Abstract
The granular layered magnetic system Co/sub 80/Fe/sub 20/(t)/Al/sub 2/O/sub 3/ (3 nm), where the Co/sub 80/Fe/sub 20/ layers of nominal thickness t form separate, almost spherical magnetic granules of typical diameter 2-3 nm between the Al/sub 2/O/sub 3/ spacers, was studied. We discuss measurements of the dc and ac magnetic susceptibility /spl chi/ for 1 nm <t<1.3 nm at temperatures 10 K<T<300 K and ac frequencies 0.01 Hz<f<10/sup 3/ Hz, revealing a rich variety of magnetic states, including superparamagnetic (SPM), ferromagnetic (FM)-like, and glass (G)-like. In order to describe the ac response in this disordered planar system, a generalization of the Neel-Brown approach is proposed, including random anisotropy and random molecular fields acting on the granules. The observed magnetic states are summarized in a phase diagram in the variables t-T, which is explained through the competition of thermal energy with two kinds of interaction between granules: usual dipolar (point-like) and FM exchange (due to stray dipolar fields from nonspherical granules). In particular the coincidence of maximum low field sensitivity dMR/dH with the SPM-FM transition line on this diagram is confirmed.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
