Thickness Dependence of Magnetic Anisotropy and Damping in Sputter Deposited CoFeB Thin Films

We investigated the uniaxial magnetic anisotropy and magnetic damping of sputter deposited CoFeB thin films in a wide range of thicknesses with ferromagnetic resonance technique. As the thickness of CoFeB film (t(CFB)) is increased from 5 to 90 nm, a strong increase in magnetic anisotropy is observed. This is understood in terms of increased bulk contribution to anisotropy induced by the oblique deposition. On the other hand, the study shows an inverse scaling of intrinsic Gilbert damping constant (alpha) with t(CFB). A lowest alpha value of 0.0029 +/- 0.0007 is reported for 90 nm CoFeB thickness. The study provides essential information on precessional magnetization dynamics of CoFeB thin films which are desirable in number of promising applications in various spintronic devices.