Effect of pH on Structural, Magnetic and FMR Properties of Hydrothermally Prepared Nano Ni Ferrite |
Sadeq H.Lafta |
Abstract |
Nano nickel ferrite particles were prepared at pH
values 1.5, 4, 7, 10, 13 by a hydrothermal method using metal
chlorides and NaOH as an oxidant and solution basicity
controller. There is a phase transition from hematite to
spinel ferrite that begins when the pH reaches 4. The lowest
crystallite size (4 nm) was associated with a highest lattice
constant (8.345 Å), at pH=4. Whereas maximum crystallite
size 64.5 nm corresponds lattice constant of 8.298 Å at
pH=10. The highest magnetization (48 emu/g) value was
achieved for the sample prepared at pH=7, which at the
same time has a lower coercivity. The samples synthesized
at pH ≥4 show superparamagnetic behavior owing to its
low particle size and to zero field cooling and field cooling
measurements. The ferromagnetic resonance (FMR) cavity
tests analysis show that the broadened linewidth (770
Oe) and high imaginary permeability or high microwave
absorption which is linked to high magnetization and
low coercivity of superparamagnetic particles and their
aggregation. There was a shift in the resonance field due
to internal fields and cation distribution. |