Magnetic Properties of Nanocrystalline and Amorphous FeCoC Thin Films

FeCoC thin films are prepared by reactive sputtering. Acetylene (C
₂
H
₂
) gas is introduced to control the C composition in the films by adjusting the acetylene partial pressure (P
_acetylene
/P
_Ar
). According to X-ray diffractometry and transmission electron microscopy results, the microstructure of the films changes from well crystalline to nanocrystalline and even to amorphous with the increase of acetylene partial pressure. Results show that the value of the saturation flux density (4piM
_s
) decreases slowly from 24.5 to 23.5 kG with the increase of acetylene partial pressure (P
₂
H
₂
/PAr) from 0% to 1%. The 4pi M
_s
decreases dramatically with acetylene partial pressure higher than 1%. Coercivity in both the hard axis and easy axis directions shows minimums around the acetylene partial pressure of 1%. H
_ch
and H
_ce
as low as 1.3 Oe have been obtained at the same acetylene partial pressure. The above results can be explained by the measurement of internal stress and magnetostriction. All the films show compressive stress. However, the stress shows a minimum, about 0.2times10
^-9
dyne/cm
²
with the acetylene partial pressure of 1%, and it increases dramatically for acetylene partial pressure higher than 1%