Strain-induced modulation of perpendicular magnetic anisotropy in Ta/CoFeB/MgO structures investigated by ferromagnetic resonance

We demonstrate strain-induced modulation of perpendicular magnetic anisotropy (PMA) in (001)-oriented [Pb(Mg1/3Nb2/3)O-3]((1-x))-[PbTiO3](x) (PMN-PT) substrate/Ta/CoFeB/MgO/Ta structures using ferromagnetic resonance (FMR). An in-plane biaxial strain is produced by applying voltage between the two surfaces of the PMN-PT substrate, and is transferred to the ferromagnetic CoFeB layer, which results in tuning of the PMA of the CoFeB layer. The strain-induced change in PMA is quantitatively extracted from the experimental FMR spectra. It is shown that both first and second-order anisotropy terms are affected by the electric field, and that they have opposite voltage dependencies. A very large value of the voltage-induced perpendicular magnetic anisotropy modulation of similar to 7000 fJ/V.m is obtained through this strain-mediated coupling. Using this FMR technique, the magnetostriction coefficient lambda is extracted for the ultrathin 1.1 nm Co20Fe60B20 layer, and is found to be 3.7 x 10(-5), which is approximately 4 times larger than the previously reported values for CoFeB films thicker than 5 nm. In addition, the effect of strain on the effective damping constant (alpha(eff)) is also studied and no obvious modulation of the alpha(eff) is observed. The results are relevant to the development of CoFeB-MgO magnetic tunnel junctions for memory applications. (C) 2015 AIP Publishing LLC.