Tuning the Dzyaloshinskii-Moriya interaction (DMI) using electric (E)-fields in magnetic devices has opened up new perspectives for controlling the stabilization of chiral spin structures. Recent efforts have used voltage-induced charge redistribution at magnetic/oxides interfaces to modulate the DMI. This approach is attractive for active devices but tends to be volatile, making it energy-demanding. Here we demonstrate nonvolatile E-field manipulation of the DMI by ionic-liquid gating of Pt/Co/HfO2 ultra thin films. The E-field effect on the DMI is linked to the migration of oxygen species from the HfO2 layer into the Co and Pt layers and subsequent anchoring. This effect permanently changes the properties of the material, showing that E-fields can be used not only for local gating in devices but also as a material design tool for post growth tuning of the DMI.
Electric field can tune interfacial magnetism, thus paving the way towards new low power devices using gate voltage. In particular, its effect on skyrmions, which are promising to code information bits, is a critical issue. Here, we first address the effect of electric field on interfacial anisotropy in Pt/Co/AlOx ultrathin trilayers and the possibility to control skyrmion nucleation and annihilation with gate voltage. Then we report the effect of electric field on the interfacial interaction responsible for skyrmions, namely Dzyaloshinskii-Moriya Interaction (DMI). We demonstrate an unprecedented large electric field effect on DMI (βDMI = 600 fJV-1m-1) in Ta/FeCoB/TaOx ultrathin trilayers through Brillouin Light Scattering spectroscopy. Additional Kerr effect observations lead us to propose that electric field could ultimately reverse the sign of DMI, resulting in chirality switch.
Brillouin light scattering (BLS) was conducted on melt-grown ZnO bulk crystals and ZnO thin films grown by pulsed laser deposition. The bulk ZnO crystals presented both longitudinal and transverse bulk acoustic waves. Theoretical calculations agreed well with there being one piezoelectric longitudinal branch and two transverse branches. BLS measurements conducted on ZnO thin films also revealed Rayleigh surface acoustic waves (R-SAW) guided by only the surface of the layer and Sezawa modes, guided by the film thickness. Measurements were conducted for three incidence angles in order to investigate different SAW wave numbers. Higher frequency features were identified as being related to a new class of guided longitudinal (LG) SAW modes which are not usually detected for ZnO thin films. The LG-SAW modes were observed for two incidence angles (θ=45° and 55°) corresponding to frequencies of 17.88 and 20.75 GHz, respectively. BLS measurements enable us to estimate the LG-SAW velocity as 6500 m/s. This value is three times higher than that of the currently used R-SAW. Theoretical simulations were coherent with the presence of LG modes in the ZnO layers. Such LG-SAW modes are promising for the development of novel, higher-speed SAW devices operating in the GHz-band and which could be readily incorporated in Si-based integrated circuitry.
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