Resistive switching, a behavior found in many oxide materials, has the potential to enable emerging computer hardware technologies and architectures. We present resistive switching devices fabricated from epitaxial brownmillerite SrFeO2.5 films with two distinct film orientations, wherein facile oxygen ion diffusion planes are aligned parallel (in-plane) and perpendicular (out-of-plane) with the electrodes. SrFeO2.5 films were grown on (001) oriented Nb:SrTiO3 to enable high-quality interfaces and future integration with Si CMOS technologies. Post-growth vacuum annealing and growth pressure were used to control film orientations, as confirmed by transmission electron microscopy and x-ray diffraction measurements. Films grown with diffusion planes oriented in-plane had oxygen-rich, perovskite-like nanodomains spread throughout the film, and fabricated devices exhibited worse switching consistency and more stochasticity. In contrast, films grown with diffusion planes oriented out-of-plane had a more uniform oxygen-rich perovskite interfacial layer above the bottom electrode, and devices built from this film orientation showed significant statistical improvements in switching voltages and cycling consistency.

Rare-earth nickelates exhibit valuable behavior for neuromorphic computing at low temperature: Building blocks for biologically inspired microelectronic neurons like electrically driven insulator-metal transitions (IMTs), negative differential resistance, and self-oscillations have been shown up to 230 K for SmNiO3 and NdNiO3. EuNiO3 raises the IMT far above room temperature (460 K) but high-quality thin films are challenging to synthesize. Here, we explore the epitaxial stabilization of EuNiO3 using pulsed laser deposition. X-ray diffraction reciprocal space maps, x-ray absorption spectroscopy, and transmission electron microscopy show that higher growth temperature (800 degrees C) reduces oxygen vacancy concentrations in EuNiO3. Pseudomorphic EuNiO3 is demonstrated on both SrLaAlO4 and NdGaO3 substrates, and LaNiO3 buffer layers are incorporated to facilitate future vertical device fabrication. In contrast to bulk thermodynamic predictions, the greater oxidation and crystallinity at higher temperature we observe indicates that epitaxial substrates can stabilize EuNiO3 at O-2 pressures less than 1 atm. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

The effect of oxygen reduction on the magnetic properties of LaFeO3−δ (LFO) thin films was studied to better understand the viability of LFO as a candidate for magnetoionic memory. Differences in the amount of oxygen lost by LFO and its magnetic behavior were observed in nominally identical LFO films grown on substrates prepared using different common methods. In an LFO film grown on as-received SrTiO3 (STO) substrate, the original perovskite film structure was preserved following reduction, and remnant magnetization was only seen at low temperatures. In a LFO film grown on annealed STO, the LFO lost significantly more oxygen and the microstructure decomposed into La- and Fe-rich regions with remnant magnetization that persisted up to room temperature. These results demonstrate an ability to access multiple, distinct magnetic states via oxygen reduction in the same starting material and suggest LFO may be a suitable materials platform for nonvolatile multistate memory.

The magnetic structure and properties were measured in a compositionally complex perovskite manganite possessing local spin disorder on the A-site and found to be similar to an undisordered control.

High-temperature superconductivity is reported in a series of compositionally-complex cuprates with varying degrees of size and spin disorder. Three compositions of Y-site alloyed YBa$_2$Cu$_3$O$_{7-x}$, i.e., (5Y)BCO, were prepared using solid-state methods with different sets of rare earth ions on the Y-site. Synchrotron X-ray diffraction and energy-dispersive X-ray spectroscopy confirm these samples have high phase-purity and homogeneous mixing of the Y-site elements. The superconducting phase transition was probed using electrical resistivity and AC magnetometry measurements, which reveal the transition temperature, T$_C$, is greater than 91 K for all series when near optimal oxygen doping. Importantly, these T$_C$ values are only $\approx$1$\%$ suppressed relative to pure YBCO (T$_C$ = 93 K). This result highlights the robustness of pairing in the YBCO structure to specific types of disorder. In addition, the chemical flexibility of compositionally-complex cuprates allows spin and lattice disorder to be decoupled to a degree not previously possible in high-temperature superconductors. This feature makes compositionally-complex cuprates a uniquely well-suited materials platform for studying proposed pairing interactions in cuprates.

The chips used in modern electronic devices are mainly manufactured and packaged by Outsourced Semiconductor Assembly and Test (OSAT) facilities and are potentially vulnerable to hardware attacks. Due to the complexity of the global supply chain, it is difficult to track the full fabrication process by the foundries or the intellectual property (IP) owners. Additionally, the design for fabricating and packaging the chip made by IP owners remains the same and visible throughout the process. Hence, this design can be seen by every entity in the supply chain using physical inspection techniques, making it vulnerable if any adversaries are present in the supply chain. Security threats such as IP piracy, overbuilding, reverse engineering, and counterfeiting are thus possible by potential adversaries in the supply chain. These attacks have become an increasing concern in the world of trusted microelectronics as supply chain globalization continues to develop. Several security methods have already been developed to protect and detect such threats until they become embedded into sensitive systems, such as logic locking, obfuscating, physically unclonable functions (PUF), and hardware metering. However, these existing prevention methods have their limitations or are not applicable to all devices. In general, only a few existing methods make use of the inherent characteristics of electronic devices and materials to provide reliable security. Hence, novel security and assurance strategies with minimal changes or modifications in the fabrication of the system circuit are urgently required. This paper proposes a novel technique of obfuscation and locking using a reconfigurable nano-electromechanical system (NEMS) based advanced package throughout the supply chain. Using this novel technique, the netlist/golden design for heterogeneously integrated devices will be hidden from malicious adversaries, and the IP designer will have control of its design until it reaches the end-user.

Non-collinear antiferromagnets (AFMs) are an exciting new platform for studying intrinsic spin Hall effects (SHEs), phenomena that arise from the materials' band structure, Berry phase curvature, and linear response to an external electric field. In contrast to conventional SHE materials, symmetry analysis of non-collinear antiferromagnets does not forbid non-zero longitudinal and out-of-plane spin currents with x ̂ , z ̂ $\hat{x},\hat{z}$ polarization and predicts an anisotropy with current orientation to the magnetic lattice. Here, multi-component out-of-plane spin Hall conductivities σ xz x , $\sigma _{{\rm{xz}}}^{\rm{x}},$ σ xz y , σ xz z $\sigma _{{\rm{xz}}}^{\rm{y}},\ \sigma _{{\rm{xz}}}^{\rm{z}}$ are reported in L12 -ordered antiferromagnetic PtMn3 thin films that are uniquely generated in the non-collinear state. The maximum spin torque efficiencies (ξ  = JS  /Je  ≈ 0.3) are significantly larger than in Pt (ξ  ≈  0.1). Additionally, the spin Hall conductivities in the non-collinear state exhibit the predicted orientation-dependent anisotropy, opening the possibility for new devices with selectable spin polarization. This work demonstrates symmetry control through the magnetic lattice as a pathway to tailored functionality in magnetoelectronic systems.

Micro-electro-mechanical systems (MEMS) and sensors are employed in numerous industries including automotive, medical, and communications, and they are at the core of sophisticated new features in the next generation of cellphones and wearables. The use of MEMS in consumer electronics is projected to develop further as their power consumption needs and form factors continue to improve and now satisfy many consumers application demands. However, the incorporation of MEMS into new applications poses security and reliability risks for heterogeneously integrated systems. Heterogeneous integration (HI) improves the functionality and operating capabilities of electronic devices by integrating individually fabricated components into a higher-level assembly. The inclusion of MEMS in HI increases the complexity of the electronics supply chain, making it vulnerable to a multitude of adversary threats. A rogue employee, for instance, might implant an active or passive hardware Trojan and exploit a denial of service (DoS) attack in the chip during the design and/or fabrication process. This study will first provide a detailed review of the MEMS and sensor-based heterogeneous integrated circuit applications, followed by an assessment of HI's potential security and reliability vulnerabilities in critical applications. Finally, we will provide insights to multiple physical-based inspection [2] techniques for assessment and authentication of HI electronics.

The relaxation mechanism of Si1-xGex/Si heterostructures subjected to pulsed laser melting was investigated by probing the pulsed laser induced epitaxy (PLIE) regime of undoped 20 nm Si0.5Ge0.5/Si thin films. The pseudomorphic “critical thickness” and evolution of bi-layer formation was determined as a function of average Ge concentration of the films via quantitative analysis of (004) HRXRD rocking curves. Comparison of pseudomorphic thicknesses alongside SIMS analysis reveals a “dynamic critical Ge concentration” of 27-30% Ge as the PLIE limit for pseudomorphic growth that is independent of average Ge concentration of the films. Plan-view weak-beam dark-field imaging revealed that surface dislocation half-loops are the primary strain relieving defects that reach concentrations on the order of 1010 cm−2. It is theorized that quasi-cellular solidification leads to lateral Ge segregation, creating nm scale localized regions of Ge pile-up and stress concentration. The morphology of the liquid/solid interface along with stress localization is what allows for the dislocation half-loop to be the primary strain relieving defect, with <110> edge defects acting as secondary. These results are important for understanding the conditions and strategies necessary to utilize pulsed laser melting to its fullest potential in applications towards pMOS source/drain contact engineering.

Bi2Se3 is a prototypical topological insulator, which has a small bandgap (∼0.3 eV) and topologically protected conducting surface states. This material exhibits quite strong thermoelectric effects. Here, we show in a mechanically exfoliated thick (∼100 nm) nanoflake device that we can measure the energy dependent optical absorption through the photothermoelectric effect. Spectral signatures are seen for a number of optical transitions between the valence and conduction bands, including a broad peak at 1.5 eV, which is likely dominated by bulk band-to-band optical transitions but is at the same energy as the well-known optical transition between the two topologically protected conducting surface states. We also observe a surprising linear polarization dependence in the response of the device that reflects the influence of the metal contacts.

In article number 2001324, the authors report the achievement of strong ferromagnetism in atomically thin cobaltite by local structural modification, where a surprisingly large magnetic moment and Curie temperature are observed. Thus, a strategy for creating functional quantum heterostructures by exploiting atomic interface engineering is demonstrated.

The topological kagome metal CoSn hosts orbital-selective Dirac bands and very flat bands near the Fermi energy that lead to a range of exotic phenomena, such as fractional quantum Hall states. In this work, we report the synthesis of high-quality epitaxial (0001) CoSn films by magnetron sputtering. Comprehensive structural characterizations demonstrate high crystalline quality with low disorder, sharp interfaces, and a smooth surface. Complementary magnetic and transport properties show a paramagnetic, metallic ground state as seen in bulk. Our work creates a synthetic foundation to investigate and utilize rich topological physics in CoSn thin films and heterostructures.

Low-dimensional quantum materials that remain strongly ferromagnetic down to monolayer thickness are highly desired for spintronic applications. Although oxide materials are important candidates for the next generation of spintronics, ferromagnetism decays severely when the thickness is scaled to the nanometer regime, leading to deterioration of device performance. Here, a methodology is reported for maintaining strong ferromagnetism in insulating LaCoO3 (LCO) layers down to the thickness of a single unit cell. It is found that the magnetic and electronic states of LCO are linked intimately to the structural parameters of adjacent "breathing lattice" SrCuO2 (SCO). As the dimensionality of SCO is reduced, the lattice constant elongates over 10% along the growth direction, leading to a significant distortion of the CoO6 octahedra, and promoting a higher spin state and long-range spin ordering. For atomically thin LCO layers, surprisingly large magnetic moment (0.5 μB /Co) and Curie temperature (75 K), values larger than previously reported for any monolayer oxides are observed. The results demonstrate a strategy for creating ultrathin ferromagnetic oxides by exploiting atomic heterointerface engineering, confinement-driven structural transformation, and spin-lattice entanglement in strongly correlated materials.

Topology and strong electron correlations are crucial ingredients in emerging quantum materials, yet their intersection in experimental systems has been relatively limited to date. Strongly correlated Weyl semimetals, particularly when magnetism is incorporated, offer a unique and fertile platform to explore emergent phenomena in novel topological matter and topological spintronics. The antiferromagnetic Weyl semimetal Mn3Sn exhibits many exotic physical properties such as a large spontaneous Hall effect and has recently attracted intense interest. In this work, we report synthesis of epitaxial Mn3+x Sn1-x films with greatly extended compositional range in comparison with that of bulk samples. As Sn atoms are replaced by magnetic Mn atoms, the Kondo effect, which is a celebrated example of strong correlations, emerges, develops coherence, and induces a hybridization energy gap. The magnetic doping and gap opening lead to rich extraordinary properties, as exemplified by the prominent DC Hall effects and resonance-enhanced terahertz Faraday rotation.

Storing information in magnetic recording technologies requires careful optimization of the recording media’s magnetic properties. For example, heat-assisted magnetic recording (HAMR) relies on a prerecording heating step that momentarily lowers the coercivity of the ferromagnetic recording media, and thereby decreases the energy expenditure for each writing operation. However, this process currently requires local temperature increases of several hundred Kelvins, which in turn can cause heat spreading, damage the write head, and limit recording rates. Here, we describe a general mechanism for dramatically tuning the coercivity of ferromagnetic films over small temperature ranges, by coupling them to an adjacent layer that undergoes a structural phase transition with large volume changes. The method is demonstrated in Ni/FeRh bilayers where the Ni layer was deposited at 300 K and 523 K, above and below the FeRh metamagnetic transition at 370 K. When the Ni layer is grown at high temperatures, the 1% FeRh lattice expansion relative to room temperature alters the Ni’s crystallographic texture during growth and leads to a 500% increase in coercivity upon cooling through the FeRh’s metamagnetic transition. Our analysis suggests this effect is related to domain wall pinning across grain boundaries with different orientations and strain states. This work highlights the promise of thermally tuning the coercivity of ferromagnetic materials through structural coupling to underlying films that could enable simplified heatsink designs and expand the selection of materials compatible with HAMR.

The topological kagome magnet (TKM) Fe3Sn2 exhibits unusual topological properties, flat electronic bands, and chiral spin textures, making it an exquisite materials platform to explore the interplay between topological band structure, strong electron correlations, and magnetism. Here we report the synthesis of high-quality epitaxial (0001) Fe3Sn2 films with large intrinsic anomalous Hall effect close to that measured in bulk single crystals. In addition, we measured a large, anisotropic anomalous Nernst coefficient S-yx of 1.26 mu VK-1, roughly 2-5 times greater than that of common ferromagnets, suggesting the presence of Berry curvature sources near the Fermi level in this system. Crucially, the realization of high-quality Fe3Sn2 films opens the door to explore emergent interfacial physics and create novel spintronic devices based on TKMs by interfacing Fe3Sn2 with other quantum materials and by nanostructure patterning.

Controlling changes in magnetic anisotropy across epitaxial film interfaces is an important prerequisite for many spintronic devices. For the canonical dilute magnetic semiconductor GaMnAs, magnetic anisotropy is highly tunable through strain and doping, making it a fascinating model system for exploration of anisotropy control in a carrier-mediated ferromagnet. Here, we have used transmission electron microscopy and polarized neutron reflectometry to characterize the interface between GaMnAs-based layers designed to have anisotropy vectors oriented at right angles from one another. For a bilayer of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ and ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$, we find that the entirety of the ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ layer exhibits in-plane magnetic anisotropy and that the $majority$ of the ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ exhibits perpendicular anisotropy. However, near the ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ interface, we observe a thin Mn-rich region of the nominally perpendicular ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ that instead exhibits $in\ensuremath{-}plane$ anisotropy. Using first-principles energy considerations, we explain this sublayer as a natural consequence of interfacial carrier migration.

Recently, the design and realization of a sputter-deposition system for in situ and in operando polarized neutron reflectometry (PNR) was reported. The device allows magnetic thin films and heterostructures to be grown, while the sample remains aligned in the neutron beam for PNR. By now, it has been applied in experiments that investigated the magnetic and structural properties of thin Fe and Pd/Fe/Pd heterostructures as a function of the layer thickness. Here, we report on significant upgrades of the deposition system with advanced thin film growth and measurement capabilities. These include improvements to the generation of the vacuum to realize ultra-high-vacuum (UHV) conditions. A base pressure below 5 × 10−9mbar can now be obtained within less than one day of pumping time. To allow experiments over a wide range of temperatures, the system was upgraded to include a cryo-furnace. It allows the sample to be cooled or heated in the range of 10K to 1000K for both applications, sample growth and measurement. Further, a new magnetic coil setup with soft iron yoke was designed which can realize a homogeneous in-plane magnetic field of up to 300mT and electric fields at the sample position.

We report on the evolution of the average and depth-dependent magnetic order in thin-film samples of biaxially stressed and electron-doped EuTiO3 for samples across a doping range < 0.1 to 7.8 × 1020 cm-3. Under an applied in-plane magnetic field, the G-type antiferromagnetic ground state undergoes a continuous spin-flop phase transition into in-plane, field-polarized ferromagnetism. The critical field for ferromagnetism slightly decreases with an increasing number of free carriers, yet the field evolution of the spin-flop transition is qualitatively similar across the doping range. Unexpectedly, we observe interfacial ferromagnetism with saturated Eu2+ moments at the substrate interface at low fields preceding ferromagnetic saturation throughout the bulk of the degenerate semiconductor film. We discuss the implications of these findings for the unusual magnetotransport properties of this compound.