Electrocaloric effects have been experimentally studied in ferroelectrics and incipient ferroelectrics, but not incipient ferroelectrics driven ferroelectric using strain. Here we use optimally oriented interdigitated surface electrodes to investigate extrinsic electrocaloric effects in low-loss epitaxial SrTiO 3 films near the broad second-order 243 K ferroelectric phase transition created by biaxial in-plane coherent tensile strain from DyScO 3 substrates. Our extrinsic electrocaloric effects are an order of magnitude larger than the corresponding effects in bulk SrTiO 3 over a wide range of temperatures including room temperature, and unlike electrocaloric effects associated with first-order transitions they are highly reversible in unipolar applied fields. Additionally, the canonical Landau description for strained SrTiO 3 films works well if we set the low-temperature zero-field polarization along one of the in-plane pseudocubic <100> directions. In future, similar strain engineering could be exploited for other films, multilayers and bulk samples to increase the range of electrocaloric materials for energy efficient cooling.

Two thin film deposition routes were studied for the growth of high quality single crystalline Ru (0001) epitaxial films on c-Al2O3 substrates using radio frequency-magnetron sputtering. Such films are very important as buffer layers for the deposition of epitaxial non-collinear antiferromagnetic Mn3X films. The first route involved depositing Ru at 700 °C, leading to a smooth 30 nm thick film. Although, high resolution x-ray diffraction revealed twinned Ru film orientations, in situ post-annealing eliminated one orientation, leaving the film orientation aligned with the substrate, with no in-plane lattice rotation and a large lattice mismatch (13.6%). The second route involved the deposition of Ru at room temperature followed by in situ post-annealing at 700 °C. Transmission electron microscopy confirmed a very high quality of these films, free of crystal twinning, and a 30° in-plane lattice rotation relative to the substrate, resulting in a small in-plane lattice mismatch of –1.6%. X-ray reflectivity demonstrated smooth surfaces for films down to 7 nm thickness. 30 nm thick high quality single-crystalline Mn3Ga and Mn3Sn films were grown on top of the Ru buffer deposited using the second route as a first step to realize Mn3X films for antiferromagnetic spintronics applications.

These data originated from electrical transport and structural characterisation of SRO214 thin films. The dataset includes the following folders. 'Figures' and 'Supplementary': Origin files corresponding to each figure with the raw/calculated data and all the TEM and SEM images that appear in the text. 'Calculations and raw data': original files of raw data and an EXCEL file including relevant calculations for the figures of the paper.

Epitaxial films may be released from growth substrates and transferred to structurally and chemically incompatible substrates, but epitaxial films of transition metal perovskite oxides have not been transferred to electroactive substrates for voltage control of their myriad functional properties. Here we demonstrate good strain transmission at the incoherent interface between a strain-released film of epitaxially grown ferromagnetic La 0.7 Sr 0.3 MnO 3 and an electroactive substrate of ferroelectric 0.68Pb(Mg 1/3 Nb 2/3 )O 3 -0.32PbTiO 3 in a different crystallographic orientation. Our strain-mediated magnetoelectric coupling compares well with respect to epitaxial heterostructures, where the epitaxy responsible for strong coupling can degrade film magnetization via strain and dislocations. Moreover, the electrical switching of magnetic anisotropy is repeatable and non-volatile. High-resolution magnetic vector maps reveal that micromagnetic behaviour is governed by electrically controlled strain and cracks in the film. Our demonstration should inspire others to control the physical/chemical properties in strain-released epitaxial oxide films by using electroactive substrates to impart strain via non-epitaxial interfaces.

Zr2AlC MAX phase-based ceramic material with 33 wt% ZrC has been irradiated with 22 MeV Au7+ ions between room temperature and 600 degrees C, achieving a maximum nominal midrange dose of 3.5 displacements per atom. The response of the material to irradiation has been studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Under room temperature irradiation, the ions caused a partial amorphisation of the MAX phase. At high temperatures, irradiated Zr2AlC remained crystalline, but developed an increased density of dislocations and stacking faults in the (0001) basal planes. The irradiated material also exhibited a temperature-dependent microcracking phenomenon similar to that previously reported in other MAX phase materials. (C) 2019 Published by Elsevier B.V.

Porous GaN distributed Bragg reflectors (DBRs) provide strain-free, high-reflectivity structures with a wide range of applications across nitride optoelectronics. Structural characterization of porous DBRs is currently predominantly achieved by cross-sectional scanning electron microscopy (SEM), which is a destructive process that produces local data and has accuracy limited to around 3% by instrument calibration uncertainty. Here, we show that high-resolution x-ray diffraction (XRD) offers an alternative, nondestructive method for characterizing porous nitride structures. XRD scans of porous GaN DBRs show that despite the constant lattice parameter across the DBR layers, characteristic satellite peaks still arise, which are due to the interference between x-rays reflected from the porous and nonporous layers. By comparing the intensities and positions of the satellite peaks through diffraction patterns simulated from a kinematic model, the structural properties of the porous GaN DBRs can be analyzed. Using our method, we have measured a series of DBRs with stop bands from the blue wavelength region to the IR and compared their structural values with those from SEM data. Our results show that the XRD method offers improvements in the accuracy of determining layer thickness, although uncertainty for the value of porosity remains high. To verify the results gained from the XRD and SEM analysis, we modeled the optical reflectivity using the structural values of both methods. We found that the XRD method offered a better fit to the optical data. XRD, therefore, offers accurate, nondestructive characterization of porous DBR structures based on macroscale measurements and is suitable for full wafer analysis.

We present a comprehensive study of the crystal structure of the thin-film, ferromagnetic topological insulator (Bi, Sb) 2− x V x Te 3 . The dissipationless quantum anomalous Hall edge states it manifests are of particular interest for spintronics, as a natural spin filter or pure spin source, and as qubits for topological quantum computing. For ranges typically used in experiments, we investigate the effect of doping, substrate choice and film thickness on the (Bi, Sb) 2 Te 3 unit cell using high-resolution X-ray diffractometry. Scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements provide local structural and interfacial information. We find that the unit cell is unaffected in-plane by vanadium doping changes, and remains unchanged over a thickness range of 4–10 quintuple layers (1 QL ≈ 1 nm). The in-plane lattice parameter ( a ) also remains the same in films grown on different substrate materials. However, out-of-plane the c -axis increases with the doping level and thicknesses >10 QL, and is potentially reduced in films grown on Si (1 1 1).

High-resolution X-ray diffractometry and scanning transmission electron microscopy data, taken on thin films of ferromagnetic topological insulators. The aim of the study was to investigate the influence of substrate choice, film thickness and doping on the unit cell parameters, for a range typically used in electronic devices.

As charge carriers traverse a single superconductor ferromagnet interface, they experience an additional spin-dependent phase angle that results in spin mixing and the formation of a bound state called the Andreev bound state. Here we explore whether point contact Andreev reflection can be used to detect the Andreev bound state and, within the limits of our experiment, we extract the resulting spin mixing angle. By examining spectra taken from La1.15Sr1.85Mn2O7-Pb junctions, together with a compilation of literature data on highly spin polarized systems, we suggest that the existence of the Andreev bound state would resolve a number of long standing controversies in the literature of Andreev reflection, as well as defining a route to quantify the strength of spin mixing at superconductor-ferromagnet interfaces. Intriguingly, we find that for high transparency junctions, the spin mixing angle appears to take a relatively narrow range of values across all the samples studied. The ferromagnets we have chosen to study share a common property in terms of their spin arrangement, and our observations may point to the importance of this property in determining the spin mixing angle under these circumstances.

Superconducting c-axis-oriented Sr2RuO4 thin film has been fabricated using pulsed laser deposition. Although the superconductivity is localized, the onset critical temperature is enhanced over the bulk value. X-ray microstructural analysis of Sr2RuO4 superconducting and non-superconducting thin films suggests the existence of the localized stacking faults and an overall c-axis lattice expansion which may account for the locally enhanced superconductivity.

Semi-polar group III nitrides and their alloys (AlGaN, InGaN) show great promise for future opto-electronic devices. For these orientations, specific X-ray diffraction (XRD) methods have been developed to measure the alloy content. The XRD methods proposed in the literature all use approximations at different levels. Here, we introduce a novel exact model, against which we compare each simplifying assumption previously used. The relevant approximations are then assembled to produce an accurate linearized model, which shares the same mathematical form as that of the standard polar or non-polar nitride analysis. This linearized model can be further simplified to provide an analytic expression for correction of the alloy content when a tilt (partial relaxation) is found between the alloy epilayer and the semi-polar GaN template. For a given model—alloy content and tilt angle— we can compute the expected XRD data. Vice-versa, the alloy content can be obtained from the experimental measurements—tilt angle and difference in d-spacing. This work focuses on the typical semi-polar planes studied in the literature: inclined a-planes (hh2h¯l), e.g., (112¯2), and inclined m-planes (hh¯0l), e.g., (11¯01) or (22¯01).

There is increasing interest in III-nitride films and multiple quantum well structures grown in non-polar or semi-polar orientations for application in light-emitting devices. We describe a method to obtain the compositions and the thicknesses of layers within III-nitride quantum well or superlattice structures grown in non-polar or semi-polar orientations, based on X-ray scattering. For each new crystallographic orientation considered, new axes were obtained and both the lengths and angles of these new axes calculated relative to the original conventional reference axes. These angles provide the coefficients of the matrix to transform the elastic constants published in the conventional setting (as used for polar c-plane oriented III-nitrides) into the appropriate new values. The new characteristic lengths and new elastic constants are then put into the general equation that relates the composition of a fully strained layer to the experimentally measured out-of-plane alloy d-spacing. Thus we have (a) determined the alloy composition from the difference between the experimentally measured alloy d-spacing and that of the substrate and (b) calculated the strained d-spacing for a given alloy composition for input to simple kinematical simulation software. In addition for quantum well structures the thickness ratio of well-to-barrier must be determined. Here we use the minima in the low angle reflectivity data. The repeat thickness and thus the thicknesses of the well and barrier layers, can be obtained from either the low or the high-angle data. We then cross-check by comparing the experimental and the simulated high-angle diffraction data. This method has been applied successfully to heteroepitaxial non-polar and semi-polar GaN/AlGaN and InGaN/GaN multiple quantum well structures and may also be used to find the composition of epilayers. The method works even in the presence of tilt between the superlattice and the GaN “template’, although in this case additional high-angle diffraction data at different settings must be collected.

Large thermal changes driven by a magnetic field have been proposed for environmentally friendly energy-efficient refrigeration, but only a few materials that suffer hysteresis show these giant magnetocaloric effects. Here we create giant and reversible extrinsic magnetocaloric effects in epitaxial films of the ferromagnetic manganite La(0.7)Ca(0.3)MnO(3) using strain-mediated feedback from BaTiO(3) substrates near a first-order structural phase transition. Our findings should inspire the discovery of giant magnetocaloric effects in a wide range of magnetic materials, and the parallel development of nanostructured bulk samples for practical applications.

We have used electron spin resonance to study an epitaxial thin-film sample of the manganite La0.6Ca0.4MnO3 in which ferromagnetic and paramagnetic phases were previously shown to coexist [Phys. Rev. B 78, 054409 (2008)]. Resonant absorbtions arise on either side of the paramagnetic resonance and reveal that the ferromagnetic phase is itself phase separated into regions with Curie temperatures of similar to 190 and similar to 250 K. This extra complexity is attributed to the coexistence of strained and relaxed regions, as verified by x-ray diffraction.

We report the observation of intrinsic exchange hardening in polycrystalline GdN thin films grown at room temperature by magnetron sputtering. We find, in addition to the ferromagnetic phase, that a fraction of GdN crystallizes in a structural polymorphic form which orders antiferromagnetically. The relative fraction of these two phases was controlled by varying the relative abundance of reactive species in the sputtering plasma by means of the sputtering power and N2 partial pressure. An exchange bias of ∼ 30 Oe was observed at 10 K. The exchange coupling between the ferromagnetic and the antiferromagnetic phases resulted in an order of magnitude enhancement in the coercive field in these films.

A novel rf sputtering technology in which a high density plasma is created in a remote chamber has been used to reactively deposit zinc oxide (ZnO) and indium zinc oxide (IZO) thin films at room temperature from metallic sputtering targets at deposition rates ∼50 nm min−1, which is approximately an order of magnitude greater than that of rf magnetron sputtering. Thin film transistors have been fabricated using IZO with a maximum processing temperature of 120 °C, which is defined by the curing of the photoresist used in patterning. Devices have a saturated field effect mobility of 10 cm2 V−1 s−1 and a switching ratio in excess of 106. Gate bias stress experiments performed at elevated temperatures show a consistent apparent increase in the field effect mobility with time, which is attributed to a charge trapping phenomenon.

The magnetic remanent states and switching behavior of Fe thin-film split-rings are investigated using magnetic force microscopy, magnetoresistance measurements, and micromagnetic simulations in order to assess their suitability as spin-filter contacts for spin field-effect-transistors. The gaps between the two halves of each ring are found to absorb then emit domain walls and act as pinning sites for “virtual” domain walls so that the observed switching mechanisms are similar to those of continuous rings. It is shown that these rings offer advantages over rectangular spin-filter contacts owing to their reduced stray fields and easy accessibility of the necessary magnetic states.