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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.

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.

The magnetocaloric effect has seen a resurgence in interest over the last 20 years as a means towards an alternative energy efficient cooling method. This has resulted in a concerted effort to develop the so-called “giant” magnetocaloric materials with large entropy changes that often come at the expense of hysteretic behavior. But do the gains offset the disadvantages? In this paper, we review the relationship between the latent heat of several giant magnetocaloric systems and the associated magnetic field hysteresis. We quantify this relationship by the parameter Δμ 0 H/ΔS L, which describes the linear relationship between field hysteresis, Δμ 0 H, and entropy change due to latent heat, ΔS L. The general trends observed in these systems suggest that itinerant magnets appear to consistently show large ΔS L accompanied by small Δμ 0 H (Δμ 0 H/ΔS L = 0.02 ± 0.01 T/(J K−1 kg−1)), compared to local moment systems, which show significantly larger Δμ 0 H as ΔS L increases (Δμ 0 H/ΔS L = 0.14 ± 0.06 T/(J K−1 kg−1)).

Free monopoles have fascinated and eluded researchers since their prediction by Dirac1 in 1931. In spin ice, the bulk frustrated magnet, local ordering principles known as ice rules—two-in/two-out for four spins arranged in a tetrahedron—minimize magnetic charge. Remarkably, recent work2, 3, 4, 5 shows that mobile excitations, termed ‘monopole defects’, emerge when the ice rules break down2. Using a cobalt honeycomb nanostructure we study the two-dimensional planar analogue called kagome or artificial spin ice. Here we show direct images of kagome monopole defects and the flow of magnetic charge using magnetic force microscopy. We find the local magnetic charge distribution at each vertex of the honeycomb pins the magnetic charge carriers, and opposite charges hop in opposite directions in an applied field. The parameters that enter the problem of creating and imaging monopole defects can be mapped onto a simple model that requires only the ice-rule violation energy and distribution of switching fields of the individual bars of a cobalt honeycomb lattice. As we demonstrate, it is the exquisite interplay between these energy scales in the cobalt nanostructure that leads to our experimental observations.

We report on investigation of the spin dynamics in InAs and InSb films grown on GaAs at a temperature range from 77 K to 290 K. For both materials, the large lattice mismatch with the GaAs substrate results in the formation of an interface accumulation layer with a large defect concentration, which strongly affects the spin relaxation in these areas. Moreover, the native surface defect in the InAs films resulted in an additional charge accumulation layer with high conductivity, but very short spin lifetime. In contrast, in InSb layers, the surface states introduce a depletion region. We have correlated the spin relaxation with a multi-layer analysis of the transport properties, and find that in a 1 μm thick InAs film, approximately 70% of the total current flows through the interface and surface accumulation layers, which have sub-picosecond lifetimes, whereas in InSb films of the same thickness, the semiconducting layer carries more than 90% of the total current, and the spin lifetime in the accumulation layer is only slightly less than that of the central semiconducting layer. We suggest that InSb could be a more attractive candidate for spintronic applications than InAs.

A complete characterization of high temperature superconducting films, as a function of microwave power, must track changes of the surface resistance and the penetration depth. A key problem has always been tracking power-dependent nonlinearities associated with a change in penetration depth. In this paper we report a technique that exploits the generic response of resonators to a microwave impulse. We show that a transient response is observed which has a frequency equal to the difference between the driving frequency and the resonant frequency of the resonator. Moreover, we demonstrate how this transient response can be used to determine the nonlinear properties of superconducting thin films.

A spray pyrolysis deposition technique has been used to prepare thick films of half-metallic ferromagnet La0.7Ca0.3MnO3 on LaAlO3 (001) and yttria-stabilized zirconia Y–ZrO2 (100) single-crystal substrates. The films deposited on LaAlO3 (001) exhibited a high degree of crystallinity with both in-plane and out-of-plane texture and a very sharp insulator to metal transition at TIM = 270 K. The intrinsic magnetoresistance (MR) reaches 70% at TIM in 3 T, a similar value as in the bulk material of the same composition. The extrinsic intergrain MR, however, is only 0.5% at 40 K in 3 T, 50 times smaller than for the bulk. By contrast, films grown on YSZ single crystals have a broad insulator to metal transition at a lower TIM of approximately 220 K and poor intrinsic MR. They show however an extrinsic MR as large as in the bulk. The extrinsic MR is interpreted as arising from crystalline and magnetic disorder at the grain boundaries.

A high temperature superconducting GdBa2Cu3O7−δ thin film was characterized using a parallel plate resonator at 5.5 GHz and a dielectric puck resonator at 10 GHz, to observe the dependence of surface resistance on microwave power at the fundamental frequency, and the production of intermodulation products using a two-tone measurement setup, respectively. The electromagnetic field pattern of the dielectric puck-HTS thin film mode was modeled using the commercial software package MAFIA. The intermodulation product was compared with a simple RSJ model.

A series of rhombohedral alkaline-earth-doped manganites, La1−x (Ca,Sr)x MnO3, were studied, with x = 0.28 to 0.375, a constant tolerance factor of 0.927 ± 0.002, a very small variation of the Mn–O bond angle (Tm, for x 4 0.28 was higher (by more than 20 K) than previously reported. With increasing x (and at the same time increasing Ca for Sr substitution), the Mn–O bond length shortened, Tm decreased, and the polaron hopping activation energy increased, indicative of increased carrier localization. The behavior is opposite to the La1−xSrxMnO3 series and can be explained by a strong dependence of the electron–phonon interaction on Mn–O bond length. In order to maximize Tm, Mn–O bond length must be controlled to a precise degree.

The nonlinear characteristics of YBCO (123) and TBCCO (2212) films were measured using the parallel plate resonator technique. The model approach has been developed as applied for this configuration. The current crowding at the edges of the rectangular structure is taken into consideration. A simple empirical model with few fitting parameters is used for a description of the surface impedance in linear and nonlinear mode. A suitable approximation has been found for the temperature dependence of the fitting parameter B0 corresponding to the threshold magnetic field for the onset of nonlinearity.

The structural changes and magnetoresistance (MR) properties of as-grown and post-annealed La0.7Ca0.3MnO3 films were investigated by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The data for the films were compared to that for bulk La0.7Ca0.3MnO3 post-annealed under the same conditions. The main structure of the as-grown films was face-centered pseudo-cubic with a doubled perovskite unit cell, of size ∼2ap × ∼2ap × 2ap, where ap is the single perovskite parameter. The phase showed a cube-on-cube epitaxy with the underlying LaAlO3 substrate. Upon annealing to a saturation point, a minor primitive pseudo-tetragonal structure evolved, of cell parameters . A total of four possible orientations of the two structures was observed by TEM, comprised of one orientation of the ∼ 2ap × ∼ 2ap × ∼ 2ap cell, i.e., the cube-on-cube epitaxy, giving rise to (00l) peaks in x-ray, and three orientations of the cell, giving rise to a single (00l)/(hk0) peak in x-ray. The bulk La0.7Ca0.3MnO3 sample also contains the × structure. The difference between the bulk and the film and the effects of annealing on films can be ascribed to the influence of strain between the film and substate, induced by lattice mismatch.

Using a 5-GHz parallel-plate resonator, several Gd 123 films and one Tl 2212 film have been studied as a function of microwave power. The variation of the surface resistance as a function of dc magnetic fields applied parallel to the crystallographicc axis reflects the gross microstructure of the films. Two broad categories of behavior are observed in dc field. The evidence for intrinsically limited power dependence is discussed in terms of impedance plane analysis.

Solid oxide fuel cells (SOFCs) have many advantages when compared to other fuel cell technologies, particularly for distributed stationary applications. As a consequence they are becoming ever more economically competitive with incumbent energy solutions. However, as with all technologies, improvements in durability, efficiency and cost is required before they become feasible alternatives. Such improvements are enabled through improved understanding of the critical material interactions occurring during operation. Raman spectroscopy is a noninvasive and non-destructive optical characterization tool which is ideally suited to the study of these critical chemical processes occurring within operational SOFCs. In this paper we will discuss advantages of using Raman characterization for understanding these important chemical processes occurring within SOFCs. We will present the specific examples of the type of measurement possible and discuss the direction of future research.

The recently discovered1 superconductor magnesium diboride, MgB2, has a transition temperature, Tc, approaching 40 K, placing it intermediate between the families of low- and high-temperature superconductors. In practical applications, superconductors are permeated by quantized vortices of magnetic flux. When a supercurrent flows, there is dissipation of energy unless these vortices are ‘pinned’ in some way, and so inhibited from moving under the influence of the Lorentz force. Such vortex motion ultimately determines the critical current density, Jc, which the superconductor can support. Vortex behaviour has proved to be more complicated in high-temperature superconductors than in low-temperature superconductors and, although this has stimulated extensive theoretical and experimental research2, it has also impeded applications. Here we describe the vortex behaviour in MgB2, as reflected in Jc and in the vortex creep rate, S, the latter being a measure of how fast the ‘persistent’ supercurrents decay. Our results show that naturally occurring grain boundaries are highly transparent to supercurrents, a desirable property which contrasts with the behaviour of the high-temperature superconductors. On the other hand, we observe a steep, practically deleterious decline in Jc with increasing magnetic field, which is likely to reflect the high degree of crystalline perfection in our samples, and hence a low vortex pinning energy.

A number of different compounds, such as those derived from LaMnO3, have recently been shown to exhibit very large changes (up to 106%) in electrical resistance when a magnetic field is applied1–4—a phenomenon known as colossal magnetoresistance (CMR). But magnetic fields of several tesla are typically required to obtain such a large magnetoresistive effect, thus limiting the potential for applications. Nevertheless the complex and intimate link between magnetic structure, crystallographic structure and electrical resistivity in CMR materials, in addition to being of fundamental scientific interest, appears to provide some scope for engineering a more sensitive magnetoresistive response. Here we elucidate the effect of specific structural defects on the CMR behaviour of the compound La0.7Ca0.3MnO3. We have made thin film devices that isolate the contribution of a single grain boundary that was introduced into an epitaxial film of the material by growing it on a bicrystal substrate. These devices display sharp resistance switching in magnetic fields orders of magnitude less than those normally associated with CMR. These results both provide insight into the role of grain boundaries, and demonstrate the potential for developing sub-micrometre magnetic field sensors based on the CMR effect.

Thin films of colossal magnetoresistance material La0.7Ca0.3MnO3 were implanted with different fluence 200keV Cr ions. Resistivity measurements in zero and applied fields of up to 8T were made in order to determine the effects of the implanted magnetic ions on the magnetoresistance (MR). As the Cr fluence was increased, the resistivity increased and the metal-insulator transition (MI) temperature was suppressed to values below the experimentally accessible temperature range as a result of oxygen loss and the creation of defects. However, for the highest fluence of 5×1015 ions/cm2, a re-entrant metal-insulator type transition was observed. Furthermore a significant improvement in the low field MR was observed for fields less than 500mT. These results are interpreted in terms of substitution of Cr ions onto Mn sites and the creation of a magnetically inhomogeneous material and the influence of oxygen deficiency.

Two 123 thin films grown by e-beam evaporation have been studied using Raman microscopy. The films were grown under different conditions of temperature and oxygen partial pressure and show different levels of cation disorder as determined from the ‘c’ axis lattice parameter in combination with x-ray data. The oxygen stoichiometry in each film was changed by controlled anneals using a coulometric titration apparatus. As a result we report on the sensitivity of the 500cm−1 and 585cm−1 Raman peak to the oxygen stoichiometry and how the intensity and position of these peaks can be used to detect or confirm the presence of a small amount of cation disorder.

We have examined the vortex dynamics in both as-grown and columnar-defected BSCCO 2212 crystals where the latter have been irradiated to produce columns alongs the crystallographic c-axis. Both the magnetisation and the (dynamic) relaxation rate have been measured as a function of field and temperature. Using a scaling analysis we extract the form of the energy scales of the characteristic critical current and pinning.

Magnetisation loops and (dynamic) relaxation rates of a variety of HTS single crystals have been measured with H‖c. In regions of H and T where magnetic hysteresis loops scale, the characteristic pinning energy and current have power law dependences on the B. We evaluate these exponents for the different crystals, and discuss their dependence on anisotropy and dimensionality of the dominant pinning mechanisms.