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 magneto-dielectric (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 to 30. All deposited films had a nanogranular structure composed of Co nanogranules with a diameter of 1 to 3 nm embedded in an 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 MHz to 40 kHz with increasing x because of the increase in intergranular spacing s . On the other hand, for 10 < x ≤ 30, fTMD increased from 40 kHz to 3.3 MHz as x increased since both s in the out-of-plane direction and β, 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.