Growth, structural, and magnetic properties of high coercivity Co/Pt multilayers

Abstract

Co/Pt multilayer films ([Co (t Co nm)/Pt(1 nm)] 10 , 0.2<t Co <2 nm) with perpendicular magnetic anisotropy and room temperature coercivity H c = 12-15 kOe are fabricated using electron beam evaporation at elevated growth temperatures onto Si(001)/SiN x (40nm)/Pt(20nm) substrate/seed structures. Hysteresis and magnetic force microscopy (MFM) studies indicate changes in the magnetization reversal mechanism along with a sharp increase in coercivity for growth temperatures higher T G ∼ 230 -250 o C. Films grown at T G < 230 o C (t Co = 0.2 -0.4 nm) show large micrometer size magnetic domains and rectangular hysteresis loops indicating magnetization reversal dominated by rapid domain wall motion throughout the film following nucleation at H n ~ H c . Films grown at T G > 250 o C show fine-grained MFM features on the sub-100 nm length scale and hysteresis studies indicate reversal dominated by localized switching of small clusters. The hysteresis curves for the highest coercivity films are sheared with with a hysteresis slope α=4πdM/dH|Hc≅1.5, which is close to the ideal value for completely decoupled grains of α =1. High resolution cross-sectional TEM with elemental analysis shows columnar grains extending throughout the multilayer stack. Sharp Co/Pt interfaces are found from TEM and grazing incidence X-ray diffraction. At higher T G , Co depletion and structural defects at the grain boundaries provide a mechanism for exchange decoupling of adjacent grains, which may result in the high coercivities observed. Anisotropy and magnetization values are estimated as K u ~ 8x10 6 erg/cc and M S ~ 450 emu/cc (per total volume), hence H k = 2K u /M S ~ 17.5 kOe for the highest coercivity H c ~ 15 kOe films.

Influence of interface exchange coupling in perpendicular anisotropy[Pt/Co]50/TbFebilayers

“…However, the TbFe magnetization reversal is very different for the two samples. ͒ are similar to previous observations in perpendicularly magnetized samples 16 and is indicative of the formation of lateral domains created to minimize the dipolar interactions. For sample A the magnetization loops obtained at the Fe and Co edges are qualitatively different.…”

“…The ͓Pt͑0.75 nm͒ / Co͑0.25 nm͔͒ 50 multilayer exhibits a strong out-of-plane anisotropy, as observed in similar systems. 16 Tb 30 Fe 70 is a ferrimagnetic alloy where the Tb moments are oriented antiparallel to the Fe moments. The system shows a strong perpendicular anisotropy.…”

Magnetic Films on Nanoparticle Arrays

“…In addition, superconductive quantum interference device hysteresis measurements have been performed on these film samples to extract the effective magnetic anisotropy, revealing a transition of easy axis orientation from perpendicular to the film plane to an in-plane direction at a Co layer thickness of about 0.8 nm. These results are consistent with experimental data reported in the literature [46,53]. After SRT at t Co = 0.8 nm, remanence magnetization measured in the out-of-plane direction decreases (Fig.…”

Asymmetric Domain Nucleation and Unusual Magnetization Reversal in Ultrathin Co Films with Perpendicular Anisotropy

“…The magnetization reversal in Co=Pt n multilayers consisting of many repeats differs drastically [9][10][11][12][13][14][15][16][17] from that of ultrathin Co films. The reversal in multilayers with a large n (e.g., n 50 [14]) also begins by the nucleation of small bubble domains.…”