The optical and magnetic properties of Ni⁺-implanted silica

Fused silica plates were implanted with ⁵⁸Ni⁺ at room temperature to a dose of 6 × 10¹⁶ ions cm^-2 under the condition of 160 keV and 3 μA cm^-2. The changes in the optical and magnetic properties of Ni⁺-implanted silica by annealing at 800°C for 4 h in air, N₂ and Ar with 4% H₂ were measured to determine the chemical state of implanted nickel species. The absence of change in the depth distribution of Ni after annealing under these conditions indicates that nickel species did not dissolve in silica. The absorption band due to the surface plasmon resonance of Ni particles at ∼ 3.6 eV decreased and increased on annealing in air and Ar with 4% H₂, respectively. The intensity of the ferromagnetic resonance signal measured at -196°C was larger than that at room temperature, both increasing with heat treatment. The resonance field depended on the angle between the implanted surface and the applied magnetic field. It is concluded that Ni particles embedded in silica by ion-implantation were magnetized in the plane normal to the ion beam and that super-paramagnetic Ni changed to ferromagnetic Ni during the thermal treatment.