Large electric-field control of perpendicular magnetic anisotropy in strained [Co/Ni] / PZT heterostructures

We present a piezoelectric/ferromagnetic heterostructure with PMA - a Co/Ni multilayer sputtered directly onto a Pb(Zr,Ti)O$_{\mathrm{3}}$ (PZT) substrate. Chemical-mechanical polishing was used to reduce the roughness of PZT plates to below 2 nm \textit{rms}, enabling optimal magnetoelectric coupling via the direct interface between PZT and sputtered Co/Ni films with large PMA ($K_{\mathrm{eff}}$~$=$ (95 \textpm 9 kJ/m$^{\mathrm{3}}))$. We grew the following layer stack: Ta(3)/Pt(2)/[Co(0.15)/Ni(0.6)]$_{\mathrm{x4}}$/Co(0.15)/Pt(2)/Ta(3); numbers in parentheses indicate thicknesses in nm. Applied electric fields up to $+$/- 2 MV/m to the PZT generated 0.05{\%} in-plane compression in the Co/Ni multilayer, enabling a large electric-field reduction of the PMA ($\Delta K_{\mathrm{eff}} \quad \ge $10$^{\mathrm{3}}$ J/m$^{\mathrm{3}})$ and of the coercive field (35{\%}). Our results demonstrate that: (i) heterostructures combining PZT and [Co/Ni] exhibit larger PMA ($K_{\mathrm{eff}}$ \textasciitilde 10$^{\mathrm{5}}$ J/m$^{\mathrm{3}})$ than previous magnetoelectric heterostructures based on Co/Pt and CoFeB, enabling thermally stable hybrid magnetoelectric/spintronic devices only tens of nm in diameter and (ii) electric-field control of the PMA is promising for more energy efficient switching of spintronic devices.