Magnetic states of granular layered CoFe-Al2O3 system

• Type: Article in International Scientific Journal
• Date: 2001

Authors

sousa, j. b. (Author) FCUP; G.N. Kakazei (Author) Other; pogorelov, y. g. (Author) FCUP; Santos, JAM (Author) Other; Petracic, O (Author) Other; Kleemann, WW (Author) Other; Binek, C (Author) Other; Cardoso, S (Author) Other; Freitas, PP (Author) Other; de Azevedo, MMP (Author) Other; Lesnik, NA (Author) Other; Rokhlin, M (Author) Other; Wigen, PE (Author) Other

Journal

Title: IEEE Transactions on Magnetics

Vol. 37

Pages: 2200-2203

ISSN: 0018-9464

Publisher: IEEE

Indexing

ISI Web of Knowledge - 7 Citations

Scopus - 7 Citations

Other information

Authenticus ID: P-000-V2E

DOI: 10.1109/20.951123

Abstract (EN): The granular layered magnetic system Co80Fe20 (t)/Al2O3 (3 nm), where the Co80Fe20 layers of nominal thickness t form separate, almost spherical magnetic granules of typical diameter 2-3 mn between the Al2O3 spacers, was studied. We discuss measurements of the dc and ac magnetic susceptibility chi for 1 nm < t < 1.3 nm at temperatures 10 K < T < 300 K and ac frequencies 0.01 Hz < f < 10(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 Mel-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 Hue on this diagram is confirmed.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 4