Influence of structural disorder on magnetic domain formation in perpendicular anisotropy thin films

Abstract

Using a combination of resonant soft x-ray scattering, magnetometry, x-ray reflectivity and microscopy techniques we have investigated the magnetic properties and microstructure of a series of perpendicular anisotropy Co/Pt multilayer films with respect to structural disorder tuned by varying the sputtering deposition pressure. The observed magnetic changes in domain size, shape and correlation length originate from structural and chemical variations in the samples, such as chemical segregation and grain formation as well as roughness at the surface and interfaces, which are all impacted by the deposition pressure. All samples exhibited short range "liquid-like" positional ordering over significant portions of their major hysteresis loops, while only the lowest disorder samples showed evidence of a random "gas-like" distribution of magnetic domains, present just after nucleation and as well as prior to saturation. The structural and chemical disorder induced by the higher deposition pressure first leads to an increase in the number of magnetic point defects that limit free domain wall propagation. Then, as the sputtering pressure is further increased, the domain wall energy density is lowered due to the formation of local regions with reduced magnetic moment, and finally magnetically void regions appear that confine the magnetic domains and clusters, similar to segregated granular magnetic recording media.

Helicity and field dependent magnetization dynamics of ferromagnetic Co/Pt multilayers

“…Changes of the deposition pressure allows tuning the film microstructure from a continuous film to magnetically isolated grains. 28 All the samples demonstrated perpendicular magnetic anisotropy and 100% remanence. The magneto-optical static characterization revealed an increase of the coercive field from with increasing argon pressure from 3 mTorr to 8.5 mTorr.…”

Effect of substrate temperature on the magnetic properties of epitaxial sputter-grown Co/Pt

“…Their attractive properties include perpendicular magnetic anisotropy (PMA) and a large polar magneto-optic Kerr effect (MOKE) at short wavelengths 4 . More recently Co/Pt has become an interesting system for the study of the physics of domain walls (DWs) [5][6][7][8] , and spin torque [9][10][11][12][13] . The PMA leads to the formation of narrow, nanometre-scale DWs, and the large polar Kerr effect is convenient for measuring the DW motion.…”

Influence of magnetic domain size on dipolar interactions and hysteresis field asymmetry in layered high/low coercivity perpendicular anisotropy systems

“…Indeed, if there were no domains inside the LCL, the most energetically stable position for the new LCL domain, would be on top of the HCL domains. 6 From X ¼ 8 to X ¼ 15, the density of LCL domains increases since the mean domain size decreases (as explained above).…”

“…This difference is due to the increase of the multilayer interface, roughness, and crystallographic defects induced by the higher deposition pressure. 6 These defects usually lead as well to a higher coercivity and the magnetization reversal process of the high pressure film is then dominated by more frequent domain nucleation processes. Fig.…”

“…10 multilayer at 7 mTorr Argon pressure. 6 Various single and high/low coercivity bilayer samples have been grown with 5 X 30. The macroscopic magnetic properties were measured using a commercial Vibrating Sample Magnetometry (VSM).…”