Magnetic and field emission studies of atom beam sputtered Ni:SiO2 granular films

Ni:SiO₂ granular films have been prepared by atom beam sputtering technique under ambient conditions. These films have been subsequently annealed at 200-600 °C temperature. GAXRD and TEM analyses show the growth of Ni particles and improvement in crystallinity with increase in annealing temperature. Selected area electron diffraction and XPS analyses show the presence of a small quantity of NiO phase in addition to metallic Ni. Room temperature magnetic measurements indicate that the films annealed at lower temperatures (≤400 °C) are superparamagnetic and the film annealed at 600 °C is ferromagnetic. Magnetic results at 5 K are explained on the basis of exchange bias between Ni particles and surrounding nickel oxide. Systematic field emission studies on as-deposited and annealed films show a turn-on field ∼6.2-13.5 V/μm corresponding to an emission current density of ∼1 A/m². Field emission results are explained on the basis of electrical inhomogeneity effects.