Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet

Abstract

The electric (E) field control of magnetic properties opens the prospects of an alternative to magnetic field or electric current activation to control magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have proven to be particularly sensitive to the influence of an E-field due to the interfacial origin of their anisotropy. In these systems, E-field effects have been recently applied to assist magnetization switching and control domain wall (DW) velocity. Here we report on two new applications of the E-field in a similar material :controlling DW nucleation and stopping DW propagation at the edge of the electrode.The possibility of controlling magnetic properties with an E-field via magneto-electric (ME) effects was initially envisaged in multiferroïcs 1 or magnetic semiconductors 2 . As the majority of these materials loses their ferromagnetic properties at room temperature the recent discovery of

Ferroelectric control of magnetic domains in ultra-thin cobalt layers

“…[5][6][7][8][9] In such layers, a delicate balance between different contributions to the magnetic anisotropy energy (MAE) results in their high sensitivity to the changes of electronic structure at the interface. 10 Thus, a weak change of charge density induced by the electric field at the extremely narrow interface-adjacent layer is sufficient for a substantial change of coercivity, 5-7 T C , 8,9 and magnetic domain kinetics. 11,12 In context of these findings, the ferroelectric/ferromagnetic heterostructures become of interest for electronic elements operational within the conventional temperature range.…”

“…In particular, the MAE varies along the wedge as the oxidation degree changes. 10,17 For optimum oxidation, the MAE shows a maximum and the easy magnetization axis is out of plane. For this experiment, we have selected a region of the wedge near this optimum oxidation state.…”

“…The other implication of the field-effect-tuned MAE is a possibility to change the domain wall (DW) velocity. [10][11][12] In order to directly observe the impact of the ferroelectric gate polarization on the DW propagation, we study a different area in a thinner part of the Al wedge resulting in a more oxidized Co/AlOx interface and greater MAE. Due to the relatively high MAE, the switching is triggered in a very limited number of reversed domains and develops further through the expansion of these domains (as shown in Movies 3 and 4 in the supplementary material 18 ).…”

“…These data were processed using the formalism of Neel-Brown model, which has been previously used for analyzing the thermally-activated nucleation in similar samples with conventional (non-ferroelectric) gate. 10 According to the model, the nucleation probability reads as…”

“…The multilayer consisting of Pt (3 nm)/Co (0.6 nm)/Al (wedge$1.5 nm) stack was deposited by sputtering on Si substrate. 10 Following the deposition, the top Al layer was treated by oxygen plasma in order to reach a partially oxidized AlO x layer. The gradually changing Al thickness along the wedge with the rate of 1 Å /cm leads to the continuous variation of the Co/AlO x interface oxidation degree.…”