Magnetic properties of nanosize nickel particles produced in silica glasses by ion-implantation and subsequent annealing

When Ni⁺ ions are implanted into silica glasses at a dose of 6 × 10¹⁶ cm^-2 at 160 keV and 3 μA cm^-2, nanosize Ni particles (6.5 ± 1.5nm) of spherical shape are produced in the implanted layer, as confirmed by transmission electron microscopy (TEM), electron diffractometry and X-ray photoelectron spectroscopy. The relative intensity of ferromagnetic resonance (FMR) absorption at 298 K increases by a factor of ∼ 12 after annealing in 4%H₂ + 96%Ar for 4 h, although the Ni particle size observed by TEM does not change during this treatment. The mean Ni particle size, obtained from the temperature dependence of FMR intensity, increases from ∼4.5 nm to ∼5.5 nm by annealing. Magnetocrystalline anisotropy is observed in the FMR spectrum, measured at 133 K, of the annealed sample. The increase in FMR intensity by annealing is, therefore, attributed to an increase in the crystallinity of the Ni particles.