with distinctive domain patterns: stripe, bubble and mixed patterns. These patterns were observed in [Co (3 nm) /Pt (0.7 nm)] N multilayers exhibiting PMA, where the Co thickness of 3 nm and the number of repeat N had been optimized to maximize domain densities, based on our previous studies [13,14]. The bubble and stripe patterns were achieved in the same material, for which N = 20, by applying an out-of-plane magnetic field of different magnitudes: 4 kOe for the stripe pattern and 6 kOe for the bubble pattern.…”

“…To best characterize and control these morphological transitions, one needs to well visualize the magnetic domain patterns in the film at the nanoscale. [12,14] With spatial resolution down to ≈ 20-25 nm, magnetic force microscopy (MFM) is a common way to image nanoscale magnetic domain patterns in thin ferromagnetic films with PMA. However, the scanning nature of MFM often requires limiting the size of the image, typically in the range of 1 -20 m and finding a tradeoff between the scanning duration and spatial resolution.…”