The metastable orthorhombic phase of hafnia is generally obtained in polycrystalline films, whereas in epitaxial films its formation has been much less investigated. We have grown Hf0.5Zr0.5O2 films by pulsed laser deposition and the growth window (temperature and oxygen pressure during deposition, and film thickness) for epitaxial stabilization of the ferroelectric phase is mapped. The remnant ferroelectric polarization, up to 24 C/cm 2 , depends on the amount of orthorhombic phase and interplanar spacing and increases with temperature and pressure for a fixed film thickness. The leakage current decreases with an increase in thickness or temperature, or when decreasing oxygen pressure. The coercive electric field (EC) depends on thickness (t) according the EC -t -2/3 scaling, which is observed by the first time in ferroelectric hafnia, and the scaling extends to thickness down to around 5 nm. The proven ability to tailor functional properties of high quality epitaxial ferroelectric Hf0.5Zr0.5O2 films paves the way toward understanding their ferroelectric properties and prototyping devices.

Ferroelectric orthorhombic Hf0.5Zr0.5O2 (HZO) thin films have been stabilized epitaxially on La2/3Sr1/3MnO3/SrTiO3(001) by pulsed laser deposition. The epitaxial orthorhombic films, (111)-oriented and with very flat surface, show robust ferroelectric properties at room temperature. They present a remnant polarization around 20 μC/cm 2 without need of a wake-up process, a large coercive electric field of around 3 MV/cm, an extremely long retention extending well beyond 10 years, and an endurance up to about 10 8 cycles. Such outstanding properties in the nascent research on epitaxial HfO2based ferroelectric films, can pave the way to a better understanding of the effects of orientation, interfaces, strain and defects on ferroelectricity in HfO2.

Monodisperse iron oxide/microporous silica core/shell composite nanoparticles, core(γ‐Fe2O3)/shell(SiO2), with a diameter of approximately 100 nm and a high magnetization are synthesized by combining sol–gel chemistry and supercritical fluid technology. This one‐step processing method, which is easily scalable, allows quick fabrication of materials with controlled properties and in high yield. The particles have a specific magnetic moment (per kg of iron) comparable to that of the bulk maghemite and show superparamagnetic behavior at room temperature. The nanocomposites are proven to be useful as T2 MRI imaging agent. They also have potential to be used in NMR proximity sensing, theranostic drug delivery, and bioseparation.

Doping ferroelectric Hf 0.5 Zr 0.5 O 2 with La is a promising route to improve endurance. However, the beneficial effect of La on the endurance of polycrystalline films may be accompanied by degradation of the retention. We have investigated the endurance-retention dilemma in La-doped epitaxial films. Compared to undoped epitaxial films, large values of polarization are obtained in a wider thickness range, whereas the coercive fields are similar, and the leakage current is substantially reduced. Compared to polycrystalline La-doped films, epitaxial La-doped films show more fatigue but there is not significant wake-up effect and endurance-retention dilemma. The persistent wake-up effect common to polycrystalline La-doped Hf 0.5 Zr 0.5 O 2 films, is limited to a few cycles in epitaxial films. Despite fatigue, endurance in epitaxial La-doped films is more than 10 10 cycles, and this good property is accompanied by excellent retention of more than 10 years. These results demonstrate that wake-up effect and endurance-retention dilemma are not intrinsic in La-doped Hf 0.5 Zr 0.5 O 2 .

Ferroelectric BaTiO3 films with large polarization have been integrated with Si(001) by pulsed laser deposition. High quality c-oriented epitaxial films are obtained in a substrate temperature range of about 300 °C wide. The deposition temperature critically affects the growth kinetics and thermodynamics balance, resulting on a high impact in the strain of the BaTiO3 polar axis, which can exceed 2% in films thicker than 100 nm. The ferroelectric polarization scales with the strain and therefore deposition temperature can be used as an efficient tool to tailor ferroelectric polarization. The developed strategy overcomes the main limitations of the conventional strain engineering methodologies based on substrate selection: it can be applied to films on specific substrates including Si(001) and perovskites, and it is not restricted to ultrathin films.