The Impact of Local Strain Fields in Noncollinear Antiferromagnetic Films.

Antiferromagnets hosting structural or magnetic order that breaks time reversal symmetry are of increasing interest for "beyond von Neumann" computing applications because the topology of their band structure allows for intrinsic physical properties, exploitable in integrated memory and logic function. One such group are the noncollinear antiferromagnets. Essential for domain manipulation is the existence of small net moments found routinely when the material is synthesized in thin film form and attributed to symmetry breaking caused by spin canting, either from the Dzyaloshinskii-Moriya interaction or from strain.

Optimizing Hot Electron Harvesting at Planar Metal-Semiconductor Interfaces with Titanium Oxynitride Thin Films.

Understanding metal-semiconductor interfaces is critical to the advancement of photocatalysis and sub-bandgap solar energy harvesting where electrons in the metal can be excited by sub-bandgap photons and extracted into the semiconductor. In this work, we compare the electron extraction efficiency across Au/TiO and titanium oxynitride (TiON)/TiO interfaces, where in the latter case the spontaneously forming oxide layer (TiO) creates a metal-semiconductor contact. Time-resolved pump-probe spectroscopy is used to study the electron recombination rates in both cases.

Assembly, structure and thermoelectric properties of 1,1'-dialkynylferrocene 'hinges'.

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.

Multi-component self-assembled molecular-electronic films: towards new high-performance thermoelectric systems.

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.

Optimised power harvesting by controlling the pressure applied to molecular junctions.

A major potential advantage of creating thermoelectric devices using self-assembled molecular layers is their mechanical flexibility. Previous reports have discussed the advantage of this flexibility from the perspective of facile skin attachment and the ability to avoid mechanical deformation. In this work, we demonstrate that the thermoelectric properties of such molecular devices can be controlled by taking advantage of their mechanical flexibility.

Spin-orbit coupling suppression and singlet-state blocking of spin-triplet Cooper pairs.

An inhomogeneous magnetic exchange field at a superconductor/ferromagnet interface converts spin-singlet Cooper pairs to a spin-polarized triplet state. Although the decay envelope of triplet pairs within ferromagnetic materials is well studied, little is known about their decay in nonmagnetic metals and superconductors and, in particular, in the presence of spin-orbit coupling (SOC). Here, we investigate devices in which singlet and triplet supercurrents propagate into the s-wave superconductor Nb.

Tuning the thermoelectrical properties of anthracene-based self-assembled monolayers.

It is known that the electrical conductance of single molecules can be controlled in a deterministic manner by chemically varying their anchor groups to external electrodes. Here, by employing synthetic methodologies to vary the terminal anchor groups around aromatic anthracene cores, and by forming self-assembled monolayers (SAMs) of the resulting molecules, we demonstrate that this method of control can be translated into cross-plane SAM-on-gold molecular films. The cross-plane conductance of SAMs formed from anthracene-based molecules with four different combinations of anchors are measured to differ by a factor of approximately 3 in agreement with theoretical predictions.

Scale-Up of Room-Temperature Constructive Quantum Interference from Single Molecules to Self-Assembled Molecular-Electronic Films.

The realization of self-assembled molecular-electronic films, whose room-temperature transport properties are controlled by quantum interference (QI), is an essential step in the scale-up of QI effects from single molecules to parallel arrays of molecules. Recently, the effect of QI (DQI) on the electrical conductance of self-assembled monolayers (SAMs) has been investigated. Here, through a combined experimental and theoretical investigation, we demonstrate chemical control of different forms of QI (CQI) in cross-plane transport through SAMs and assess its influence on cross-plane thermoelectricity in SAMs.

The electrochemical behaviour of magnetocaloric alloys La(Fe,Mn,Si)H under magnetic field conditions.

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.

Plasmon induced thermoelectric effect in graphene.

Graphene has emerged as a promising material for 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 conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile.

Cross-plane conductance through a graphene/molecular monolayer/Au sandwich.

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.

Hexapod Hall scanner for high-resolution large area magnetic imaging.

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.

Andreev reflection spectroscopy in transition metal oxides.

Here we review the literature concerning measurement of the Andreev reflection between a superconductor (S) and ferromagnet (F), with particular attention to the case where the ferromagnet is a transition metal oxide. We discuss the practicality of utilization of the current models for determination of the transport current spin polarization and examine the evidence for Andreev bound states.This article is part of the theme issue 'Andreev bound states'.

Giant Piezomagnetism in MnNiN.

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 MnNiN, facilitated by its geometrically frustrated antiferromagnetism opening the possibility of new memory device concepts. Films of MnNiN with intrinsic biaxial strains of ±0.

Enhanced spin pumping into superconductors provides evidence for superconducting pure spin currents.

Unlike conventional spin-singlet Cooper pairs, spin-triplet pairs can carry spin. 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 materials.

Realization of ground state in artificial kagome spin ice via topological defect-driven magnetic writing.

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.

Graphene gas sensing using a non-contact microwave method.

We report a non-contact CVD graphene gas sensing method that utilises a high Q microwave dielectric resonator perturbation technique. A graphene sample is coupled to the evanescent field of a dielectric resonator whereupon nitrogen dioxide (NO), a p-doping gas, is detected by monitoring the change in the linewidth and frequency of the resonant mode. The resonant peak shape is dependent on the number of carriers in the graphene sheet.

A novel method for the injection and manipulation of magnetic charge states in nanostructures.

Realising the promise of next-generation magnetic nanotechnologies is contingent on the development of novel methods for controlling magnetic states at the nanoscale. There is currently demand for simple and flexible techniques to access exotic magnetisation states without convoluted fabrication and application processes. 360° domain walls (metastable twists in magnetisation separating two domains with parallel magnetisation) are one such state, which is currently of great interest in data storage and magnonics.

Reduction Dynamics of Doped Ceria, Nickel Oxide, and Cermet Composites Probed Using In Situ Raman Spectroscopy.

The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface.

Low temperature and high field regimes of connected kagome artificial spin ice: the role of domain wall topology.

Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges.

Hexagonal Boron Nitride assisted transfer and encapsulation of large area CVD graphene.

We report a CVD hexagonal boron nitride (hBN-) assisted transfer method that enables a polymer-impurity free transfer process and subsequent top encapsulation of large-area CVD-grown graphene. We demonstrate that the CVD hBN layer that is utilized in this transfer technique acts as a buffer layer between the graphene film and supporting polymer layer. We show that the resulting graphene layers possess lower doping concentration, and improved carrier mobilities compared to graphene films produced by conventional transfer methods onto untreated SiO2/Si, SAM-modified and hBN covered SiO2/Si substrates.

Magnetic relaxation dynamics driven by the first-order character of magnetocaloric La(Fe,Mn,Si)13.

Here, we study the temporal evolution of the magnetic field-driven paramagnetic to ferromagnetic transition in the La(Fe,Mn,Si)13 material family. Three compositions are chosen that show varying strengths of the first-order character of the transition, as determined by the relative magnitude of their magnetic hysteresis and temperature separation between the zero-field transition temperature Tc and the temperature Tcrit, where the transition becomes continuous. Systematic variations in the fixed field, isothermal rate of relaxation are observed as a function of temperature and as a function of the degree of first-order character.

Plasmon-induced optical anisotropy in hybrid graphene-metal nanoparticle systems.

Hybrid plasmonic metal-graphene systems are emerging as a class of optical metamaterials that facilitate strong light-matter interactions and are of potential importance for hot carrier graphene-based light harvesting and active plasmonic applications. Here we use femtosecond pump-probe measurements to study the near-field interaction between graphene and plasmonic gold nanodisk resonators. By selectively probing the plasmon-induced hot carrier dynamics in samples with tailored graphene-gold interfaces, we show that plasmon-induced hot carrier generation in the graphene is dominated by direct photoexcitation with minimal contribution from charge transfer from the gold.