Influence of capping layers on CoFeB anisotropy and damping

Abstract

Magnetic behavior of CoFeB at various thicknesses ranging from 2 nm to 8 nm capped with different materials, such as MgO, Ta, Ru, and V have been studied. The films were sputter-deposited and subsequently characterized by magnetometry and broadband ferromagnetic resonance (FMR). There are magnetically dead layers at the interface observed with Ru and Ta capping layers, while MgO and V have almost no effect on the magnetization of the CoFeB. As the ferromagnetic layer is made thinner, the effective magnetization decreases, indicating an interfacial perpendicular anisotropy. Particularly in the case of MgO, V/Ru, and V/Ta capping layers, interfacial perpendicular anisotropy is induced in CoFeB, and the Gilbert damping parameter is also reduced. The origin of this perpendicular magnetic anisotropy (PMA) is understood to be caused by the interface anisotropy between the free layer and the capping layer. The effect of post-deposition annealing and CoFeB thickness on the anisotropy and damping of V/Ta capped samples are reported. Doping CoFeB with vanadium (V) greatly reduced the 4πMs and 4πMeff values, resulting in an effective increase in the PMA.

Transient enhancement of magnetization damping in CoFeB film via pulsed laser excitation

“…11,12 In addition, some other factors, such as thickness, capping layer, and magnetic anisotropy, affect the damping constant as well. 10,13,14 When the thickness of ferromagnetic (FM) layers is sufficiently thin, the spin current generated by the FM layer will flow into the adjacent layer, which increases the electron scattering rate and thus enhances the damping values. In recent years, a powerful pump-probe technique (the time-resolved magneto-optical Kerr effect, TRMOKE) is employed to obtain the damping constant, which is to some extent equal to the conventional ferromagnetic resonance (FMR).…”

“…[7][8][9][10] The increase in damping values can be caused by several possible mechanisms. It is reported that Gilbert damping intrinsically originates from the spin orbital interaction and is proportional to n 2 =W, where n is the spin orbital coupling energy and W is the d-band width.…”

The effect of growth sequence on magnetization damping in Ta/CoFeB/MgO structures

“…Meanwhile, according to the Elliott-Yafet relaxation mechanism, the magnetization damping experiences a substantial increase when B and Ta atoms are inside CoFe, originating from a scatter of electrons [34,35]. Recently, it was demonstrated that the MgO interface suppresses the spin-pumping effect in MgO/FeB/MgO/Ta structures [4,36], and the CoFeB/Ta interface plays an important role in enhancing the [37]. This means that ' of the CoFeB/MgO interface is negligibly small when compared with that of the CoFeB/Ta interface.…”

Magnetic tunnel junctions for magnetic field sensor by using CoFeB sensing layer capped with MgO film

“…Recently, MTJs with MgO capping layers for memory cells have been suggested for making PMA enlarge both the top and bottom interfaces with MgO films in CoFeB free layers. [5][6][7][8][9] In the current study, we evaluate the MTJ structure of a CoFeB sensing layer capped with an MgO film to obtain two interfaces of MgO/CoFeB exhibiting interfacial PMA in order to improve the controllability of the characteristics in MTJs for magnetic field sensors. EXPERIMENT We used MTJs with Ta/Ru (1 nm)/PtMn (15 nm)/CoFe (2 nm)/Ru (0.9 nm)/CoFeB (2.3 nm)/MgO (t barrier nm)/CoFeB (t CoFeB )/MgO (t cap nm)/Ta structures in the experiment.…”