Systematic study of the strength of VCMA effect in nanomagnets of small and large strength of spin-orbit interaction

The dependence of anisotropy field and strength of spin-orbit (SO) interaction is systematically studied in $Ta/FeB/MgO,W/FeB/MgO, Ta/FeCoB/MgO, [W/FeB]_{n}/MgO, [Ta/FeB]_{n}/MgO$ nanomagnets. It is found that the polarities of gate-voltage dependence of the anisotropy field $H_{ani}$ and the coefficient $k_{so}$ of SO interaction are opposite in all studied nanomagnets. The magnitudes of the voltage dependence of $H_{ani}$ and $k_{so}$ are comparable in a single-ferromagnetic layer nanomagnet, in which measured strength of SO interaction is small, and in a multilayer -ferromagnetic layer nanomagnet, in which measured strength of SO interaction is large.