Abstract
Magnetic liquids containing iron-oxide particles were investigated
by magnetization and Mossbauer measurements. The particles were
shown to be maghemite with a spontanious saturation magentization
Ms = 320 kA m-1 at 200 K and a normalized high-field
susceptibility x/M0 = 5.1x10-6 mkA-1, practically independent of
temperature. Ms increases with decreasing temperature according to
an effective Bloch law with an exponent larger than 1.5, as
expected for fine magnetic particles. The model of magnetic
particles with uniaxial anisotropy and the actual size
distribution gives a consistent description of independent
measurements of the temperature dependence of the hyperfine field
and the isothermal magnetization versus field. From this an
effective anisotropy constant of about 4.5x10 4 J m-3 is estimated
for a particle with diameter 7.5 nm. The magnetic relaxation, as
observed in zero-field-cooled magnetization and isothermal
remanence decay, is influenced by interactions and strongly
dependent on the applied magnetic field.
| Original language | English |
|---|---|
| Journal | Journal of Magnetism and Magnetic Materials |
| Volume | 173 |
| Pages (from-to) | 5-14 |
| ISSN | 0304-8853 |
| Publication status | Published - 1997 |