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Funder: NNSA's Laboratory Directed Research and Development Program, Advancement of information technology requires low power, high speed, and large capacity non‐volatile memory. Memristors have potential applications for not only information storage but also neuromorphic computation. Memristive devices are mostly focused on the use of binary oxides as the resistive switching materials. On the other hand, polarization assisted memristive devices based on ternary ferroelectric oxides are attracting more attention due to their unique switching properties. However, the underlying switching mechanisms and the current–voltage rotation direction are still not fully understood yet. By comparing stoichiometric BaTiO3, BiFeO3, and Bi1‐ x FeO3‐ δ ferroelectric memristors with different cation stoichiometry, it is found that off‐stoichiometry‐induced traps can play a critical role in controlling the ferroelectric memristive switching behavior. Ferroelectrics with slight off‐stoichiometry show greatly enhanced switching properties, and the switching on/off ratio is mainly determined by the trap energy levels and concentrations. The rotation direction of current–voltage hysteresis loop is affected by the defects, which can be controlled by synthesis and power dissipation. These findings provide insight in understanding the role of defects in ferroelectric memristors and offer guidance to design ferroelectric memristors with enhanced performance.

Two-dimensional (2D) materials with robust ferromagnetic behavior have attracted great interest because of their potential applications in next-generation nanoelectronic devices. Aside from graphene and transition metal dichalcogenides, Bi-based layered oxide materials are a group of prospective candidates due to their superior room-temperature multiferroic response. Here, an ultrathin Bi3Fe2Mn2O10+δ layered supercell (BFMO322 LS) structure was deposited on an LaAlO3 (LAO) (001) substrate using pulsed laser deposition. Microstructural analysis suggests that a layered supercell (LS) structure consisting of two-layer-thick Bi–O slabs and two-layer-thick Mn/Fe–O octahedra slabs was formed on top of the pseudo-perovskite interlayer (IL). A robust saturation magnetization value of 129 and 96 emu cm−3 is achieved in a 12.3 nm thick film in the in-plane (IP) and out-of-plane (OP) directions, respectively. The ferromagnetism, dielectric permittivity, and optical bandgap of the ultrathin BFMO films can be effectively tuned by thickness and morphology variation. In addition, the anisotropy of all ultrathin BFMO films switches from OP dominating to IP dominating as the thickness increases. This study demonstrates the ultrathin BFMO film with tunable multifunctionalities as a promising candidate for novel integrated spintronic devices.

Materials with magneto-optic coupling properties are highly coveted for their potential applications ranging from spintronics and optical switches to sensors. In this work, a new, three-phase Au-Fe-La0.5Sr0.5FeO3 (LSFO) hybrid material grown in a vertically aligned nanocomposite (VAN) form has been demonstrated. This three-phase hybrid material combines the strong ferromagnetic properties of Fe and the strong plasmonic properties of Au and the dielectric nature of the LSFO matrix. More interestingly, the immiscible Au and Fe phases form Au-encapsulated Fe nanopillars, embedded in the LSFO matrix. Multifunctionalities including anisotropic optical dielectric properties, plasmonic properties, magnetic anisotropy, and room-temperature magneto-optic Kerr effect coupling are demonstrated. The single-step growth method to grow the immiscible two-metal nanostructures (i.e., Au and Fe) in the complex hybrid material form opens exciting new potential opportunities for future three-phase VAN systems with more versatile metal selections.

Oxide-oxide-based vertically aligned nanocomposites (VANs) have demonstrated a new material platform for enhanced and/or combined functionalities because of their unique vertical geometry and strain coupling. Various factors contribute to the growth of VANs, including deposition parameters, phase composition, phase ratios, crystallography, etc. In this work, substrate strain effects are explored through growing a two-phase oxide-oxide La0.7Sr0.3MnO3 (LSMO):NiO system, combining antiferromagnetic NiO and ferromagnetic LSMO, on various substrates with different lattice parameters. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and magnetic property measurements all suggest that substrate strain plays a critical role in the epitaxial growth of a VAN structure and their two-phase separation, and thus results in different physical properties. This work sheds light on the fundamental nucleation and growth mechanisms of the two-phase VAN systems and the effects of substrate strain on the overall orientation and growth quality of the VAN films.

Magneto-optical (MO) coupling incorporates photon-induced change of magnetic polarization that can be adopted in ultrafast switching, optical isolators, mode convertors, and optical data storage components for advanced optical integrated circuits. However, integrating plasmonic, magnetic, and dielectric properties in one single material system poses challenges since one natural material can hardly possess all these functionalities. Here, co-deposition of a three-phase heterostructure composed of a durable conductive nitride matrix with embedded core-shell vertically aligned nanopillars, is demonstrated. The unique coupling between ferromagnetic NiO core and atomically sharp plasmonic Au shell enables strong MO activity out-of-plane at room temperature. Further, a template growth process is applied, which significantly enhances the ordering of the nanopillar array. The ordered nanostructure offers two schemes of spin polarization which result in stronger antisymmetry of Kerr rotation. The presented complex hybrid metamaterial platform with strong magnetic and optical anisotropies is promising for tunable and modulated all-optical-based nanodevices.

Metal-free plasmonic metamaterials with wide-range tunable optical properties are highly desired for various components in future integrated optical devices. Designing a ceramic-ceramic hybrid metamaterial has been theoretically proposed as a solution to this critical optical material demand. However, the processing of such all-ceramic metamaterials is challenging due to difficulties in integrating two very dissimilar ceramic phases as one hybrid system. In this work, an oxide-nitride hybrid metamaterial combining two highly dissimilar ceramic phases, i.e., semiconducting weak ferromagnetic NiO nanorods and conductive plasmonic TiN matrix, has been successfully integrated as a unique vertically aligned nanocomposite form. Highly anisotropic optical properties such as hyperbolic dispersions and strong magneto-optical coupling have been demonstrated under room temperature. The novel functionalities presented show the strong potentials of this new ceramic-ceramic hybrid thin film platform and its future applications in next-generation nanophotonics and magneto-optical integrated devices without the lossy metallic components.

Ferromagnetic nanostructures with strong anisotropic properties are highly desired for their potential integration into spintronic devices. Several anisotropic candidates, such as CoFeB and Fe–Pt, have been previously proposed, but many of them have limitations such as patterning issues or thickness restrictions. In this work, Co–BaZrO3 (Co–BZO) vertically aligned nanocomposite (VAN) films with tunable magnetic anisotropy and coercive field strength have been demonstrated to address this need. Such tunable magnetic properties are achieved through tuning the thickness of the Co–BZO VAN structures and the aspect ratio of the Co nanostructures, which can be easily integrated into spintronic devices. As a demonstration, we have integrated the Co–BZO VAN nanostructure into tunnel junction devices, which demonstrated resistive switching alluding to Co–BZO's immense potential for future spintronic devices.

Ferromagnetic nanostructures with strong anisotropic properties are highly desired for their potential integration into spintronic devices. Several anisotropic candidates, such as CoFeB and Fe-Pt, have been previously proposed, but many of them have limitations such as patterning issues or thickness restrictions. In this work, Co-BaZrO

Room-temperature ferromagnetic materials with perpendicular magnetic anisotropy are widely sought after for spintronics, magnetic data storage devices, and stochastic computing. To address this need, a new Fe-BaTiO3 vertically aligned nanocomposite (VAN) has been fabricated—combining both the strong room-temperature ferromagnetic properties of Fe nanopillars and the strong room-temperature ferroelectric properties of the BaTiO3 matrix. Furthermore, the Fe-BaTiO3 VAN allows for highly anisotropic magnetic properties with tunable magnetization and coercivity. In addition, to demonstrate the multiferroic properties of the Fe-BaTiO3 system, the new metal-oxide hybrid material system has been incorporated in a multilayer stack. This new multiferroic VAN system possesses great potential in magnetic anisotropy and property tuning and demonstrates a new material family of oxide-metal hybrid systems for room-temperature multiferroic material designs.