Final Report Summary - ECOMAGICS (Electric Control of Magnetization Dynamics)
The aim of this project was the development of electric field control of magnetization dynamics. In order to implement this “multiferroic” property different hybrid approaches were chosen: (i) the electric field is applied to the surface of an ultrathin ferromagnetic material to dynamically control the magnetic anisotropy. (ii) Propagating strain waves are generated in a piezoelectric substrate and used to drive propagating spin waves in magnetic wires. And (iii) electrical currents in magnetic wires are used to tune the magnetic excitation via the spin Hall and spin wave Doppler effects.
For (i) electric fields are applied to the surface of ultrathin epitaxial ferromagnetic layer structures. We succeeded in electrically controlling the magnetic anisotropy of ultrathin Fe layers. In the analysis we found a large charge trapping contribution to the voltage controlled anisotropy. This effect can be avoided by ac modulation.
(ii) Propagating strain waves are used to drive spin waves in magnetic wires deposited on piezoelectric substrates. We have improved the quality and feature size of the surface acoustic wave transducers to produce mechanical strain waves at up to 10 GHz. We this method propagating spin waves in were excited in films and wires.
(iii) Using analytical models and micro magnetic simulations we improved our understanding of linear non-linear spin wave excitations particularly in the low magnetic bias field regime. We found that the commonly accepted model of Suhl instability processes is actually not valid at low bias fields. Since the spin wave Doppler effect was found not to be large enough to control the non-linear processes we used the spin Hall effect. For heavy metal/ferromagnet bilayer wires we demonstrated the large ac inverse spin Hall effect. On the other hand our time resolve microscopy experiments revealed a disagreement between the magnitude of the inverse spin Hall effect for W and Ta between the inverse spin Hall effect (detected by voltage signal) and the spin Hall effect induced spin transfer torque (detected by time resolved Kerr microscopy).
For (i) electric fields are applied to the surface of ultrathin epitaxial ferromagnetic layer structures. We succeeded in electrically controlling the magnetic anisotropy of ultrathin Fe layers. In the analysis we found a large charge trapping contribution to the voltage controlled anisotropy. This effect can be avoided by ac modulation.
(ii) Propagating strain waves are used to drive spin waves in magnetic wires deposited on piezoelectric substrates. We have improved the quality and feature size of the surface acoustic wave transducers to produce mechanical strain waves at up to 10 GHz. We this method propagating spin waves in were excited in films and wires.
(iii) Using analytical models and micro magnetic simulations we improved our understanding of linear non-linear spin wave excitations particularly in the low magnetic bias field regime. We found that the commonly accepted model of Suhl instability processes is actually not valid at low bias fields. Since the spin wave Doppler effect was found not to be large enough to control the non-linear processes we used the spin Hall effect. For heavy metal/ferromagnet bilayer wires we demonstrated the large ac inverse spin Hall effect. On the other hand our time resolve microscopy experiments revealed a disagreement between the magnitude of the inverse spin Hall effect for W and Ta between the inverse spin Hall effect (detected by voltage signal) and the spin Hall effect induced spin transfer torque (detected by time resolved Kerr microscopy).