  Magnetic anisotropy, spin wave (SW) excitation and exchange stiffness
constant of amorphous FeTaC ($d$ = 20-200 nm) films were studied as a function
of thickness using micro-strip ferromagnetic resonance (MS-FMR) technique. The
MS-FMR spectra for in-plane applied magnetic field show the presence of uniform
precessional mode ($n$ = 0) along with first perpendicular standing spin wave
(PSSW) mode ($n$ = 1) especially for $d$ = 50, 100 and 200 nm films. The
angular ($\varphi_{H}$) dependence of resonance field ($H_{r}$) and magnetic
field dependence of resonance frequencies ($f_{r}$) in planar configuration for
the uniform and PSSW modes were modeled successfully by using dispersion
relation which arises from a combination of exchange and dipolar interactions.
The relevant parameters such as saturation magnetization ($4\pi M_{S}$),
uniaxial anisotropic constant ($K_{u}$), $g$-factor, and exchange stiffness
constants ($A_{ex}$) are estimated for different FeTaC film thickness. $A_{ex}$
is found to increase from 1.52(4)$\times$10$^{-7}$ to 5.0(5)$\times$10$^{-6}$
erg/cm as the thickness of film increases from 50 to 200 nm, possibly due to
surface pinning effect or significant inhomogeneity especially at higher
thickness films.
