Abstract
The structural evolution and magnetic properties of nanostructured
copper ferrite, CuFe2O4, have been investigated by X-ray
diffraction, Mossbauer spectroscopy, and magnetization
measurements. Nanometre-sized CuFe2O4 particles with a partially
inverted spinel structure were synthesized by high-energy ball
milling in an open container with grain sizes ranging from 9 to 61
nm. Superparamagnetic relaxation effects have been observed in
milled samples at room temperature by Mossbauer and magnetization
measurements. At 15 K, the average hyperfine field of CuFe2O4
decreases with decreasing average grain size while the coercive
force, shift of the hysteresis loop, magnetic hardness, and
saturation magnetization at 4.2 K increase with decreasing average
grain size. At 295 K the coercive-field dependence on the average
grain size is described, with particles showing superparamagnetic
relaxation effects. At 4.2 K the relationship between the coercive
field and average grain size can be attributed to the change of
the effective anisotropy constant of the particles. The interface
anisotropy of nanostructured CuFe2O4 is found to be about
1.8(1)*10(5)erg cm-3. Although spin canting was present,
approximately 20% enhancement of the saturation magnetization in
CuFe2O4 nanoparticles was observed, which could be explained by a
cation redistribution induced by milling. The high-field
magnetization irreversibility and shift of the hysteresis loop
detected in our samples have been assigned to a spin-disordered
phase, which has a spin-freezing temperature of approximately 50 K.
Original language | English |
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Journal | Journal of Physics Condensed Matter |
Volume | 11 |
Issue number | 20 |
Pages (from-to) | 4063-4073 |
ISSN | 0953-8984 |
Publication status | Published - 1999 |