Effect of Ar-N₂ Sputtering Gas on Structure and Tunneling Magnetodielectric Effect in Co-(Si-N) Nanogranular Films

We have investigated the effect of N-2 fraction x in Ar-N-2 sputtering gas on the tunneling magnetodielectric (TMD) effect in Co-(Si-N) nanogranular films. Co-(Si-N) films were deposited by co-sputtering Co and Si3N4 targets in Ar-x vol.%N-2 mixture gas with different N-2 gas fractions x of 0-30. All deposited films had a nanogranular structure composed of Co nanogranules with a diameter of 1-3 nm embedded in a Si-N matrix. We realized the TMD effect in the films for x >= 3.3, and the film deposited in Ar-6.6 vol.%N-2 gas showed the highest dielectric variations in a magnetic field. For 3.3 <= x <= 10, TMD peak frequency f(TMD) decreased from 17 to 40 kHz with increasing x because of the increase in intergranular spacing s. On the other hand, for 10 < x <= 30, f(TMD) increased from 40 kHz to 3.3 MHz as x increased since both s in the out-of-plane direction and beta, which indirectly represents the measure of the distribution of s, decreased. This study provides a new way to tailor the frequency response of the TMD effect.