High Frequency Magnetic Property of Dense Fe₂₂Ni₇₈ Cluster Assembled Films

Abstract

Using a plasma-gas-condensation cluster deposition apparatus, Fe₂₂Ni₇₈ clusters are deposited on substrates. When a bias voltage, V_A, is applied to a substrate, neutral and charged clusters are formed in a plasma region and hard-landed on the substrate, forming dense Fe₂₂Ni₇₈ cluster assembled films. For specimens prepared without introduction of O₂ gas into a sputtering chamber (the oxygen flow rate, R_O2=0 mol/s), the magnetic coercivity, H_C, decreases, while the saturation magnetization, M_S, increases as V_A is increased up to 20 kV. The real part of magnetic permeability, μ′ is very small for V_A=0 kV and it becomes a few hundreds for V_A=5∼20 kV. For the dense Fe₂₂Ni₇₈ cluster-assembled films prepared at V_A=20 kV with R_O2≠0 mol/s, M_S decreases, while the magnetic anisotropy field, H_K, and the electrical resistivity, ρ, increase, and the ferromagnetic resonance frequency, f_FMR, increases up to a frequency (f) range of GHz. There are two magnetically optimized states: (1) μ′=760 at f=10 MHz for the specimen prepared at V_A=20 kV with the oxygen flow rate, R_O2=0 mol/s and the Ar flow rate, R_Ar=4.5×10⁻⁴ mol/s, and (2) μ′=370 at 10 MHz and f_FMR=1.10 GHz for the one prepared at V_A=20 kV with R_O2=3.7×10⁻⁸ mol/s and R_Ar=4.5×10⁻⁴ mol/s.