Electron Accumulation and Emergent Magnetism in LaMnO3/SrTiO3 Heterostructures

Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched LaMnO3/SrTiO3 (001) heterostructures. Using a combination of element-specific X-ray absorption spectroscopy and dichroism, and first-principles calculations, interfacial electron accumulation and ferromagnetism have been observed within the polar, antiferromagnetic insulator LaMnO3. Our results show that the critical thickness for the onset of electron accumulation is as thin as 2 unit cells (UC), significantly thinner than the observed critical thickness for ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely induced by electron over-accumulation. In turn, by controlling the doping of the LaMnO3, we are able to neutralize the excessive electrons from the polar mismatch in ultrathin LaMnO3 films and thus enable ferromagnetism in films as thin as 3 UC, extending the limits of our ability to synthesize and tailor emergent phenomena at interfaces and demonstrating manipulation of the electronic and magnetic structures of materials at the shortest length scales.Comment: Accepted by Phys. Rev. Let

Spontaneous magnetization above T-C in polycrystalline La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3

In the present work, spontaneous magnetization is observed in the inverse magnetic susceptibility of La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3 compounds above T-C up to a temperature T*. From information gathered from neutron diffraction, dilatometry, and high-field magnetization data, we suggest that T* is related to the transition temperature of the low-temperature (high magnetic field) magnetic phase. In the temperature region between T* and T-C, the application of a magnetic field drives the system from the high-temperature to low-temperature magnetic phases, the latter possessing a higher magnetization

From Architectured Materials to Large-Scale Additive Manufacturing

The classical material-by-design approach has been extensively perfected by materials scientists, while engineers have been optimising structures geometrically for centuries. The purpose of architectured materials is to build bridges across themicroscale ofmaterials and themacroscale of engineering structures, to put some geometry in the microstructure. This is a paradigm shift. Materials cannot be considered monolithic anymore. Any set of materials functions, even antagonistic ones, can be envisaged in the future. In this paper, we intend to demonstrate the pertinence of computation for developing architectured materials, and the not-so-incidental outcome which led us to developing large-scale additive manufacturing for architectural applications

An excursion into the design space of biomimetic architectured biphasic actuators

International audienc

Twisters: an analogy of bilayers for twisting

Benders, such as bilayers, are well-known shape-changing structures which bend upon activation by a stimulus, such as temperature. The objective of this contribution is to propose new shape-changing rod-like structures, referred to as twisters, which twist upon activation. A simple biomimetic design principle based on symmetry considerations is proposed and used to derive a mechanical model. The kinematics of the response of the twister to the simulus is inspired from FEM simulations, and slightly simplified to allow for an analytical resolution of the governing equations. Proposed twisters are shown to first stretch as the stimulus increases until a bifurcation is reached, then, they undergo a mixed stretching-twisting regime. An accurate approximation of the bifurcation point is derived and serves as a guideline for the design of twisters in accordance with chosen specifications. Results are illustrated using twisters with three different behaviours. The methodology can be straightfowardly extended to more complex kinematics and other constitutive laws

Hole-Programmed Superfast Multistep Folding of Hydrogel Bilayers

Two important aspects of actuation behavior of stimuli-responsive hydrogels are the complexity of the shape change and its speed. Here, it is shown that varying the shape of simple polymer bilayers can result in very complex and very fast spontaneous folding. The complexity and high folding rate arise from the choice of the shape and from the presence of inhomogeneous swelling within the thermoresponsive layer entrapped between the top hydrophobic layer and the substrate. In contrast to homogeneous swelling of a freestanding bilayer, which leads to a gradual increase of curvature throughout the whole bilayer, inhomogeneous swelling first results in complete rolling of the periphery of the film, which changes its mechanical properties and affects the subsequent morphing process. Further swelling of the thermoresponsive layer generates more stress that builds up until a buckling threshold is overcome, allowing very fast switching from the flat edge-rolled configuration into a folded one. The research demonstrates how the introduction of holes into actuating bilayers gives rise not only to a novel geometric control over the folding fate of the films but also adds the ability to tune the rate of folding, through the careful selection of hole size, location, and shape