Interfacial Dzyaloshinskii–Moriya Interaction, Perpendicular Magnetic Anisotropy, and Damping in CoFeB-/Oxide-Based Systems

Perpendicular magnetic anisotropy (PMA), spin pumping-induced damping, and interfacial Dzyaloshinskii–Moriya interaction (iDMI), which are spin–orbit coupling-related phenomena of utmost importance for applications, were experimentally investigated in as-grown and 225 °C annealed CoFeB/PtO
_x
, CoFeB/TaO
_x
, and Ta/CoFeB/TaO
_x
systems by means of vibrating sample magnetometry, microstrip ferromagnetic resonance, and Brillouin light scattering techniques. By varying Co
₈
Fe
₇₂
B
₂₀
(CoFeB) thickness in the range of 0.8–10 nm, the effect of Ta buffer layer on anisotropy and damping was first studied, where a large surface magnetic anisotropy (
$K_{s}=2.1\,\,\pm \,\,0.16$
erg/cm
²
) was measured in the unbuffered CoFeB/TaO
_x
(0.8 nm) system most likely due to their higher roughness induced by the substrate.
$K_{s}$
degrades significantly for CoFeB film thickness below 2 nm where spontaneous perpendicular magnetization was found to be impossible without Ta buffer layer. PMA, iDMI, and damping of as-deposited and 225 °C annealed CoFeB (1.5 nm)/PtO
_x
systems were measured as a function of PtO
_x
thickness in the range of 0.7–1.6 nm. Their strong dependence versus the PtO
_x
thickness was attributed to the decrease of the magnetic dead layer as PtO
_x
thickness increases. Linear dependence of damping versus PMA constant was obtained, confirming their relation with the spin–orbit coupling. Moreover, annealing increases PMA and the effective mixing conductance probably due to the enhancement of the CoFeB crystal structure and interfaces.