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We demonstrate on prototypical samples containing a ferroelectric layer (BaTiO3/Nb:SrTiO3) that the efficiency of the system, used as photoanode, substantially depends on the polarization state of the ferroelectric layer. We show a significant increase of the photocurrent by a factor larger than 2 when the BaTiO3 film is downward polarized. We explain this finding by the presence of an internal electric field which favors the separation of photo-generated charges. [ABSTRACT FROM AUTHOR]

Epitaxial La0.67Sr0.33MnO3 films grown on orthorhombic NdGaO3 (0 0 1) substrates show predominantly uniaxial magnetic anisotropy. On cooling, we observe the growth of a biaxial contribution, which we quantify by fitting magnetometry data to a coherent rotation model. A film grown under deliberately sub-optimal conditions shows a relatively stronger biaxial contribution that results in a significant population of transverse magnetic domains below ~200 K, as revealed by photoemission electron microscopy with x-ray magnetic circular dichroism contrast. Care should be taken to avoid these transverse domains in spintronic devices designed to exploit the high low-temperature spin-polarization of La0.67Sr0.33MnO3. [ABSTRACT FROM AUTHOR]

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 La0.7Ca0.3MnO3 using strain-mediated feedback from BaTiO3 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. [ABSTRACT FROM AUTHOR]

Results of domain structures observation of individual Ni80 Fe20 and Co sublayers in sputter deposited (NIFe/Au/Co/Au)io multilayers, using an element-sensitive method: the photoemission electron microscopy combined with soft X-ray magnetic circular dichroism, are presented. Also, overall domain structures were studied with magnetic force microscopy. The studies allowed us to reveal submicron stripe domains in the investigated samples and the replication of the stripe domains from the Co layers with perpendicular anisotropy to the NiFe layers with easy-plane anisotropy. [ABSTRACT FROM AUTHOR]

Abstract: As a diluted magnetic semiconductor (DMS), (Ga,Mn)As is a possible candidate for the realization of spintronics devices, due to its intrinsic compatibility with GaAs based electronics. The low Curie temperature still limits its use for practical devices. Despite the huge knowledge on GaAs surface, the (Ga,Mn)As surface is still not well understood and difficult to handle. Standard surface cleaning techniques have many drawbacks, mainly because thermal treatments changes crystal structure. We will compare the magnetic and spectroscopic properties of differently processed (Ga,Mn)As surfaces with X-ray photoemission (XPS), X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD). Samples as-grown, chemically etched, Ar+ sputtered and annealed in oxygen will be compared. [Copyright &y& Elsevier]

Abstract: We have investigated how the surface magnetism of epitaxial La0.67Sr0.33MnO3 films on NdGaO3 substrates is modified by 2nm-thick caps of the undoped manganite LaMnO3 and the band insulator SrTiO3. Low-temperature photoemission electron microscopy images with x-ray magnetic circular dichroism contrast reveal large ferromagnetic domains, and a reduction of surface Curie temperature by 40K (LaMnO3 cap) and 70K (SrTiO3 cap). We use these negative results to argue that capped films of sub-optimally doped La1−x Sr x MnO3 (x≠0.33) should improve the operating temperature of all-oxide and other spintronic devices. [Copyright &y& Elsevier]

The authors have developed a fabrication process of nanocrystalline γ′-FeNiN[220] thin ferromagnetic films by using a dual ion beam sputtering system. The films show well defined in-plane magnetic uniaxial anisotropy, with high anisotropy field and high macroscopic saturation magnetization, requisites of crucial importance for high-frequency applications. The estimated ferromagnetic resonance frequency goes within the gigahertz regime, and the magnetic response can be tailored by the deposition conditions. Element-selective measurements reveal a reduction of the total Fe and Ni magnetic moments in γ′-FeNiN with respect to pure Fe and Ni due to hybridization between Fe and Ni 3d and N 2p states. [ABSTRACT FROM AUTHOR]

We investigate the role of lithographically-induced strain relaxation in a micron-scaled device fabricated from epitaxial thin films of the magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic patterning induces a magnetic anisotropy that competes with the magnetocrystalline and shape induced anisotropies to play a crucial role in stabilising a flux-closing domain pattern. We use magnetic imaging, micromagnetic calculations and linear elastic modelling to investigate a region close to the edges of an etched structure. This highly-strained edge region has a significant influence on the magnetic domain configuration due to an induced magnetic anisotropy resulting from the inverse magnetostriction effect. We investigate the competition between the strain-induced and shape-induced anisotropy energies, and the resultant stable domain configurations, as the width of the bar is reduced to the nanoscale range. Understanding this behaviour will be important when designing hybrid magneto-electric spintronic devices based on highly magnetostrictive materials. [ABSTRACT FROM AUTHOR]

We report on current-induced domain wall motion in Ta/CO20Fe60B20/MgO nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient D = +0.06 mJ/m2. The positive DMI coefficient is interpreted to be a consequence of B diffusion into the Ta buffer layer during annealing, which was observed by chemical depth profiling measurements. The experimental results are compared to one-dimensional model simulations including the effects of pinning. This modeling allows us to reproduce the experimental outcomes and reliably extract a spin-Hall angle θSH = -0.11 for Ta in the nanowires, showing the importance of an analysis that goes beyond the model for perfect nanowires. [ABSTRACT FROM AUTHOR]

Abstract: Core level photoelectron spectroscopy has been used to investigate the effect of substrate doping on the binding energies of 1nm HfO2/0.6nm SiO2/Si films. A characteristic 0.26–0.30nm Hf0.35Si0.65O2 silicate interface is formed between the gate oxide and the SiO2 layer with an equivalent oxide thickness of 0.5nm. High substrate doping shifts the Fermi level upwards by 0.5eV. An interface dipole forms giving rise to a shift in the local work function. Screening from substrate electrons is confined to the SiO2/Si interface. The principal contributions modifying the core level binding energies in the oxide are the doping dependant Fermi level position and the interface dipole strength. [Copyright &y& Elsevier]

We investigate the role of lithographically-induced strain relaxation in a micron-scaled device fabricated from epitaxial thin films of the magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic patterning induces a magnetic anisotropy that competes with the magnetocrystalline and shape induced anisotropies to play a crucial role in stabilising a flux-closing domain pattern. We use magnetic imaging, micromagnetic calculations and linear elastic modelling to investigate a region close to the edges of an etched structure. This highly-strained edge region has a significant influence on the magnetic domain configuration due to an induced magnetic anisotropy resulting from the inverse magnetostriction effect. We investigate the competition between the strain-induced and shape-induced anisotropy energies, and the resultant stable domain configurations, as the width of the bar is reduced to the nanoscale range. Understanding this behaviour will be important when designing hybrid magneto-electric spintronic devices based on highly magnetostrictive materials. [ABSTRACT FROM AUTHOR]

The physical properties of epitaxial films can fundamentally differ from those of bulk single crystals even above the critical thickness. By a combination of nonresonant x-ray magnetic scattering, neutron diffraction and vector-mapped x-ray magnetic linear dichroism photoemission electron microscopy, we show that epitaxial (111)-BiFeO3 films support submicron antiferromagnetic domains, which are magnetoelastically coupled to a coherent crystallographic monoclinic twin structure. This unique texture, which is absent in bulk single crystals, should enable control of magnetism in BiFeO3 film devices via epitaxial strain. [ABSTRACT FROM AUTHOR]

Magnetic doping of topological insulators (TIs) is a prerequisite for their application as spin-based devices. Using x-ray magnetic circular dichroism (XMCD) we investigate the influence of an ultralow coverage (~0.5% of a monolayer) of magnetic atoms on a TI substrate. For Fe and Co adatoms on Bi2Te3 at ~1.5 K we find an orbital-to-spin magnetic moment ratio of ~0.45. The magnetization curve of the Fe atoms recorded by XMCD is in quantitative agreement with a paramagnetic behavior with no indication of long-range magnetic order. The spectral shape of the XMCD indicates that the adatoms are weakly hybridized with the substrate and form narrowband states. The results show that the adatoms are not capable of breaking time-reversal symmetry. [ABSTRACT FROM AUTHOR]

The nanoparticle (NP) redox state is an important parameter in the performance of cobalt-based Fischer-Tropsch synthesis (FTS) catalysts. Here, the compositional evolution of individual CoNPs (6-24 nm) in terms of the oxide vs metallic state was investigated in situ during CO/syngas treatment using spatially resolved X-ray absorption spectroscopy (XAS)/X-ray photoemission electron microscopy (X-PEEM). It was observed that in the presence of CO, smaller CoNPs (i.e., ≤12 nm in size) remained in the metallic state, whereas NPs ≥ 15 nm became partially oxidized, suggesting that the latter were more readily able to dissociate CO. In contrast, in the presence of syngas, the oxide content of NPs ≥ 15 nm reduced, while it increased in quantity in the smaller NPs; this reoxidation that occurs primarily at the surface proved to be temporary, reforming the reduced state during subsequent UHV annealing. O K-edge measurements revealed that a key parameter mitigating the redox behavior of the CoNPs were proximate oxygen vacancies (O vac ). These results demonstrate the differences in the reducibility and the reactivity of Co NP size on a Co/TiO 2 catalyst and the effect O vac have on these properties, therefore yielding a better understanding of the physicochemical properties of this popular choice of FTS catalysts., Competing Interests: The authors declare the following competing financial interest(s): Andrew M. Beale is a co-owner of Finden Ltd., a contract research organization that performs characterization studies on functional materials., (© 2023 The Authors. Published by American Chemical Society.)

Nanoscale interconnects are an important component of molecular electronics. Here we use X-ray spectromicroscopy techniques as well as scanning probe methods to explore the self-assembled growth of insulated iron nanowires as a potential means of supplying an earth abundant solution. The intrinsic anisotropy of a TiO 2 (110) substrate directs the growth of micron length iron wires at elevated temperatures, with a strong metal-support interaction giving rise to ilmenite (FeTiO 3 ) encapsulation. Iron nanoparticles that decorate the nanowires display magnetic properties that suggest other possible applications.

Improving both the extent of metallic Co nanoparticle (Co NP) formation and their stability is necessary to ensure good catalytic performance, particularly for Fischer-Tropsch synthesis (FTS). Here, we observe how the presence of surface oxygen vacancies (O vac ) on TiO 2 can readily reduce individual Co 3 O 4 NPs directly into CoO/Co 0 in the freshly prepared sample by using a combination of X-ray photoemission electron microscopy (X-PEEM) coupled with soft X-ray absorption spectroscopy. The O vac are particularly good at reducing the edge of the NPs as opposed to their center, leading to smaller particles being more reduced than larger ones. We then show how further reduction (and O vac consumption) is achieved during heating in H 2 /syngas (H 2 + CO) and reveal that O vac also prevents total reoxidation of Co NPs in syngas, particularly the smallest (∼8 nm) particles, thus maintaining the presence of metallic Co, potentially improving catalyst performance., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Mott transitions in real materials are first order and almost always associated with lattice distortions, both features promoting the emergence of nanotextured phases. This nanoscale self-organization creates spatially inhomogeneous regions, which can host and protect transient non-thermal electronic and lattice states triggered by light excitation. Here, we combine time-resolved X-ray microscopy with a Landau-Ginzburg functional approach for calculating the strain and electronic real-space configurations. We investigate V 2 O 3 , the archetypal Mott insulator in which nanoscale self-organization already exists in the low-temperature monoclinic phase and strongly affects the transition towards the high-temperature corundum metallic phase. Our joint experimental-theoretical approach uncovers a remarkable out-of-equilibrium phenomenon: the photo-induced stabilisation of the long sought monoclinic metal phase, which is absent at equilibrium and in homogeneous materials, but emerges as a metastable state solely when light excitation is combined with the underlying nanotexture of the monoclinic lattice., (© 2022. The Author(s).)

The interest in understanding scaling limits of magnetic textures such as domain walls spans the entire field of magnetism from its physical fundamentals to applications in information technologies. Here, we explore antiferromagnetic CuMnAs in which imaging by x-ray photoemission reveals the presence of magnetic textures down to nanoscale, reaching the detection limit of this established microscopy in antiferromagnets. We achieve atomic resolution by using differential phase-contrast imaging within aberration-corrected scanning transmission electron microscopy. We identify abrupt domain walls in the antiferromagnetic film corresponding to the Néel order reversal between two neighboring atomic planes. Our work stimulates research of magnetic textures at the ultimate atomic scale and sheds light on electrical and ultrafast optical antiferromagnetic devices with magnetic field-insensitive neuromorphic functionalities.

Non-collinear spin textures in ferromagnetic ultrathin films are attracting a renewed interest fueled by possible fine engineering of several magnetic interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This allows for the stabilization of complex chiral spin textures such as chiral magnetic domain walls (DWs), spin spirals, and magnetic skyrmions among others. We report here on the behavior of chiral DWs at ultrashort timescale after optical pumping in perpendicularly magnetized asymmetric multilayers. The magnetization dynamics is probed using time-resolved circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). We observe a picosecond transient reduction of the CD-XRMS, which is attributed to the spin current-induced coherent and incoherent torques within the continuously varying spin texture of the DWs. We argue that a specific demagnetization of the inner structure of the DW induces a flow of spins from the interior of the neighboring magnetic domains. We identify this time-varying change of the DW texture shortly after the laser pulse as a distortion of the homochiral Néel shape toward a transient mixed Bloch-Néel-Bloch texture along a direction transverse to the DW., (© 2022. The Author(s).)

Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate that microtwin defects, which develop across the entire thickness of the film and terminate on the surface as characteristic lines, determine the location and orientation of 180 ∘ and 90 ∘ domain walls. The results emphasize the crucial role of nanoscale crystalline defects in determining the AF domains and domain walls, and provide a route to optimizing device performance., (© 2022. The Author(s).)

In the quest for post-CMOS (complementary metal-oxide-semiconductor) technologies, driven by the need for improved efficiency and performance, topologically protected ferromagnetic 'whirls' such as skyrmions 1-8 and their anti-particles have shown great promise as solitonic information carriers in racetrack memory-in-logic or neuromorphic devices 1,9-11 . However, the presence of dipolar fields in ferromagnets, which restricts the formation of ultrasmall topological textures 3,6,8,9,12 , and the deleterious skyrmion Hall effect, when skyrmions are driven by spin torques 9,10,12 , have thus far inhibited their practical implementation. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling, have recently become the subject of intense focus 9,13-19 , but they have yet to be experimentally demonstrated in natural antiferromagnetic systems. Here we realize a family of topological antiferromagnetic spin textures in α-Fe 2 O 3 -an Earth-abundant oxide insulator-capped with a platinum overlayer. By exploiting a first-order analogue of the Kibble-Zurek mechanism 20,21 , we stabilize exotic merons and antimerons (half-skyrmions) 8 and their pairs (bimerons) 16,22 , which can be erased by magnetic fields and regenerated by temperature cycling. These structures have characteristic sizes of the order of 100 nanometres and can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways through which further scaling may be achieved. Driven by current-based spin torques from the heavy-metal overlayer, some of these antiferromagnetic textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature 1,9-11,23 .

A novel method of measuring the core level binding energies of multiple sized nanoparticles on the same substrate is demonstrated using the early stage of Au nanoparticle growth on reduced r-TiO 2 (110). This method employed in situ scanning tunneling microscopy (STM) and microfocused X-ray photoemission spectroscopy. An STM tip-shadowing method was used to synthesize patterned areas of Au nanoparticles on the substrate with different coverages and sizes. Patterns were identified and imaged using a UV photoelectron emission microscope. The Au 4f core level binding energies of the nanoparticles were investigated as a function of Au nanoparticle coverage and size. A combination of initial and final state effects modifies the binding energies of the Au 4f core levels as the nanoparticle size changes. When single Au atoms and Au 3 clusters are present, the Au 4f 7/2 binding energy, 84.42 eV, is similar to that observed at a high coverage (1.8 monolayer equivalent), resulting from a cancellation of initial and final state effects. As the coverage is increased, there is a decrease in binding energy, which then increases at a higher coverage to 84.39 eV. These results are consistent with a Volmer-Weber nucleation-growth model of Au nanoparticles at oxygen vacancies, resulting in electron transfer to the nanoparticles.

Antiferromagnets have several favourable properties as active elements in spintronic devices, including ultra-fast dynamics, zero stray fields and insensitivity to external magnetic fields 1 . Tetragonal CuMnAs is a testbed system in which the antiferromagnetic order parameter can be switched reversibly at ambient conditions using electrical currents 2 . In previous experiments, orthogonal in-plane current pulses were used to induce 90° rotations of antiferromagnetic domains and demonstrate the operation of all-electrical memory bits in a multi-terminal geometry 3 . Here, we demonstrate that antiferromagnetic domain walls can be manipulated to realize stable and reproducible domain changes using only two electrical contacts. This is achieved by using the polarity of the current to switch the sign of the current-induced effective field acting on the antiferromagnetic sublattices. The resulting reversible domain and domain wall reconfigurations are imaged using X-ray magnetic linear dichroism microscopy, and can also be detected electrically. Switching by domain-wall motion can occur at much lower current densities than those needed for coherent domain switching.

The growth and reactive dewetting of ultrathin films of iron oxides supported on Re(0001) surfaces have been imaged in situ in real time. Initial growth forms a nonmagnetic stable FeO (wüstite like) layer in a commensurate network upon which high aspect ratio nanowires of several microns in length but less than 40 nm in width can be fabricated. The nanowires are closely aligned with the substrate crystallography and imaging by X-ray magnetic circular dichroism shows that each contain a single magnetic domain. The driving force for dewetting appears to be the minimization of strain energy of the Fe 3 O 4 crystallites and follows the Tersoff and Tromp model in which strain is minimized at constant height by extending in one epitaxially matched direction. Such wires are promising in spintronic applications and we predict that the growth will also occur on other hexagonal substrates.

Insertion devices are utilized at synchrotron radiation facilities around the world for their capability to provide a high-brilliance X-ray beam. APPLE-II type undulators are especially important for their capacity to switch between a variety of photon beam polarization states. A high-precision soft X-ray polarimeter has been used to investigate the polarization calibration of an APPLE-II undulator (period length λ u = 64 mm) installed on beamline I06 at Diamond Light Source. Systematic measurement of the beam polarization state at a range of linear arbitrary angles has been compared with the expected result for a given set of undulator gap and row phase parameters calculated from theory. Determination of the corresponding Stokes-Poincaré parameters from the measured data reveals a discrepancy between the two. The limited number of energy/polarization combinations included in the undulator calibration tables necessitates the use of interpolated values for the missing points which is expected to contribute to the discrepancy. However, by modifying the orbit of the electron beam through the undulator by at least 160 µm it has been found that for certain linear polarizations the discrepancies can be corrected. Overall, it is suggested that complete correction of the Stokes-Poincaré parameters for all linear angles would require alteration of both these aspects.

MnAs epitaxial thin films on GaAs(001) single crystalline substrates crystallize at room temperature (RT) in a mixture of two crystalline phases with distinct magnetic properties, organized as stripes along the MnAs [0001] direction. This particular morphology is driven by anisotropic epitaxial strain. We elucidate here the physical mechanisms at the origin of size reduction effect on the MnAs crystalline phase transition. We investigated the structural and magnetic changes in MnAs patterned microstructures (confined geometry) when the lateral dimension is reduced to values close to the periodicity and width of the stripes observed in continuous films. The effects of the microstructure's lateral size, shape and orientation (with respect to the MnAs [Formula: see text] direction) were characterized by local probe synchrotron X-ray diffraction (μ-XRD) using a focused X-ray beam, X-ray Magnetic Circular Dichroïsm - Photo Emission Electron Microscopy (XMCD-PEEM) and Low Energy Electron Microscopy (LEEM). Changes in the transition temperature and the crystalline phase distribution inside the microstructures are evidenced and quantitatively measured. The effect of finite size and strain relaxation on the magnetic domain structure is also discussed. Counter-intuitively, we demonstrate here that below a critical microstructure size, bulk MnAs structural and magnetic properties are restored. To support our observations we developed, tested and validated a model based on the size-dependence of the elastic energy and strain relaxation to explain this phase re-distribution in laterally confined geometry.

Exploiting multiferroic BiFeO 3 thin films in spintronic devices requires deterministic and robust control of both internal magnetoelectric coupling in BiFeO 3 , as well as exchange coupling of its antiferromagnetic order to a ferromagnetic overlayer. Previous reports utilized approaches based on multi-step ferroelectric switching with multiple ferroelectric domains. Because domain walls can be responsible for fatigue, contain localized charges intrinsically or via defects, and present problems for device reproducibility and scaling, an alternative approach using a monodomain magnetoelectric state with single-step switching is desirable. Here we demonstrate room temperature, deterministic and robust, exchange coupling between monodomain BiFeO 3 films and Co overlayer that is intrinsic (i.e., not dependent on domain walls). Direct coupling between BiFeO 3 antiferromagnetic order and Co magnetization is observed, with ~ 90° in-plane Co moment rotation upon single-step switching that is reproducible for hundreds of cycles. This has important consequences for practical, low power non-volatile magnetoelectric devices utilizing BiFeO 3 .