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HfO2-based ferroelectrics show tremendous potential for applications in computing technologies, but questions remain as to what dictates the stabilization of the desired phase. Here, it is demonstrated that the substrate the film is grown on is more influential than factors such as thickness, defect content, and strain. The presence of different possible polymorphs of Hf0.5Zr0.5O2 are observed to vary widely for different substrate materials—with La0.67Sr0.33MnO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and Al2O3 being (more) optimal for stabilizing the ferroelectric-orthorhombic phase. This substrate effect is found to be more influential than any changes observed from varying the film thickness (7.5–60 nm), deposition environment (oxygen vs argon), and annealing temperature (400–600 °C) in vacuum (10−5 Torr). X-ray diffraction and scanning transmission electron microscopy verify the phases present, and capacitor-based studies reveal ferroelectric behavior (or lack thereof) consistent with the phases observed. First-principles calculations suggest that forming oxygen vacancies in Hf0.5Zr0.5O2 lowers its work function, driving electrons away and helping to stabilize the ferroelectric phase. Substrates with a high work function (e.g., La0.67Sr0.33MnO3) facilitate this electron transfer but must also have sufficient ion conductivity to support oxygen-vacancy formation in Hf0.5Zr0.5O2. Together, these observations help clarify key factors essential to the stabilization of HfO2-based ferroelectrics. 

The wider application of spintronic devices requires the development of new material platforms that can efficiently manipulate spin. Bismuthate-based superconductors are centrosymmetric systems that are generally thought to offer weak spin–orbit coupling. Here, we report a large spin–orbit torque driven by spin polarization generated in heterostructures based on the bismuthate BaPb1-xBixO3 (which is in a non-superconducting state). Using spin-torque ferromagnetic resonance and d.c. non-linear Hall measurements, we measure a spin–orbit torque efficiency of around 2.7 and demonstrate current driven magnetization switching at current densities of 4×10^5 A〖cm〗^(-2). We suggest that the unexpectedly large current-induced torques could be the result of an orbital Rashba effect associated with local inversion symmetry breaking in BaPb1-xBixO3. 

Abstract Polar vortices in oxide superlattices exhibit complex polarization topologies. Using a combination of electron energy loss near-edge structure analysis, crystal field multiplet theory, and first-principles calculations, we probe the electronic structure within such polar vortices in [(PbTiO 3 ) 16 /(SrTiO 3 ) 16 ] superlattices at the atomic scale. The peaks in Ti $$L$$ L -edge spectra shift systematically depending on the position of the Ti 4+ cations within the vortices i.e., the direction and magnitude of the local dipole. First-principles computation of the local projected density of states on the Ti $$3d$$ 3 d orbitals, together with the simulated crystal field multiplet spectra derived from first principles are in good agreement with the experiments. 

The AA′-stacked FCGT is a new class of room-temperature Néel-type skyrmion hosting material with C 6v symmetry.