Magnetic properties of ultrafine Co particles

Author

Gangopadhyay, S. ; Hadjipanayis, G.C. ; Sorensen, C.M. ; Klabunde, K.J.

Author_Institution

Dept. of Phys. & Astron., Delaware Univ., Newark, DE, USA

Volume

28

Issue

5

fYear

1992

fDate

9/1/1992 12:00:00 AM

Firstpage

3174

Lastpage

3176

Abstract

Fine particles of Co in the size range of 50-350 Å by the vapor deposition technique have been prepared. The dependence of magnetization on size and temperature has been studied. A maximum coercivity of 1500 Oe was obtained for a particle size of 350 Å. Magnetic and structural measurements indicate a shell-type structure with an FCC (face centered cubic) Co core surrounded by a Co-oxide shell. The effect of exchange interactions between the antiferromagnetic Co-oxide shell and the ferromagnetic Co core on the magnetic behavior of the powders has been investigated. The core/shell structure is responsible for the large coercivities present at cryogenic temperatures and the nonsaturation effects, which increase with decreasing particle size and with higher oxidation. The disappearance of the shift at 150 K marks the loss of exchange interaction between the Co-core and its CoO oxide coating. Thus the 150 K temperature could either be the blocking temperature or the Neel temperature of CoO crystallites present in the oxide shell

Keywords

cobalt; coercive force; exchange interactions (electron); ferromagnetic properties of substances; magnetic properties of fine particles; magnetisation; particle size; 50 to 350 Å; CoO crystallites; FCC core; Neel temperature; antiferromagnetic oxide shell; blocking temperature; coercivity; cryogenic temperatures; exchange interactions; ferromagnetic core; magnetic behavior; magnetization; nonsaturation effects; particle size; shell-type structure; structural measurements; ultrafine Co particles; vapor deposition; Antiferromagnetic materials; Chemical vapor deposition; Coercive force; Elementary particle exchange interactions; FCC; Magnetic cores; Magnetic properties; Magnetization; Powders; Temperature dependence;

fLanguage

English

Journal_Title

Magnetics, IEEE Transactions on

Publisher

ieee

ISSN

0018-9464

Type

jour

DOI

10.1109/20.179749

Filename

179749