Abstract
We present a study on magnetic properties of CuFe2O4
nanoparticles, produced by high-energy ball milling. The series of
samples obtained, with average particle sizes LFAN alpha d RTAN
ranging from 61 nm to 9 nm, display increasing relaxation effects
at room temperature. Irreversibility of the magnetization and
shifts to negative fields in the hysteresis loops are observed
below T-f APEQ 55 K, indicating unidirectional magnetic anisotropy
in milled samples. These features could be explained by assuming
the formation of a spin-disordered surface layer, which is
exchange-coupled to the ferrimagnetic core. The temperature
dependence of average hyperfine field, saturation magnetization
and coercive field shows a change of slope at T-f, indicating the
spin freezing of the disordered phase at T-f. From the H-C(T)
curves below T-f, the thickness of the surface layer was found to
increase as the average grain size decreased, reaching t EQ 2.6(6)
nm for the sample having LFAN alpha d RTAN EQ 9(3) nm. The
anisotropy constant value for the disordered phase was estimated
to be K-I/EQ 9(1) MUL alpha 10-5 erg cm+3.
Original language | English |
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Journal | Materials Science Forum |
Volume | 312 |
Pages (from-to) | 545-550 |
ISSN | 0255-5476 |
Publication status | Published - 1999 |