Abstract: The Nernst effect describes a linear relationship between orthogonal components of a magnetic field, a temperature gradient, and a resulting transverse electric field. A non-local electrical measurement, where injection and detection are physically separated on the specimen, serves as a versatile and effective platform for measuring spin and thermal effects due to the avoided interference with a charge current directly. Here, we quantify the Nernst coefficient of Pt, a common material for spin injection in non-local geometries, by a non-local electrical measurement under modulated temperature and magnetic field and finite element analysis for modeling heat transfer. We determine the Nernst coefficient of Pt from room temperature (8.56 nVK^-1 T^-1) to 10K (29.3 nVK^-1 T^-1). Beyond the quantification of the Nernst coefficient, our results show that careful consideration of the thermal properties of the thermal sink and electrode materials is needed when making an interpretation of non-local electrical measurements.

Full text available from Applied Physics Letters

Abstract: Entropy-stabilized oxides are single-phase, multicomponent oxides that are stabilized by a large entropy of mixing, ΔS, overcoming a positive enthalpy. Due to the −TΔS term in the Gibbs’ free energy, G, it can be hypothesized that entropy-stabilized oxides demonstrate a robust thermal stability. Here, we investigate the high temperature stability (1300–1700 °C) of the prototypical entropy-stabilized rocksalt oxide (MgCoNiCuZn)_0.2O in air. We find that at temperatures >1300 °C, the material gradually loses Cu and Zn with increasing temperature. Cu is lost through a selective melting as a Cu-rich liquid phase is formed. Zn is sublimed from the rocksalt phase at approximately similar temperatures to those corresponding to the Cu loss, significantly below both the melting temperature of ZnO and its solubility limit in a rocksalt phase. The elemental loss progressively reduces the entropy of mixing and results in a multiphase solid upon quenching to room temperature. We posit that the high-temperature solubility of Cu and Zn is correlated providing further evidence for entropic stabilization over general solubility arguments.

Full text available from Applied Physics Letters

Abstract: Non-collinear antiferromagnets are an exciting new platform for studying intrinsic spin Hall effects, phenomena that arise from the materials’ band structure, Berry phase curvature, and linear , 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. O ur work demonstrates symmetry control through the magnetic lattice as a pathway to tailored functionality in magnetoelectronic systems.

Full text available from Advanced Materials.

Abstract: Magnetoactive soft materials, typically composed of magnetic particles dispersed in a soft polymer matrix, are finding many applications in soft robotics due to their reversible and remote shape transformations under magnetic fields. To achieve complex shape transformations, anisotropic, and heterogeneous magnetization profiles must be programmed in the material. However, once programmed and assembled, magnetic soft actuators cannot be easily reconfigured, repurposed, or repaired, which limits their application, their durability, and versatility in their design. Here, magnetoactive soft composites are developed from squid-derived biopolymers and NdFeB microparticles with tunable ferromagnetic and thermomechanical properties. By leveraging reversible crosslinking nanostructures in the biopolymer matrix, a healing-assisted assembly process is developed that allows for on-demand reconfiguration and magnetic reprogramming of magnetoactive composites. This concept in multi-material modular actuators is demonstrated with programmable deformation modes, self-healing properties to recover their function after mechanical damage, and shape-memory behavior to lock in their preferred configuration and un-actuated catch states. These dynamic magnetic soft composites can enable the modular design and assembly of new types of magnetic actuators, not only eliminating device vulnerabilities through healing and repair but also by providing adaptive mechanisms to reconfigure their function on demand.

Full text available from Advanced Functional Materials.

Abstract: Functional thin film superlattices with stability in extreme environments can lead to transformative performance in optical and thermal applications such as thermophotovoltaics. In this work, key issues associated with defects that prevent layer-by-layer growth in epitaxial, low-miscibility oxide superlattices are investigated. Layer protrusions, approximately 8 nm wide and 3 nm thick, arise from a strain relaxation mechanism in 8 nm bilayer superlattices of Ba(Zr_0.5Hf_0.5)O₃/MgO and propagate through the subsequent superlattice layers forming an inverted pyramid structure that is spatially phase offset from the matrix. The density and size of these defects scales with the number of interfaces in the sample, indicating that surface roughness during growth is a significant factor in the formation of these defects. In situ high temperature transmission electron microscopy (1000 °C, in vacuo) measurement reveals that phase decomposition of Ba(Zr_0.5Hf_0.5)O₃ and decoherence of the superlattice is nucleated by these defects. This work highlights that achieving optimum growth conditions is imperative to the synthesis of single-crystalline superlattices with sharp interfaces for optimized performance in extreme environments.

Full text available from Journal of Applied Physics.