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

We have investigated the effect of N2 fraction
$x$
in Ar–N2 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.%N2 mixture gas with different N2 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
$x \ge3.3$
, and the film deposited in Ar-6.6 vol.%N2 gas showed the highest dielectric variations in a magnetic field. For
$3.3\le x \le10$
, TMD peak frequency
$f_{\mathrm {TMD}}$
decreased from 17 to 40 kHz with increasing
$x$
because of the increase in intergranular spacing
$s$
. On the other hand, for
$10 < x \le30$
,
$f_{\mathrm {TMD}}$
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.