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International audience; The archetypical antiferroelectric, PbZrO3, is currently attracting a lot of interest, but no consensus can be clearly established on the nature of its ground state as well as on the influence of external stimuli over its physical properties. Here, the antiferroelectric state of 45-nm-thick epitaxial thin films of PbZrO3 is established by observing the characteristic structural periodicity of antiparallel dipoles at the atomic scale, combined with clear double hysteresis of the polarization-electric field response related to antiferroelectric–to–ferroelectric phase transitions. Surprisingly, while the antiferroelectric state is identified as the ground state, temperature-dependent measurements show that a transition to a ferroelectric-like state appears in a large temperature window (100 K). Atomistic simulations further confirm the existence, and provides the origin, of such ferroelectric state in the films. Electric-field-induced ferroelectric transitions are also detected by the divergence of the piezoresponse force microscopy response. Using this technique, we further reveal the signature of a ferroelectric ground state for 4-nm-thick PbZrO3 films. Compared with bulk crystals, these results suggest a more complex competition between ferroelectric and antiferroelectric phases in epitaxial thin films of PbZrO3.

Hafnium-based ferroelectric films, remaining their ferroelectricity down to nanoscale thickness, present a promising application for low-power logic devices and nonvolatile memories. It has been appealing for researchers to reduce the required temperature to obtain the ferroelectric phase in hafnium-based ferroelectric films for applications such as flexible and wearable electronics. In this work, it demonstrates that a remanent polarization (P r) value of >5 μC/cm2 can be obtained in as-deposited Hf0.5Zr0.5O2 (HZO) films that are fabricated by thermal atomic layer deposition (TALD) under low temperature of 250 ℃. The ferroelectric orthorhombic phase (o-phase) in the as-deposited HZO films was detected by scanning transmission electron microscopy (STEM). This low fabrication temperature further extends the compatibility of ferroelectric HZO films to flexible electronics and avoids the cost imposed by following high-temperature annealing treatments.

The main limitations of current methods for synthesizing perovskite oxide (ABO3) nanoparticles (NPs), e.g., the high reagent costs and sophisticated equipment, the long time and high-temperature processing, or multiple post-processing and thermal treatment steps, hamper their full study and potential application. Here, we use a facile low temperature (50°C) chemical bath synthesis and only one annealing step to successfully produce high phase purity and crystalline quality nano-shaped rare-earth-based REMO3 NPs (RE = La, Nd, Sm, Gd; M= Fe, Mn, Al). We also show the versatility of this approach by fabricating La0.7Sr0.3MnO3 solid solution and non-RE-based BiFeO3 perovskite. To assess the potential of the as-prepared REFeO3 and REMnO3 NPs, they are used for photocatalytic degradation of the norfloxacin antibiotic and show high efficiency. We believe this easy, robust, versatile, and general route for synthesizing ABO3-based NPs can be further explored in the vast perovskite family and beyond.

Multiferroic materials have attracted significant research attention due to their technological potential for applications as multifunctional devices. The scarcity of single-phase multiferroics and their low inherent coupling between multiferroic order parameters above room temperature pose a challenge to their further applications. We propose a 3BiFeO3/7BaTiO3 perovskite–perovskite composite that combines ferroelectricity and ferromagnetism. We demonstrate that the sintering temperature can tailor the ferroelectricity and ferromagnetism of the composites. The multiferroicity can be achieved at a low sintering temperature in the composite-like structure ceramics, and its multiferroic properties, especially the ferromagnetism, are superior to those of solid solutions. We also investigate the dynamic evolution of multiferroicity with sintering temperature. We adopt a nano–micro strategy to construct a composite-like microstructure, which results in optimized ferroelectric (1.62 μC cm−2) and ferromagnetic (0.16 emu/g) characteristics at a sintering temperature of 750 °C. We also found experimental evidence of the competition between antiferromagnetic and ferromagnetic interactions in the transition metal cation sublattice. Multiferroic BiFeO3/BaTiO3 composites with combined ferroelectric and ferromagnetic properties have significant potential for various applications.

In materials science, intentional doping has been widely used to improve the properties of a variety of materials. However, such an approach is not yet exploited in the fast-growing field of electrocaloric materials, which represent a serious alternative for next-generation cooling systems. Here we demonstrate with ${\mathrm{Ba}}_{0.9}{\mathrm{Sr}}_{0.1}{\mathrm{Hf}}_{0.1}{\mathrm{Ti}}_{0.9}{\mathrm{O}}_{3}$, an ecofriendly ferroelectric material, that doping with 2% of $\mathrm{Cu}$ introduces defect dipoles into the ferroelectric matrix and results in (i) enhancement of the adiabatic temperature change \ensuremath{\Delta}T by up to 54% while maintaining performance after a large number (up to ${10}^{4}$) of electric field cycles, (ii) suppression of the parasitic irreversibility of \ensuremath{\Delta}T between on-field and off-field states, and (iii) an alternative design of refrigeration cycle with a prepoled sample, allowing a two-field-step process showing both conventional (\ensuremath{\Delta}T g 0) and inverse (\ensuremath{\Delta}T 0) responses when the field is sequentially varied. We also demonstrate that doping significantly increases the energy storage density (by up to 72%). The defect engineering approach therefore offers a path for designing ferroelectrics with improved electrocaloric performances. Beyond ferroelectrics, this strategy could also be promising in other solid-state caloric materials (magnetocalorics, elastocalorics, etc.).

Ultra-thin Hf1-xZrxO2 films have attracted tremendous interest owing to their Si-compatible ferroelectricity arising from polar polymorphs. While these phases have been grown on Si as polycrystalline films, epitaxial growth was only achieved on non-Si substrates. Here we report direct epitaxy of polar phases on Si using pulsed laser deposition enabled via in situ scavenging of the native a-SiOx under ballistic conditions. On Si (111), polar rhombohedral (r)-phase and bulk monoclinic (m-) phase coexist, with the volume of the former increasing with increasing Zr concentration. R-phase is stabilized in the regions with a direct connection between the substrate and the film through the compressive strain provided by an interfacial crystalline c-SiO2 layer., The film relaxes to a bulk m-phase in regions where a-SiOx regrows. On Si (100), we observe polar orthorhombic o-phase coexisting with m-phase, stabilized by inhomogeneous strains at the intersection of monoclinic domains. This work provides fundamental insight into the conditions that lead to the preferential stabilization of r-, o- and m-phases., 18 pages of manuscript, 7 figures

Al-substituted nickel ferrite NiAlxFe2−xO4, where x = (0.00, 0.05, 0.10 and 0.15) synthesized through chemical co-precipitation method were investigated for their structural, morphological, optical and magnetic characterization. Al3+ substitution plays a significant role in the properties of the ferrite nanoparticles. The TGA showed three mass losses, whereas DTA resulted in three endothermic peaks. Rietveld refined XRD revealed the development of single phase cubic spinel with crystallite sizes around 28–36 nm for aluminum substituted samples. TEM and SEM analysis showed the monodispersion and cubic-like nanostructure. The room temperature infra-red spectra showed the features of higher and lower energy bands detected at ν1 ∼589–595 cm−1 and ν2 ∼405–409 cm−1, respectively corresponded to octahedral vibration (O-band) and tetrahedral (T-band) complexes that also verify the creation of spinels ferrites. The Raman spectra showed five Raman active modes (A1g + Eg + 3T2g) which are estimated in the spinel structure. The optical study showed that the compounds have an optical band gap between 1.60 and 1.89 eV. Mossbauer spectra elucidate the nature of the phases and cation distribution. From the hysteresis loop, it is clear that the synthesized samples can be control, for the NiAlxFe2-xO4 nanoferrites. The photocatalytic activity of Al-substituted nickel ferrite were studied based on the degradation of methyl orange as a model compound, where the results showed that NiAl0.15Fe 1.85O4 a good photocatalytic activity.

International audience; We have successfully synthesized and transferred graphene (Gr) monolayers on top of epitaxial mixed valence La0.7Sr0.3CoO3 (LSCO) thin films. Raman spectroscopy reveals that Jahn-Teller (JT) modes associated with the oxygen octahedral distortions usually unobserved for bare LSCO are activated by the deposited graphene. The appearance of these JT modes in the Gr/LSCO heterostructure is attributed to the electronic interactions at the interface between the graphene and the LSCO thin film promoting intermediate spin states of the Co ions. As a result, the magnetic properties of LSCO are affected. Indeed, magnetization measurements show a phase transition at ~135 K which is due to the presence of the graphene while the ferromagnetic transition of bare LSCO films is observed at~200 K. This magnetic phase is confirmed by Raman spectroscopy measurements as a function of temperature revealing a vibrational transition around the same temperature.

Brain‐inspired associative memory is meaningful for pattern recognitions and image/speech processing. Here, a ferroelectric synaptic transistor network is proposed that is capable of associative learning and one‐step recalling of a whole set of data from only partial information. The competition between an external field and the internal depolarization field governs the ferroelectric creep of domain walls and offers each single ferroelectric synapse a full and subfemtojoule‐energy‐cost Hebbian synaptic plasticity, including short‐term memory (STM) to long‐term memory (LTM) transition, and remarkably both spike‐timing‐dependent plasticity (STDP) and spike‐rate‐dependent plasticity (SRDP). Assisted by the third terminal to control the ferroelectric domain dynamics, self‐adaptive coupling between neurons is realized by updating synaptic weight concurrently. Pavlov's dog experiment and multiassociative memories are demonstrated in this ferroelectric synaptic transistor network. Such ferroelectric synaptic transistor network is available for building multilayer neural networks and provides new avenues for associative‐memory information processing.

The temperature-dependent ferroelectric properties of super-tetragonal ${\mathrm{BiFeO}}_{3}$ are investigated using surface-sensitive low-energy electron microscopy (LEEM). We use epitaxial oxide ${\mathrm{BiFeO}}_{3}/{\mathrm{Ca}}_{0.96}{\mathrm{Ce}}_{0.04}{\mathrm{MnO}}_{3}$ bilayers grown by pulsed laser deposition on ${\mathrm{YAlO}}_{3}$ substrates. Ferroelectric, micrometer-scale domains are written by piezoresponse force microscopy and subsequently observed by LEEM from room temperature up to about 950 K. Kelvin probe force microscopy and LEEM spectroscopy reveal that the surface potential is efficiently (g50%) screened by adsorbates that are only released after annealing above 873 $\ifmmode\pm\else\textpm\fi{}$ 50 K in ultrahigh vacuum. The surface structure and chemistry of the ferroelectric thin films are analyzed using scanning transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy, discarding the occurrence of a putative ``skin layer'' effect. While its magnetic and structural transitions were reported in the literature, the true, ferroelectric Curie temperature of super-tetragonal ${\mathrm{BiFeO}}_{3}$ has not been determined so far. Here, we measure a Curie temperature of 930 $\ifmmode\pm\else\textpm\fi{}$ 30 K for the super-tetragonal ${\mathrm{BiFeO}}_{3}$ surface and corroborate it with volume-sensitive, temperature-dependent x-ray diffraction measurements. These results suggest that LEEM can be used as a powerful tool to probe surface charge and ferroelectric transitions in ultrathin films.

International audience; The combination of significant polarization and large light absorption is a challenge in ferroelectric materials. Here we report the optical absorption of BaTiO3 codoped with trivalent and pentavalent transition metal ions replacing the Ti4+ cation, i.e., BaTi1-x(X1/2Y1/2)xO3 (X = Sc, Mn, Fe, Co; Y= Nb, Ta; with x = 0.075). We investigated the optical absorption behavior as a function of different pairs of co-dopants as well as physical properties such as ferroelectricity and piezoelectricity. X-ray diffraction and Raman spectroscopy measurements show that the tetragonality and polar coherence length decrease after co-doping, which affects the ferroelectric properties. It was found that the onset of absorption can decrease down to 1.5 eV, especially for the (Co3+, Nb5+) co-doped samples, which simultaneously exhibit higher polarization than with the other co-doped ions. The measured photoconductivity confirms that the (Co3+, Nb5+) doping has higher absorption than others. Our Density Functional Theory calculations show that codoping inserts intragap levels which are responsible for lowering the energy of optical absorption, which is in full agreement with our experimental observations. This work opens new perspectives for the use of ferroelectrics in optoelectronic devices.

The last few decades have witnessed the rapid development of electronic computers relying on von Neumann architecture. However, due to the spatial separation of the memory unit from the computing processor, continuous data movements between them result in intensive time and energy consumptions, which unfortunately hinder the further development of modern computers. Inspired by biological brain, the in situ computing of memristor architectures, which has long been considered to hold unprecedented potential to solve the von Neumann bottleneck, provides an alternative network paradigm for the next-generation electronics. Among the materials for designing memristors, i.e., nonvolatile memories with multistate tunable resistances, ferroelectric polymers have drawn much research interest due to intrinsic analog switching property and excellent flexibility. In this review, recent advances on artificial synapses based on solution-processed ferroelectric polymers are discussed. The relationship between materials' properties, structural design, switching mechanisms, and systematic applications is revealed. We first introduce the commonly used ferroelectric polymers. Afterward, device structures and the switching mechanisms underlying ferroelectric synapse are discussed. The current applications of organic ferroelectric synapses in advanced neuromorphic systems are also summarized. Eventually, the remaining challenges and some strategies to eliminate non-ideality of synaptic devices are analyzed.

Enabling the light control of complex systems on ultrashort timescales gives rise to rich physics with promising applications. Although crucial, the quantitative determination of both the longitudinal and the shear photoinduced strains still remains challenging. Here, by scrutinizing asymmetric Bragg peaks pairs $(\ifmmode\pm\else\textpm\fi{}h01)$ in ${\mathrm{BiFeO}}_{3}$ using picosecond time-resolved x-ray diffraction experiments, we simultaneously determine the longitudinal and shear strains. Importantly, we reveal a difference in the dynamical response of the longitudinal strain with respect to the shear one due to an interplay of quasilongitudinal and quasitransverse acoustic modes, well reproduced by our model. Finally, we show that the relative amplitude of those strains can be explained only if both thermal and nonthermal processes contribute to the acoustic phonon photogeneration process.

International audience; In-rich InxGa1−xAs epitaxial layers were grown on InP (1 0 0) substrates by a metalorganic vapor phase epitaxy (MOVPE) technique. The effect of Indium (In) composition on the crystalline quality and optical properties are investigated. High resolution X-ray diffraction (HR-XRD) measurement and Raman scattering spectrum are used to evaluate the crystalline quality, the residual strain and dislocation density property. The number of dislocations in the epitaxial layers is found to increase by increasing the Indium content in order to release the stresses due to the epitaxial clamping. Photoluminescence (PL) measurement is used to characterize the optical properties. At 10 K, PL measurements show that the InGaAs band gap redshifts with the indium content. Moreover, the asymmetry at the low-energy side of the PL peak has been attributed to the presence of localized excitons. In all samples, a blue shift of PL peaks is evidenced by increasing the excitation power density, which is in line with the presence of carrier’s localization and non-idealities in this system. Moreover, the temperature-dependence of the PL peak energy displays an unusual red-blue-red shift (S-shaped) behavior when raising the temperature. These observations can be related to the inhomogeneous distribution of indium which gives rise to the appearance of dislocations and other defects which serve as traps for charge carriers. Interestingly, those highly In-content InxGa1−xAs epitaxial layers show PL emission located between 1637 and 1811 nm (depending on In content) and thus might be suitable for in the design of novel heterostructure devices such as short wave infrared (SWIR) detectors.

$\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}/\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ superlattices deposited on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrates are studied using a combination of x-ray diffraction, piezoresponse force microscopy, scanning transmission electron microscopy, transport measurements, and impedance spectroscopy. The superlattices are found to have two inequivalent interfaces resulting from differences in the growth modes for $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ and $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$. X-ray diffraction measurements show that, despite being sandwiched between metallic $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ layers, the ferroelectric layers possess dense nanoscale domains. The observed domain sizes are comparable to those found in ferroelectric-dielectric systems, and they are attributed to the depolarizing field caused by the finite screening length of the $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ interface. The macroscopic capacitance of the ultrathin $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ layers was measured, and its temperature dependence was found to be consistent with permittivity enhancement due to domain wall motion.

Effective Hamiltonian simulations are conducted to unveil the nature of the low-frequency polar modes in the prototype relaxor ferroelectric, $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$. Above the so-called ${T}^{*}$ temperature, only a single soft-mode exists, with its frequency increasing under heating. On the other hand, for temperatures lower than the freezing temperature, this single soft-mode splits into two modes, with one mode slightly changing its low resonant frequency while the other exhibiting a resonant frequency sharply increasing under cooling, in agreement with previous measurements. More importantly, we present evidences that these two modes can be regarded as Goldstone-like and Higgs-like modes, inherent to the Mexican-hat-form of the atomic displacement potential we also reveal here, therefore extending the types of systems exhibiting Higgs-boson characteristics to relaxor ferroelectrics.

Macroscopic polarity and its dynamic response to external electric fields and temperature in the nominally ergodic relaxor phase of pristine lead magnesium niobate crystals and ceramics, Pb(Mg1/3Nb2/3)O3 (PMN), were investigated. Dynamic pyroelectric measurements provide evidence for persistent macroscopic polarity of the samples. Annealing experiments below and above Burns temperature of polarized samples relate this polarity to the presence of polar nano entities and their dynamics. The dc electric field strength required for macroscopic polarization reversal is similar to the amplitude of the ac field where dynamic nonlinear dielectric permittivity reaches maximum. Consequently, the aforementioned maximum is related to the reorientation of polar nano entities. The results question the existence of an ergodic state in PMN below Burns temperature., Comment: 14 pages main text, 5 pages supplementary information

International audience; Multilayer capacitors (MLCs) represent promising electrocaloric (EC) cooling elements because they operate at low voltages, they possess large breakdown fields, they contain inner electrodes that facilitate heat transfer, and they exhibit a macroscopic volume of active EC material. However, almost ten years after they were first suggested as EC elements, the internal heat flow has not been well studied. In this paper, we use an infrared camera to investigate heat flow within representative MLCs of Pb(Mg,Nb)O3, and we achieve good agreement with the results of finite element modelling (FEM) by identifying for the inner electrodes an effective thermal conductivity that represents the limiting factor for heat flow. Increasing the inner electrode thickness by a factor of five would increase heat flow by a factor of 2.6. Our work therefore shows that FEM can play an important role in MLC design for EC applications

Materials possessing multiple states are promising to emulate synaptic and neuronic behaviors. Their operation frequency, typically in or below the GHz range, however, limits the speed of neuromorphic computing. Ultrafast THz electric field excitation has been employed to induce nonequilibrium states of matter, called hidden phases in oxides. One may wonder if there are systems for which THz pulses can generate neuronic and synaptic behavior, via the creation of hidden phases. Using atomistic simulations, we discover that relaxor ferroelectrics can emulate all the key neuronic and memristive synaptic features. Their occurrence originates from the activation of many hidden phases of polarization order, resulting from the response of nanoregions to THz pulses. Such phases further possess different dielectric constants, which is also promising for memcapacitor devices.

This paper deals with the results on the structural, electrical, vibrational and optical properties of LaMn1−xNixO3 (0 ≤ x ≤ 0.3) thin films prepared by the spray pyrolysis technique on glass substrates at 460 °C using (LaCl3·7H2O), (MnCl2·4H2O) and (NiCl2·6H2O) as precursors. First, XRD analysis shows an orthorhombic structure of all prepared thin films. Second, room temperature Raman spectra showed broad and intense bands characteristic of LaMnO3 parent compound modes. An important shift to higher frequencies was observed and attributed to disorder induced by Ni composition and Frenkel defects associated to the formation of vacancy and interstitial oxygen sites. The optical measurements show that the optical band gap energy value varies sparsely in terms of Ni content. On the other hand, the electric conductivity measurements were investigated using the impedance spectroscopy technique in the frequency range 5 Hz–10 MHz at various temperatures (410–500 °C). AC conductivity of LaMn1−xNixO3 thin films is found to follow the Jonsher law. The temperature dependence of the AC conductivity is consistent with the correlated barrier-hopping model with activation energy Ea varying in (0.70–1.29) eV domain. Finally, the magnetic hysteresis loops of such films exhibit obvious ferromagnetic behavior with a high dependency with Ni content particularly the coercivity value (Hc) increases with Ni concentration.

International audience; Chirality, a foundational concept throughout science, may arise at ferromagnetic domain walls 1 22 and in related objects such as skyrmions 2. However, chiral textures should also exist in other types 23 of ferroics such as antiferromagnets for which theory predicts that they should move faster for 24 lower power 3 , and ferroelectrics where they should be extremely small and possess unusual 25 topologies 4,5. Here we report the concomitant observation of antiferromagnetic and electric chiral 26 textures at domain walls in the room-temperature ferroelectric antiferromagnet BiFeO 3. 27 Combining reciprocal and real-space characterization techniques, we reveal the presence of 28 periodic chiral antiferromagnetic objects along the domain walls as well as a priori energetically 29 unfavorable chiral ferroelectric domain walls. We discuss the mechanisms underlying their 30 formation and their relevance for electrically controlled topological oxide electronics and 31 spintronics. 32 33 Metallic ferromagnets have been the elemental bricks of spintronics for the last three decades and 34 continue to hold promises on the basis of non-collinear chiral spin textures such as skyrmions. These 35 topologically protected objects are envisioned to be the future of magnetic data storage thanks to 36 their specific stability, dynamics, and scalability 2. In parallel, antiferromagnets (AFs) are emerging as a 37 new paradigm for spintronics 6. They are intrinsically stable (being insensitive to spurious magnetic 38 fields), scalable (no cross talk between neighbouring memory cells), and fast (switching frequencies 39 in the THz regime). The opportunity of gathering the best of these two worlds and realize 40 "antiferromagnetic skyrmions" is then tremendously appealing but faces at least two major 41 challenges. The first one is to achieve antiferromagnetic chirality and the second one is to identify 42 appropriate control stimuli to create, annihilate and move these chiral objects. 43 On one hand, chirality may naturally emerge at domain walls. The antiferromagnetic domain wall 44 structure is a virtually uncharted territory but this is where translational symmetry is broken and spin 45 rotation favoured. On the other hand, AF manipulation is hampered by the intrinsic lack of net 46 magnetization, which prevents a straightforward magnetic actuation. This fundamental issue may be 47

Since the emergence of memristors (or memristive devices), how to integrate them into arrays has been widely investigated. After years of research, memristor crossbar arrays have been proposed and realized with potential applications in nonvolatile memory, logic and neuromorphic computing systems. Despite the promising prospects of memristor crossbar arrays, one of the main obstacles for their development is the so-called sneak-path current causing cross-talk interference between adjacent memory cells and thus may result in misinterpretation which greatly influences the operation of memristor crossbar arrays. Solving the sneak-path current issue, the power consumption of the array will immensely decrease, and the reliability and stability will simultaneously increase. In order to suppress the sneak-path current, various solutions have been provided. So far, some reviews have considered some of these solutions and established a sophisticated classification, including 1D1M, 1T1M, 1S1M (D: diode, M: memristor, T: transistor, S: selector), self-selective and self-rectifying memristors. Recently, a mass of studies have been additionally reported. This review thus attempts to provide a survey on these new findings, by highlighting the latest research progress realized for relieving the sneak-path issue. Here, we first present the concept of the sneak-path current issue and solutions proposed to solve it. Consequently, we select some typical and promising devices, and present their structures and properties in detail. Then, the latest research activities focusing on single-device structures are introduced taking into account the mechanisms underlying these devices. Finally, we summarize the properties and perspectives of these solutions.

International audience; Bismuth ferrite (BFO) is the drosophila of research in multiferroic materials due to its simultaneous magnetic and electric ordering at room temperature. The unfortunate detail is its antiferromagnetic ordering, which practically cancels magnetization and magnetoelectric coupling of the crystals. To induce finite coupling, dopants have been introduced with a certain success so far. Nanoparticles (NPs) can additionally constrain the formation of the magnetic cycloid in BFO due to size confinement. Doping nanoparticles can thus potentially provide a sizeable magnetization of BFO, making applications in computer memories and hyperthermia cancer treatment feasible. We show that the codoping of BFO NPs by Ba and Mn balances the electrochemical equilibrium, reduces the particle size, and shifts the magnetic phase transition to lower temperatures. The ferroelectric properties are retained and the remanent magnetization is increased by 1 order of magnitude: Bi0.95Ba0.05Fe0.95Mn0.05O3 possesses a remanent magnetization of 0.277 Am2/kg. Our Mössbauer studies reveal that two effects drive this increase: partial destruction of the spin cycloid due to Mn and increased spin canting due to Ba doping inducing local stress fields. This dopant combination and particular concentration improve the effective magnetization value exceptionally well.

International audience; Two-dimensional electron gases (2DEGs) can form at the surface of oxides and semiconductors or in carefully designed quantum wells and interfaces. Depending on the shape of the confining potential, 2DEGs may experience a finite electric field, which gives rise to relativistic effects such as the Rashba spin-orbit coupling. Although the amplitude of this electric field can be modulated by an external gate voltage, which in turn tunes the 2DEG carrier density, sheet resistance and other related properties, this modulation is volatile. Here, we report the design of a "ferroelectric" 2DEG whose transport properties can be electrostatically switched in a nonvolatile way. We generate a 2DEG by depositing a thin Al layer onto a SrTiO 3 single crystal in which 1% of Sr is substituted by Ca to make it ferroelectric. Signatures of the ferroelectric phase transition at 25 K are visible in the Raman response and in the temperature dependences of the carrier density and sheet resistance that shows a hysteretic dependence on electric field as a consequence of ferroelectricity. We suggest that this behavior may be extended to other oxide 2DEGs, leading to novel types of ferromagnet-free spintronic architectures.