Abstract
The functionalities of BiFeO3 -based magnetoelectric multiferroic heterostructures rely on the controlled manipulation of their ferroelectric domains and of the corresponding net in-plane polarization, as this aspect guides the voltage-controlled magnetic switching. Chemical substitution has emerged as a key to push the energy dissipation of the BiFeO3 into the attojoule range but appears to result in a disordered domain configuration. Using non-invasive optical second-harmonic generation on heavily La-substituted BiFeO3 films, it is shown that a weak net in-plane polarization remains imprinted in the pristine films despite the apparent domain disorder. It is found that this ingrained net in-plane polarization can be trained with out-of-plane electric fields compatible with applications. Operando studies on capacitor heterostructures treated in this way show the full restoration of the domain configuration of pristine BiFeO3 along with a giant net in-plane polarization enhancement. Thus, the experiments reveal a surprising robustness of the net in-plane polarization of BiFeO3 against chemical modification, an important criterion in ongoing attempts to integrate magnetoelectric materials into energy-efficient devices.
Highlights
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Magnetoelectric (ME) multifersecond-harmonic generation on heavily La-substituted BiFeO3 films, it is shown that a weak net in-plane polarization remains imprinted in the pristine films despite the apparent domain disorder
BiFeO3, a spontaneously formed ferroelectric stripe-domain configuration facilitates a reliable reversal of the magnetic order by an out-of-plane electric field.[1,7,8]
Summary
Epitaxial BiFeO3 and La0.15Bi0.85FeO3 films with a thickness of 100 nm were grown on SrRuO3-buffered (110)o-oriented singlecrystalline DyScO3 substrates using pulsed laser deposition (see Experimental Section). A fit of the anisotropy of the SHG signal from the La0.15Bi0.85FeO3 films in Figure 1(d) reveals that its angular dependence cannot be properly emulated with the SHG susceptibility components allowed for BiFeO3 in a 71° stripe-domain configuration. We observe a fivefold enhancement of the SHG yield in the switched area with respect to the surrounding pristine state when the optical configuration is set to probe the net polarization of La0.15Bi0.85FeO3 along [110]o, see Figure 2a. When we set the polarization of the ingoing and the emitted light to probe along [110]o, we observe a strong increase in SHG yield after the electric-field training Note that this SHG enhancement is independent of the polarity of the poled state, see Figure S2, Supporting Information. We conclude that the dynamics of the domains observed in the SPM tip-poling experiments in Figure 2 is fully transferable to the device-like architecture of the electrode|La0.15Bi0.85FeO3| electrode capacitor
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