Structural and magnetic study of heterogeneous CoxAg1-x films by resonance and magnetometric techniques

• Type: Article in International Scientific Journal
• Date: 1999

Authors

pogorelov, y. g. (Author) FCUP; G.N. Kakazei (Author) Other; sousa, j. b. (Author) FCUP; Kravets, AF (Author) Other; Lesnik, NA (Author) Other; de Azevedo, MMP (Author) Other; Malinowska, M (Author) Other; Panissod, P (Author) Other

Journal

Title: Physical Review B

Vol. 60

ISSN: 2469-9950

Publisher: American Physical Society

Indexing

ISI Web of Knowledge - 30 Citations

Scopus - 29 Citations

Other information

Authenticus ID: P-001-31D

DOI: 10.1103/physrevb.60.12200

Abstract (EN): The combined study of structural and magnetic properties of CoxAg1-x heterogeneous films in a wide concentration range 0.18<x<0.82 was performed using nuclear magnetic resonance (NMR), X-band ferromagnetic resonance (FMR), and superconductive quantum interferometer (SQUID) magnetometry. The structural investigation by NMR shows that at low Co concentrations rather large and pure cobalt clusters (similar to 3-nm diameter) coexist with much smaller ones of Co embedded in Ag rich, disordered (alloyed) regions. At x approximate to 0.4 large Co clusters coalesce (topological percolation). Above x = 0.5 there are Ag clusters in the Co matrix, which are larger and/or more irregular than the Co clusters for an equivalent, complementary composition. Both SQUID and FMR measurements indicate that the magnetic percolation, manifested by collective magnetic behavior of the granule ensemble, onsets already at x approximate to 0.3. Below this concentration the average size of the granules, obtained using both resonance techniques and SQUID, is 2.7-3.6 nm. At low Co concentration, the analysis of the SQUID magnetization data yields an atomic fraction of small clusters (similar to 0.5 nm) which is significantly larger than that observed in the NMR spectra, showing that most of the small clusters are still superparamagnetic at liquid-helium temperature. The observed FMR and magnetization behavior of CoxAg1-x films agrees well with the theoretical model developed in the framework of spherical isotropic interacting particles at low Co concentrations. At higher Co concentrations, a complex dynamics of uniform FMR precession is found, with two split modes due to the coupling between magnetic moments of individual granules and infinite ferromagnetic cluster, in agreement with a recent theoretical prediction. S0163-1829(99)05437-5].

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 7