Curie temperature of multiphase nanostructures

R. Skomski, D. J. Sellmyer

Research output: Contribution to journalConference article

36 Scopus citations

Abstract

The Curie temperature and the local spontaneous magnetization of ferromagnetic nanocomposites are investigated. The macroscopic character of the critical fluctuations responsible for the onset of ferromagnetic order means that there is only one Curie temperature, independent of the number of magnetic phases present. The Curie temperature increases with the grain size and is, in general, larger than predicted from the volume averages of the exchange constants. However, the Curie-temperature enhancement is accompanied by a relative reduction of the spontaneous magnetization. Due to the quadratic dependence of the permanent-magnet energy product on the spontaneous magnetization, this amounts to a deterioration of the magnets performance. The length scale on which an effective intergranular exchange coupling is realized (coupling length) depends on the Curie-temperature difference between the phases and on the spacial distribution of the local interatomic exchange. As a rule, it is of the order of a few interatomic distances; for much bigger grain sizes the structures mimic an interaction-free ensemble of different ferromagnetic materials. This must be compared to the magnetic-anisotropy coupling length, which is of the order of 10 nm. The difference is explained by the nonrelativistic character of the Curie-temperature problem.

Original languageEnglish (US)
Pages (from-to)4756-4758
Number of pages3
JournalJournal of Applied Physics
Volume87
Issue number9 II
DOIs
StatePublished - May 2000
Event44th Annual Conference on Magnetism and Magnetic Materials - San Jose, CA, United States
Duration: Nov 15 1999Nov 18 1999

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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