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The magnetically frustrated manganese nitride antiperovskite family displays significant changes of entropy under changes in hydrostatic pressure near a first-order antiferromagnetic to paramagnetic phase transition that can be useful for the emerging field of solid-state barocaloric cooling. In previous studies, the transition hysteresis has significantly reduced the reversible barocaloric effects (BCE). Here we show that the transition hysteresis can be tailored through quaternary alloying in the Mn3Cu 1 − x Sn x N system. We find the magnitude of hysteresis is minimised when Cu and Sn are equiatomic (x = 0.5) reaching values far less than previously found for Mn3 AN ( A = Pd, Ni, Ga, Zn), whilst retaining entropy changes of the same order of magnitude. These results demonstrate that reversible BCE are achievable for p 3(A, B)N family and suggest routes to modify the transition properties in compounds of the same family.

Ni-Mn-Ga based alloys are widely studied due to their potential for practical applications, making use of their martensitic transformations. However, hysteresis is a long-standing drawback that reduces the chance of transferring these alloys from the laboratory to industry. In this work, we studied a Cr-doped Ni2.15Mn0.70Cr0.15Ga alloy. We arrived at this composition by integrating data obtained from the previous phase and hysteresis diagrams taken from the literature. The compound presents a magnetostructural transition at room temperature, with a ferromagnetic martensite phase, and moderate thermal hysteresis of approximately 4 K. The magnetocaloric and ferromagnetic shape memory effects were explored, showing a reversible entropy change of approximately 9 Jkg-1K-1 under 0–5 T field change, and a cyclical magnetic-field-induced deformation close to 0.81% under 0–9 T, an advance towards high reversibility for this family alloys.

Sb2Te3 is a topological insulator (TI) material that can be used in a wide range of applications from energy harvesting to Spin-Orbitronics. In this paper, the structural, electrical, and thermal transport properties of nanocrystalline ion beam sputtered Sb2Te3 thin films were studied. Films with thicknesses between 35 and 300 nm, with nanocrystallites of sizes 10–20 nm, have a high resistivity between 0.072 and 2.03 Ω cm at 300 K, increasing with cooling. The Seebeck coefficient demonstrates the coexistence of n-type and p-type conduction, the latter being more prominent at high temperatures and in thicker films. The morphological and transport properties reveal that the films are constituted by two layers having different majority charge carriers, with the electronic bulk conduction being described by two semiconductor layers conducting in parallel, one p-type at the surface and another n-type, each described by an activation energy-dependent conductivity. Besides these bulk contributions, weak antilocalization (WAL) cusps are observed in the magnetoconductance below 10 K and at low magnetic fields. Analysis of the WAL hints that there is one two-dimensional conduction channel open at low temperatures for the thinner films, whereas for the thicker film, this 2D conduction appears to be masked by the bulk channels. However, a magnetic localization length LΦ between 62 and 90 nm at 2 K is observed for all thin films. This behavior suggests that as the bulk activation energy conductions freeze out at low temperatures, the electrical conduction is carried by the supposed 2D state, which appears to have some of the features of a TI surface state. Through these measurements, we demonstrate that the type of dominant conduction can be controlled by the Sb2Te3 film thickness in these large area sputtered films, while the conduction at low temperatures appears to be dominated by a robust TI state.

The magnetocaloric effect is often largest within the neighborhood of a first-order phase transition. This effect can be utilized in magnetocaloric refrigeration, which completely eliminates the need for the greenhouse gases utilized in conventional refrigeration. However, such transitions present unique dynamical effects and are accompanied by hysteresis, which can be detrimental for such refrigeration applications. In this work, a Landau theory-based relaxational model is used to study the magnetic hysteresis and dynamics of the first-order magnetic transition of LaFe13−x Si x . Fitting the experimental magnetization data as a function of applied magnetic field under different field sweep rates with this model provided the Landau parameters (A, B, and C) and the kinetic coefficient of the studied material. We demonstrate the tendency of the magnetic hysteresis to increase with the magnetic field sweep rate, underlining the importance of studying and minimizing the magnetic hysteresis in magnetic refrigerants at practical field sweep rates. While evaluating the temperature dependence of the time required for a complete transition to occur, a nonmonotonic behavior and a sharp peak were found for temperatures near the transition temperature. Such peaks occur at the same temperature as the peak of the magnetic entropy change for low fields, whereas for higher fields the two peaks decouple. This information is critical for technological applications (such as refrigerators/heat pumps) as it provides guidelines for the optimization of the magnetic field amplitude in order to reduce the transition timescale and consequently maximize the machine operational frequency and amount of heat that is pumped in/out per second.

The thermoelectric properties of parallel arrays of organic molecules on a surface offer the potential for large-area, flexible, solution processed, energy harvesting thin-films, whose room-temperature transport properties are controlled by quantum interference (QI). Recently, it has been demonstrated that constructive QI (CQI) can be translated from single molecules to self-assembled monolayers (SAMs), boosting both electrical conductivities and Seebeck coefficients. However, these CQI-enhanced systems are limited by rigid coupling of the component molecules to metallic electrodes, preventing the introduction of additional layers which would be advantageous for their further development. These rigid couplings also limit our ability to suppress the transport of phonons through these systems, which could act to boost their thermoelectric output, without comprising on their impressive electronic features. Here, through a combined experimental and theoretical study, we show that cross-plane thermoelectricity in SAMs can be enhanced by incorporating extra molecular layers. We utilize a bottom-up approach to assemble multi-component thin-films that combine a rigid, highly conductive ‘sticky’-linker, formed from alkynyl-functionalised anthracenes, and a ‘slippery’-linker consisting of a functionalized metalloporphyrin. Starting from an anthracene-based SAM, we demonstrate that subsequent addition of either a porphyrin layer or a graphene layer increases the Seebeck coefficient, and addition of both porphyrin and graphene leads to a further boost in their Seebeck coefficients. This demonstration of Seebeck-enhanced multi-component SAMs is the first of its kind and presents a new strategy towards the design of thin-film thermoelectric materials.

Hot carrier based methods constitute a valuable approach for efficient and silicon compatible sub-bandgap photodetection. Although, hot electron excitation and transfer have been studied extensively on traditional materials such as Au and Ti, reports on alternative materials such as titanium nitride (TiN) are rare. Here, we perform hot hole photodetection measurements on a p-Si/metal thin film junction using Ti, Au and TiN. This material is of interest as it constitutes a refractory alternative to Au which is an important property for plasmonic applications where high field intensities can occur. In contrast to Au, a TiN/Si junction does not suffer from metal diffusion into the Si, which eases the integration with current Si-fabrication techniques. This work shows that a backside illuminated p-Si/TiN system can be used for efficient hot hole extraction in the IR, allowing for a responsivity of 1 mA/W at an excitation wavelength of 1250 nm and at zero bias. Via a comparison between TiN and other commonly used materials such as Au, the origin of this comparably high photoresponse can be traced back to be directly linked to a thin TiO2-x interfacial layer allowing for a distinct hot-hole transfer mechanism. Moreover, the fabrication of TiN nanodisk arrays is demonstrated which bears great promise to further boost the device efficiency.

This work demonstrates precision control of hydrogen content in La(Fe,Co,Si)13Hδ for the development of environmentally friendly magnetocaloric-based cooling technologies, using an electrolytic hydriding technique. We show the Curie temperature, a critical parameter which directly governs the temperature window of effective cooling, can be varied easily and reproducibly in 1 K steps within the range 274 K to 402 K. Importantly, both partially (up to 10%) and fully hydrided compositions retain favorable entropy change values comparable to that of the base composition. Crucially, we show in these second-order phase transition compounds, partial hydriding is stable and not susceptible against phase separation.

Dialkynylferrocenes exhibit attractive electronic and rotational features that make them ideal candidates for use in molecular electronic applications. However previous works have primarily focussed on single-molecule studies, with limited opportunities to translate these features into devices. In this report, we utilise a variety of techniques to examine both the geometric and electronic structure of a range of 1,1'-dialkynylferrocene molecules, as either single-molecules, or as self-assembled monolayers. Previous single molecule studies have shown that similar molecules can adopt an 'open' conformation. However, in this work, DFT calculations, STM-BJ experiments and AFM imaging reveal that these molecules prefer to occupy a 'hairpin' conformation, where both alkynes point towards the metal surface. Interestingly we find that only one of the terminal anchor groups binds to the surface, though both the presence and nature of the second alkyne affect the thermoelectric properties of these systems. First, the secondary alkyne acts to affect the position of the frontier molecular orbitals, leading to increases in the Seebeck coefficient. Secondly, theoretical calculations suggested that rotating the secondary alkyne away from the surface acts to modulate thermoelectric properties. This work represents the first of its kind to examine the assembly of dialkynylferrocenes, providing valuable information about both their structure and electronic properties, as well as unveiling new ways in which both of these properties can be controlled.

The magnetically frustrated manganese nitride antiperovskite family displays significant changes of entropy under hydrostatic pressure that can be useful for the emerging field of barocaloric cooling. Here we show that barocaloric properties of metallic antiperovskite Mn nitrides can be tailored for room-temperature application through quaternary alloying. We find an enhanced entropy change of $|\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{t}}|=37\phantom{\rule{4pt}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}$ at the ${T}_{t}=300\phantom{\rule{4pt}{0ex}}\mathrm{K}$ antiferromagnetic transition of quaternary ${\mathrm{Mn}}_{3}{\mathrm{Zn}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{N}$ relative to the ternary end members. The pressure-driven barocaloric entropy change of ${\mathrm{Mn}}_{3}{\mathrm{Zn}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{N}$ reaches $|\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{BCE}}|=20\phantom{\rule{4pt}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}$ in 2.9 kbar. Our results open up a large phase space where compounds with improved barocaloric properties may be found.

The degradation mechanism of La(Fe,Mn,Si)13Hx has been examined under conditions representative of the complex operating parameters of a refrigeration cycle. The magnetic field effects are found to be dominated by magneto-transport and are most significant when the material is in its paramagnetic state - resulting in significantly accelerated corrosion rates.

An inhomogeneous magnetic exchange field at a superconductor/ferromagnet interface converts spin-singlet Cooper pairs to a spin-aligned (i.e. spin-polarized) triplet state. Although the decay envelope of such triplet pairs within ferromagnetic materials is well studied, little is known about their decay in non-magnetic metals and superconductors, and in particular in the presence of spin-orbit coupling (SOC). Here we investigate devices in which triplet supercurrents are injected into the s-wave superconductor Nb. In the normal state of Nb, triplet supercurrents decay over a distance of 5 nm, which is an order of magnitude smaller than the decay of spin singlet pairs due to the SOC interacting with the spin associated with triplet pairs. In the superconducting state of Nb, triplet supercurrents are not able to couple with the singlet wavefunction and thus blocked by the absence of available equilibrium states in the singlet gap. The results offer new insight into the dynamics between s-wave singlet and s-wave triplet states., 19 pages, 5 figures

Thermal hysteresis is recognized as one of the main drawbacks for cyclical applications of magnetocaloric and ferromagnetic shape memory materials with first order transformations. As such, the challenge is to develop strategies that improve the compatibility between the phases involved in the transitions and study its influence on thermal hysteresis. With this purpose, we explore the thermal, structural and magnetic properties of the Ni2Mn1-xCuxGa0.84Al0.16 Heusler alloys. The alloys present a thermal hysteresis reduction of ~60% when the Cu content in the compound varies from x = 0.10 to x = 0.25, with a minimum hysteresis width of 6 K being achieved. We applied the geometric non-linear theory of martensite to address the phase compatibility, quantified by the parameter lambda2, the middle eigenvalue of the transformation stretch tensor, and found that the minimum of hysteresis is associated with a better crystallographic compatibility (lambda2 closer to 1) between the austenite and martensite phases. In addition, we show that the valley-like properties of hysteresis found in the Ni2Mn1-xCuxGa0.84Al0.16 compounds is present in several other alloys in the literature. These results provide new pathways to understand as well as to masters the phase compatibility and ultimately achieve a low thermal hysteresis in multifunctional Heusler alloys., 29 pages and 8 figures

This Conference Presentation, "Oxide-enhanced IR hot-carrier-based photo detection in metal thin-film Si junctions" was recorded at Photonics West 2020 held in San Francisco, California, United States.

Ferromagnetic Ni2MnGa-based alloys play an important role in technological fields, such as smart actuators, magnetic refrigeration and robotics. The possibility of obtaining large non-contact deformation induced by an external perturbation is one of its key strengths for applications. However, the search for materials with low cost, practical fabrication procedures and large signal output under small perturbing fields still poses challenges. In the present study we demonstrate that by judicial choice of substitution on the Mn site, an abrupt magnetostructural transition from a paramagnetic austenite phase to a ferromagnetic martensite one can be tuned to close to room temperature achieving large and reproducible strains. The required magnetic field to induce the strain varies from small values, as low as 0.25 T for 297.4 K and 1.6% of strain, to 8 T for 305 K and 2.6% of strain. Our findings point to encouraging possibilities for application of shape memory alloys in relatively inexpensive, scalable polycrystalline materials., Comment: 26 pages and 7 figures

Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.

In recent years infiltration of materials into porous ceramic scaffolds has been shown to be an effective way of creating catalytically active components for solid oxide fuel cells (SOFCs). However, the redox properties of these novel structures are not well understood. Here, we use X‐ray photoelectron spectroscopy (XPS) and in‐situ Raman spectroscopy to investigate the oxidation properties of yttria‐stabilised zirconia (YSZ) scaffolds infiltrated with ceria (CeO2), gadolinium‐doped ceria (GDC) and zirconia‐doped ceria (ZDC), with and without Ni. XPS shows that doping ceria with zirconia increases the ratio of Ce3+ to Ce4+, while gadolinium doping results in a decrease of Ce3+. The presence of Ni increases the Ce3+/Ce4+ ratio for CeO2 and GDC, but had little effect on ZDC. We used the shift of the F2g Raman peak to monitor in‐situ, the oxidation state of ceria. In the as‐made compounds, we show that while the gadolinium and zirconium dopants significantly change the oxidation characteristics of ceria, the resulting materials are only significantly reduced above 500 °C when co‐infiltrated with Ni. In‐situ Raman monitoring during reduction as a function of temperature showed that while ZDC reduces much more readily than undoped ceria or GDC, the presence of Ni dominated the reduction dynamics.

Refractory transition metal nitrides and oxynitrides are of interest for plasmonic applications due to their increased thermal stability, tunability and comparatively low loss. Presented here is an experimental investigation of reactively sputtered niobium oxynitride thin films, demonstrating screened plasma wavelengths tunable over a ~90 nm spectral range. The optical response is correlated with resistivity and Hall measurements. Additionally, an explanation is provided for the double epsilon-near-zero (2ENZ) behavior observed and it is compared with other material systems. Experimental analysis of film composition and structure are combined with computational modelling, based on density functional theory, to explain the dispersion behavior observed and indicate that 2ENZ behavior arises due to the incorporation of oxygen within the films during deposition.

The anomalous Hall effect (AHE) has been shown to be present in certain non-collinear antiferromagnets due to their symmetry-breaking magnetic structure, and its magnitude is dependent primarily on the non-zero components of the Berry curvature. In the non-collinear antiferromagnet Mn3NiN, the Berry phase contribution has been predicted to have strong strain dependence, although in practice, direct observation may be obscured by other strain-related influences—for instance, magnetic phase transitions mediated by strain. To unravel the various contributions, we examine the thickness and temperature dependence of the AHE for films grown on the piezoelectric substrate BaTiO3. We observe a systematic reduction in TN due to increased compressive strain as film thickness is reduced and a linear decrease in the AHE magnitude as the films are cooled from their ferrimagnetic phase above TN to their antiferromagnetic phase below. At 190 K, we applied an electric field across a 0.5 mm thick BaTiO3 substrate with a 50 nm thick Mn3NiN film grown on top and we demonstrate that at the coercive field of the piezoelectric substrate, the tensile in-plane strain is estimated to be of the order of 0.15%, producing a 20% change in AHE. Furthermore, we show that this change is, indeed, dominated by the intrinsic strain dependence of the Berry curvature.

Arrays of non-interacting nanomagnets are widespread in data storage and processing. As current technologies approach fundamental limits on size and thermal stability, enhancing functionality through embracing the strong interactions present at high array densities becomes attractive. In this respect, artificial spin ices are geometrically frustrated magnetic metamaterials that offer vast untapped potential due to their unique microstate landscapes, with intriguing prospects in applications from reconfigurable logic to magnonic devices or hardware neural networks. However, progress in such systems is impeded by the inability to access more than a fraction of the total microstate space. Here, we demonstrate that topological defect-driven magnetic writing—a scanning probe technique—provides access to all of the possible microstates in artificial spin ices and related arrays of nanomagnets. We create previously elusive configurations such as the spin-crystal ground state of artificial kagome dipolar spin ices and high-energy, low-entropy ‘monopole-chain’ states that exhibit negative effective temperatures. Elusive magnetic configurations of geometrically frustrated artificial kagome dipolar spin ices are realized by means of topological defect-driven magnetic writing.

Magnetic solid state cooling applications require families of samples where the magnetic transition is cascaded across the working range of the fridge. Although magnetic properties are widely studied, information relating to the mechanical properties of such systems is less prevalent. Here we study the mechanical properties of a series of magnetocaloric La(Co,Fe,Si)13 samples where the Co content is varied to produce a range of transition temperatures. It was found that at room temperature the flexural strength decreases and the Young's modulus increases with increasing Co content. Interestingly we find a significant reduction of Young's modulus at temperature around the magnetic transition temperature. This reduction was less pronounced with increasing Co content. We associate the softening with the magnetovolume coupling known to exist in these materials.

Ferromagnetic resonance (FMR) is performed on kagome artificial spin ice (ASI) formed of disconnected ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ nanowires. Here we break the threefold angular symmetry of the kagome lattice by altering the coercive field of each sublattice via shape anisotropy modification. This allows for distinct high-frequency responses when a magnetic field is aligned along each sublattice and additionally enables simultaneous spin-wave resonances to be excited in all nanowire sublattices, unachievable in conventional kagome ASI. The different coercive field of each sublattice allows selective magnetic switching via global field, unlocking novel microstates inaccessible in homogeneous-nanowire ASI. The distinct spin-wave spectra of these states are detected experimentally via FMR and linked to underlying microstates using micromagnetic simulation.

We report Abrikosov vortex nucleation in $\mathrm{Pt}/\mathrm{Nb}/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Nb}/\mathrm{Pt}$ proximity-coupled structures under oblique ferromagnetic resonance that turns out to be detrimental to superconducting spin pumping. By measuring an out-of-plane field-angle ${\ensuremath{\theta}}_{H}$ dependence and comparing with Pt-absent control samples, we show that as ${\ensuremath{\theta}}_{H}$ increases, the degree of enhancement (suppression) of spin pumping efficiency in the superconducting state for the Pt-present (Pt-absent) sample diminishes and it reverts to the normal state value at ${\ensuremath{\theta}}_{H}={90}^{\ensuremath{\circ}}$. This can be explained in terms of a substantial out-of-plane component of the resonance field for the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ layer (with in-plane magnetization anisotropy and high aspect ratio) that approaches the upper critical field of the Nb, turning a large fraction of the singlet superconductor volume into the normal state.

We investigate titanium nitride (TiN) thin film coatings on silicon for CMOS-compatible sub-bandgap charge separation upon incident illumination, which is a key feature in the vast field of on-chip photodetection and related integrated photonic devices. Titanium nitride of tunable oxidation distributions serves as an adjustable broadband light absorber with high mechanical robustness and strong chemical resistivity. Backside-illuminated TiN on p-type Si (pSi) constitutes a self-powered and refractory alternative for photodetection, providing a photoresponsivity of about ∼1 mA/W at 1250 nm and zero bias while outperforming conventional metal coatings such as gold (Au). Our study discloses that the enhanced photoresponse of TiN/pSi in the near-infrared spectral range is directly linked to trap states in an ultrathin TiO2–x interfacial interlayer that forms between TiN and Si. We show that a pSi substrate in conjunction with a few nanometer thick amorphous TiO2–x film can serve as a platform for photocurrent enhancement of various other metals such as Au and Ti. Moreover, the photoresponse of Au on a TiO2–x/pSi platform can be increased to about 4 mA/W under 0.45 V reverse bias at 1250 nm, allowing for controlled photoswitching. A clear deviation from the typically assumed Fowler-like response is observed, and an alternative mechanism is proposed to account for the metal/semiconductor TiO2–x interlayer, capable of facilitating hole transport.

Graphene has emerged as a promising material for photonics and optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a built-in field driven photovoltaic effect and a more dominant hot- carrier-assisted photothermoelectric (PTE) effect. The hot-carrier PTE effect is understood to rely on abrupt variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we report on the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At a certain gate bias, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for the development of hot carrier based plasmonic devices.

Ferromagnetic Josephson junctions (FJJs), comprised of two superconductors separated by a ferromagnet, have been developed extensively because of their unconventional physical properties and potential applications in superconducting spintronics. Nevertheless, the dynamical properties of FJJs have not been sufficiently investigated. The authors' experiments show that for thick FJJs, the magnetization dynamics of the middle layer are significantly modified by Meissner screening and magnetic flux pinning in the thick outer layers. Proper selection of the superconducting material provides dynamic access to the spin-polarized supercurrents in FJJs for high-frequency device applications.

A series of high quality BaFe$_{2-x}$Ni$_x$As$_2$ pnictide superconductors were studied using magnetic relaxation and isothermal magnetic measurements in order to study the second magnetization peak (SMP) and critical current behaviour in Ni-doped 122 family. The temperature dependence of the magnetic relaxation rate suggests a pinning crossover, whereas, it's magnetic field dependence hints a vortex-lattice structural phase-transition. The activation energy ($U$) estimated using the magnetic relaxation data was analyzed in detail for slightly-underdoped, slightly-overdoped and an overdoped samples, using Maley's method and collective creep theory. Our results confirm that the SMP in these samples is due to the collective (elastic) to plastic creep crossover as has been observed for the other members of 122-family. In addition, we also investigated the doping dependence of the critical current density ($J_c$) and the vortex-pinning behaviour in these compounds. The observed $J_c$ is higher than the threshold limit (10$^5$ A/cm$^2$) considered for the technological potential and even greater than 1 MA/cm$^2$ for slightly underdoped Ni-content, x = 0.092 sample. The pinning characteristics were analyzed in terms of the models developed by Dew-Hughes and Griessen $et$ $al$, which suggest the dominant role of $\delta l$-type pinning., Comment: 26 pages, 13 figures, Accepted for publication in ACS Applied Electronic Materials 2019

Using localized surface plasmon resonances (LSPR) to focus electromagnetic radiation to the nanoscale shows the promise of unprecedented capabilities in optoelectronic devices, medical treatments and nanoscale chemistry, due to a strong enhancement of light-matter interactions. As we continue to explore novel applications, we require a systematic quantitative method to compare suitability across different geometries and a growing library of materials. In this work, we propose application-specific figures of merit constructed from fundamental electronic and optical properties of each material. We compare 17 materials from four material classes (noble metals, refractory metals, transition metal nitrides, and conductive oxides) considering eight topical LSPR applications. Our figures of merit go beyond purely electromagnetic effects and account for the materials’ thermal properties, interactions with adjacent materials, and realistic illumination conditions. For each application we compare, for simplicity, an optimized spherical antenna geometry and benchmark our proposed choice against the state-of-the-art from the literature. Our propositions suggest the most suitable plasmonic materials for key technology applications and can act as a starting point for those working directly on the design, fabrication, and testing of such devices.

We have studied the anomalous Hall effect (AHE) in strained thin films of the frustrated antiferromagnet Mn$_{3}$NiN. The AHE does not follow the conventional relationships with magnetization or longitudinal conductivity and is enhanced relative to that expected from the magnetization in the antiferromagnetic state below $T_{\mathrm{N}} = 260$\,K. This enhancement is consistent with origins from the non-collinear antiferromagnetic structure, as the latter is closely related to that found in Mn$_{3}$Ir and Mn$_{3}$Pt where a large AHE is induced by the Berry curvature. As the Berry phase induced AHE should scale with spin-orbit coupling, yet larger AHE may be found in other members of the chemically flexible Mn$_{3}A$N structure.

A recent ferromagnetic resonance study [Jeon et al., Nat. Mater. 17, 499 (2018)] has reported that spin pumping into a singlet superconductor (Nb) can be greatly enhanced over the normal state when the Nb is coupled to a large spin-orbit-coupling (SOC) spin sink such as Pt. This behavior has been explained in terms of the generation of spin-polarized triplet supercurrents via SOC at the Nb/Pt interface, acting in conjunction with a nonlocally induced magnetic exchange field. Here we report the effect of adding a ferromagnet (Fe) to act as an internal source of an additional exchange field to the adjacent Pt spin sink. This dramatically enhances the spin pumping efficiency in the superconducting state compared with either Pt and Fe separately, demonstrating the critical role of the exchange field in generating superconducting spin currents in the Nb.

We present measurements of ferromagnetic resonance driven spin pumping and inverse spin Hall effect in $\mathrm{NbN}/{\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$ (YIG) bilayers. A clear enhancement of the (effective) Gilbert damping constant of the thin-film YIG was observed due to the presence of the NbN spin sink. By varying the NbN thickness and employing spin-diffusion theory, we have estimated the room-temperature values of the spin-diffusion length and the spin Hall angle in NbN to be 14 nm and $\ensuremath{-}1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$, respectively. Furthermore, we have determined the spin mixing conductance of the NbN/YIG interface to be $10\phantom{\rule{0.16em}{0ex}}\mathrm{n}{\mathrm{m}}^{\ensuremath{-}2}$. The experimental quantification of these spin transport parameters is an important step towards the development of superconducting spintronic devices involving NbN thin films.

We analyze coexistence of antiferromagnetic and ferromagnetic phases in bulk iron-rhodium and its alloys with palladium, Fe50,4Rh49,6, Fe49,7Rh47,4Pd2,9 and Fe48,3Rh46,8Pd4,9, using neutron diffraction, magnetization and scanning Hall probe imaging. Temperature dependencies of the lattice parameters, AFM and FM phase weight fractions, and Fe magnetic moment values were obtained on cooling and heating across the AFM-FM transition. Substantial thermomagnetic hysteresis for the phases’ weight fractions and a relatively narrow one for the unit cell volume has been observed on cooling-heating. A clear dependence of hysteretic behavior on Pd concentration has been traced. Additional direct magnetic measurements of the spatial distribution of the phase transition are acquired using scanning Hall probe microscopy, which reveals the length scale of the phase coexistence and the spatial progression of the transition in the presence of external magnetic field. Also, the magnetic phase diagram has been constructed for a series of Pd-doped FeRh alloys. © 2020 Elsevier B.V. EL acknowledges funding from the UK EPSRC. LFC acknowledges funding from the EPSRC and InnovateUK: Project number: 105541. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. This work was partly supported by the state assignment of the Ministry of Science and Higher Education (themes “Flux” No. AAAA-A18-118020190112-8 and “Alloys” № AAAA-A19-119070890020-3).

The functionalities offered by single-molecule electrical junctions are yet to be translated into monolayer or few-layer molecular films, where making effective and reproducible electrical contact is one of the challenging bottlenecks. Here we take a significant step in this direction by demonstrating that excellent electrical contact can be made with a monolayer biphenyl-4,4'-dithiol (BPDT) molecular film, sandwiched between gold and graphene electrodes. This sandwich device structure is advantageous, because the current flows through the molecules to the gold substrate in a 'cross-plane' manner, perpendicular to the plane of graphene, yielding high-conductance devices. We elucidate the nature of the cross-plane graphene/molecule/Au transport using quantum transport calculations and introduce a simple analytical model, which captures generic features of the current-voltage characteristic. Asymmetry in junction properties results from the disparity in electrode electrical properties, the alignment of the BPDT HOMO-LUMO energy levels and the specific characteristics of the graphene electrode. The experimental observation of scalability of junction properties within the junction area, in combination with a theoretical description of the transmission probability of the thiol-graphene contact, demonstrates that between 10% and 100% of the molecules make contact with the electrodes, which is several orders of magnitude greater than that achieved to date in the literature.

Materials such as W, TiN, and SrRuO3 (SRO) have been suggested as promising alternatives to Au and Ag in plasmonic applications owing to their stability at high operational temperatures. However, investigation of the reproducibility of the optical properties after thermal cycling between room and elevated temperatures is so far lacking. Here, thin films of W, Mo, Ti, TiN, TiON, Ag, Au, SrRuO3 and SrNbO3 are investigated to assess their viability for robust refractory plasmonic applications. These results are further compared to the performance of SrMoO3 reported in literature. Films ranging in thickness from 50 to 105 nm are deposited on MgO, SrTiO3 and Si substrates by e-beam evaporation, RF magnetron sputtering and pulsed laser deposition, prior to characterisation by means of AFM, XRD, spectroscopic ellipsometry, and DC resistivity. Measurements are conducted before and after annealing in air at temperatures ranging from 300 to 1000° C for one hour, to establish the maximum cycling temperature and potential longevity at elevated temperatures for each material. It is found that SrRuO3 retains metallic behaviour after annealing at 800° C, while SrNbO3 undergoes a phase transition resulting in a loss of metallic behaviour after annealing at 400° C. Importantly, the optical properties of TiN and TiON are degraded as a result of oxidation and show a loss of metallic behaviour after annealing at 500° C, while the same is not observed in Au until annealing at 600° C. Nevertheless, both TiN and TiON may be better suited than Au or SRO for high temperature applications operating under vacuum conditions.

We quantify the spin Hall angle θ SH and spin-diffusion length l sd of Nb from inverse spin Hall effect (ISHE) measurements in Nb / Ni 80 Fe 20 bilayers under ferromagnetic resonance. By varying the Nb thickness t Nb and comparing to a Ni 80 Fe 20 / Pt reference sample, room temperature values of θ SH and l sd for Nb are estimated to be approximately −0.001 and 30 nm, respectively. We also investigate the ISHE as a function of temperature T for different t Nb . Above the superconducting transition temperature T c of Nb , a clear t Nb -dependent T evolution of the ISHE is observed whereas below T c , the ISHE voltage drops rapidly and is below the sensitivity of our measurement setup at a lower T. This suggests the strong decay of the quasiparticle (QP) charge-imbalance relaxation length across T c , as supported by an additional investigation of the ISHE in a different sample geometry along with model calculation. Our finding suggests careful consideration should be made when developing superconductor spin Hall devices that intend to utilize QP-mediated spin-to-charge interconversion.

We demonstrate a six-axis scanning imaging apparatus using piezo bending actuators with a large scan range. The six axes of motion of the bending actuators together with the coupling mechanism to the translation stage allow complete control of the sensor position and orientation over the scanning surface, which is ideal for the use of planar sensors such as Hall devices. In particular, the design allows for in situ correction of the probe tilt angle so that the sensor distance to sample surface can be minimized. We investigate the impact of this alignment on the quality of the measured data using an InSb Hall sensor and a magnetic sample. We also demonstrate a synchronous commutation setup that can greatly enhance the magnetic image by reducing the Hall signal offset.

Controlling magnetism with electric field directly or through strain-driven piezoelectric coupling remains a key goal of spintronics. Here, we demonstrate that giant piezomagnetism, a linear magneto-mechanic coupling effect, is manifest in antiperovskite Mn

Controlling magnetism with electric field directly or through strain-driven piezoelectric coupling remains a key goal of spintronics. Here, we demonstrate that giant piezomagnetism, a linear magneto-mechanic coupling effect, is manifest in antiperovskite Mn3NiN, facilitated by its geometrically frustrated antiferromagnetism opening the possibility of new memory device concepts. Films of Mn3NiN with intrinsic biaxial strains of ±0.25% result in Néel transition shifts up to 60 K and magnetization changes consistent with theory. Films grown on BaTiO3 display a striking magnetization jump in response to uniaxial strain from the intrinsic BaTiO3 structural transition, with an inferred 44% strain coupling efficiency and a magnetoelectric coefficient α (where α = dB/dE) of 0.018 G cm/V. The latter agrees with the 1000-fold increase over Cr2O3 predicted by theory. Overall, our observations pave the way for further research into the broader family of Mn-based antiperovskites where yet larger piezomagnetic effects are predicted to occur at room temperature.

We use a contactless microwave dielectric resonator gas sensing platform to study the adsorption dynamics of NO2 gas present in air onto a graphene surface. The use of microwaves removes the need for metal contacts that would otherwise be necessary for traditional conductivity measurements, and therefore allows non-invasive determination of NO2 concentrations to sub parts per million. As a result, gas-metal interactions and localised graphene doping in the vicinity of metal contacts are eliminated, with the advantage that only graphene-gas adsorbate interactions are responsible for the measured signal. We show that the sensor response for all considered concentrations can be described using a surface coverage dependent Langmuir model. We demonstrate that the possible variation of the NO2 binding energy, which is frequently considered as the main parameter, plays only a secondary role compared to the rising adsorption energy barrier with increasing NO2 coverage. The continuous distribution of the properties of the graphene adsorption sites used in the theoretical model is supported by our Kelvin probe and Raman surface analysis. Our results demonstrate that the non-invasive microwave method is a promising alternative platform for gas sensing. Moreover it provides valuable insights towards the understanding of the microscopic processes occurring in graphene based gas sensors, which is a key factor in the realization of reproducible and optimized device properties.

Unlike conventional spin-singlet Cooper pairs, spin-triplet pairs can carry spin1,2. Triplet supercurrents were discovered in Josephson junctions with metallic ferromagnet spacers, where spin transport can occur only within the ferromagnet and in conjunction with a charge current. Ferromagnetic resonance injects a pure spin current from a precessing ferromagnet into adjacent non-magnetic materials3,4. For spin-singlet pairing, the ferromagnetic resonance spin pumping efficiency decreases below the critical temperature (Tc) of a coupled superconductor5,6. Here we present ferromagnetic resonance experiments in which spin sink layers with strong spin-orbit coupling are added to the superconductor. Our results show that the induced spin currents, rather than being suppressed, are substantially larger in the superconducting state compared with the normal state; although further work is required to establish the details of the spin transport process, we show that this cannot be mediated by quasiparticles and is most likely a triplet pure spin supercurrent.

Extracting plasmon-induced hot carriers over a metal-semiconductor Schottky barrier enables photodetection below the semiconductor bandgap energy. However, interfacial carrier recombination hinders the efficiency and stability of this process, severely limiting its implementation in telecommunication. This study proposes and demonstrates the use of epitaxially grown lattice-matched SrTiO3 for interfacial passivation of silicon-based plasmonic Schottky devices. The devices are activated by an electrical soft-breakdown of the interfacial SrTiO3 layer, resulting in reproducible rectified Schottky characteristics. The transition to a low resistance state of the SrTiO3 layer boosts the extraction efficiency of hot holes upon resonant plasmonic excitation, giving rise to a two orders of magnitude higher photocurrent compared to devices with a native oxide layer. Photoresponse, tunability, and barrier height studies under reverse biases as high as 100 V present superior stability with the incorporation of the SrTiO3 layer. The investigation paves the way toward plasmon-induced photodetection for practical applications including those under challenging operating conditions.