We have studied ferromagnetic resonance in amorphous trilayers of Cox(Al0.70Zr0.30)1-x. The trilayer composition is such that the outer layers are ferromagnetic, with distinct resonance frequencies, while the spacer layer composition is nominally paramagnetic. We observe two precessional modes, acoustic and optical, and follow these as the interlayer exchange coupling, mediated by a strong proximity-induced magnetization in the spacer, is varied by changing the spacer layer thickness. We find that both the interlayer exchange coupling and the induced magnetization have an exponential decay profile within the spacer, with contrasting decay lengths of lambda IEC = 0.44 nm and lambda PIM = 3.1 nm. This contrast exposes the difference in decay length of spin stiffness, reflected in resonance experiments, and proximity-induced magnetization or polarizability in these amorphous trilayers, from static magnetization measurements.

The production of electrolytic hydrogen or Green Hydrogen has attracted the attention of scientists as a potential enabler of sustainable energy production. The cleavage of the water molecule requires high energy, in order to produce hydrogen and oxygen through their corresponding half reactions, the hydrogen evolution and oxygen evolution reactions. This latter reaction has been studied in more detail, since its slow kinetics make the water electrolysis less efficient, and, for instance, delay the formation of hydrogen in the counter compartment of the electrolytic cell. In this work, a study of the oxygen evolution reaction is presented. For this, a series of rhenium catalysts deposited onto stainless steel 316 are studied with the aim of analyzing the effect of the pure metal (Re) and the metal with heteroatoms (Re-C, Re-B, and Re-O). As one of the problems worldwide is the scarcity of freshwater, the study focuses on the performance of this series of catalysts in highly saline environments, representative of seawater. The synthesis and electrochemical performance is shown, giving high expectations that these electrocatalysts could be potential electrocatalysts in marine environments.

The magnetic properties of amorphous thin films are shaped by inherent composition variations and magnetic proximity effects. Their magnetic properties can be tuned precisely with composition over a continuous range and their high resistance reduces shunting in spintronic systems. We examine the static and dynamic magnetic properties of amorphous magnetic thin films of Cox(Al0.7Zr0.3)1−x in the range $$0.60\le x<0.87$$ , with and without a purposely modulated composition. The Gilbert damping is very low but increases dramatically with decreasing Co content. Damping is also studied in a CoAlZr multilayer with alternating intrinsically paramagnetic and ferromagnetic layers, and a film with a continuously modulated composition, both showing low damping. The structural and magnetic depth profiles of the heterostructures are measured with XRR and PNR, where proximity-induced magnetization is observed in the paramagnetic constituents. The enhancement in magnetization and reduction in damping is equivalent to an increase in mean Co content of approximately 3.4 at% and 1.9 at% for the multilayer and continuously modulated film, respectively. The results demonstrate how composition modulations affect the static and dynamic properties of thin films and how the magnetic proximity effect reduces the impact of such variations in composition.

The electrocatalytic nitrogen reduction reaction (NRR) to ammonia offers a sustainable alternative to the Haber-Bosch process. Vanadium oxynitrides (VON) have been proposed in simulations as promising NRR catalysts via the Mars-van Krevelen mechanism. However, investigating nitrogen-containing materials for NRR is challenging due to possible instability-driven nitrogen leaching. Hence, well-designed and rigorous experiments are crucial to evaluate the stability and activity of such materials under NRR operation. To address this, operando measurements are conducted on VON thin films to assess metal dissolution (stability) and NH3 production (activity). This study introduces a modified stability number (S-number) to quantify ammonia produced per dissolved metal ions. VO0.19N0.81 exhibits an S-number over four times higher in N2 than in Ar, indicating improved stability under NRR conditions. While Faradaic efficiencies remain low (1-2%), steady ammonia production is observed for over 1.5 h, suggesting potential catalytic activity. Furthermore, the simulations indicate refilling of surface vacancies is more favorable when lattice oxygen is present, offering a mechanistic understanding of enhanced stability of VON in N2 compared to Ar. The study paves the way for the development of more stable catalysts and introduces new metrics into the NRR field to facilitate the reporting of trustworthy results.

This study investigates magnetic domains in Fe/Si and Fe/Si + B4C multilayers using spin flip off-specular polarized neutron reflectometry. The results show that Fe/Si multilayers exhibit pronounced spin flip off-specular scattering originating from magnetic domains that are uncorrelated out of plane. With increasing external magnetic field the domains progressively coalesce and their magnetization rotates toward alignment with the applied field, approaching a homogeneous magnetic state at higher fields. In contrast, Fe/Si + B4C multilayers exhibit no detectable spin flip off-specular scattering already at low fields, indicating that the multilayer reaches magnetic saturation at significantly lower applied fields. The scattering patterns are interpreted using distorted wave Born approximation simulations in BornAgain, enabled by our added code for simulating magnetic domains and magnetic ordering. To further probe the magnetic behavior, low-energy mu+SR measurements were performed, representing the first mu+SR investigation of polarizing neutron optics multilayers. Together with comparison to previously reported VSM data, these measurements provide insight into the magnetic behavior across short range, medium range, and long range length scales. The results show that incorporating approximately 15 vol.

i-MAX phases are quaternary variants of the nanolaminated MAX phases, with additional in-plane ordering of the M atoms. The combination of in-plane and out-of-plane ordering potentially gives rise to complex magnetic behaviour. The i-MAX phase (Mn2/3Sc1/3)2GaC has been synthesized in epitaxial thin film form on three different substrates, SiC-4H(001), MgO(111) and Al2O3(0001), by magnetron sputtering using elemental targets. Structural characterization by x-ray scattering and scanning transmission electron microscopy confirms the phase on all three substrates, although the highest crystal quality is obtained on SiC-4H(001). Highresolution images reveal the distinctive i-MAX structure, which is orthorhombic of space group Cmcm. Magnetic characterization reveals that the ground state is most likely antiferromagnetic. This confirms previous theoretical calculations which predicted an antiferromagnetic ground state and establishes the (Mn2/3Sc1/3)2GaC i-MAX phase as a potential candidate for antiferromagnetic spintronic applications.

The concept of scattering length density tuning for improved polarization is investigated for Fe/B411CTi multilayers and compared to the commonly used Fe/Si system in polarizing multilayer neutron optics. X-ray and neutron reflectivity, magnetization, and neutron polarization were measured on such multilayers, highlighting differences from conventional Fe/Si multilayers. The multilayer systems were deposited with 25 Å period thickness, a layer thickness ratio of 0.35, and 20 periods using ion-assisted dc magnetron sputtering. Replacing Si with B411CTi for these multilayers showed an increase in reflectivity due to a reduction in interface width. Tuning the ratio between B411C and Ti in the nonmagnetic layers enabled a wide range of scattering length density contrasting and matching for spin-down neutrons, which in turn led to an improved polarization. These findings demonstrate the potential of Fe/B411CTi multilayers as a promising option for polarizing neutron optics and highlight the concept of scattering length density tuning in a large range using B411CTi. Published by the American Physical Society 2024

The utilization of polarized neutrons is of great importance in scientific disciplines spanning materials science, physics, biology, and chemistry. However, state-of-the-art multilayer polarizing neutron optics have limitations, particularly low specular reflectivity and polarization at higher scattering vectors/angles, and the requirement of high external magnetic fields to saturate the polarizer magnetization. Here, we show that, by incorporating 11B4C into Fe/Si multilayers, amorphization and smooth interfaces can be achieved, yielding higher neutron reflectivity, less diffuse scattering, and higher polarization. Magnetic coercivity is eliminated, and magnetic saturation can be reached at low external fields (>2 militesla). This approach offers prospects for substantial improvement in polarizing neutron optics with nonintrusive positioning of the polarizer, enhanced flux, increased data accuracy, and further polarizing/analyzing methods at neutron scattering facilities.

The utilization of polarized neutrons is of great importance in scientific disciplines spanning materials science, physics, biology, and chemistry. However, state-of-the-art multilayer polarizing neutron optics have limitations, particularly low specular reflectivity and polarization at higher scattering vectors/angles, and the requirement of high external magnetic fields to saturate the polarizer magnetization. Here, we show that, by incorporating 11 B 4 C into Fe/Si multilayers, amorphization and smooth interfaces can be achieved, yielding higher neutron reflectivity, less diffuse scattering, and higher polarization. Magnetic coercivity is eliminated, and magnetic saturation can be reached at low external fields (>2 militesla). This approach offers prospects for substantial improvement in polarizing neutron optics with nonintrusive positioning of the polarizer, enhanced flux, increased data accuracy, and further polarizing/analyzing methods at neutron scattering facilities.

The concept of scattering length density tuning for improved polarization is investigated for Fe/11B4CTi multilayers and compared to the commonly used Fe/Si system in polarizing multilayer neutron optics. X-ray and neutron reflectivity, magnetization, and neutron polarization were measured on such multilayers, highlighting differences from conventional Fe/Si multilayers. The multilayer systems were deposited with 25 & Aring; period thickness, a layer thickness ratio of 0.35, and 20 periods using ion-assisted dc magnetron sputtering. Replacing Si with 11B4CTi for these multilayers showed an increase in reflectivity due to a reduction in interface width. Tuning the ratio between 11B4C and Ti in the nonmagnetic layers enabled a wide range of scattering length density contrasting and matching for spin-down neutrons, which in turn led to an improved polarization. These findings demonstrate the potential of Fe/11B4CTi multilayers as a promising option for polarizing neutron optics and highlight the concept of scattering length density tuning in a large range using 11B4CTi.

The utilization of polarized neutrons is of great importance in scientific disciplines spanning materials science, physics, biology, and chemistry. Polarization analysis offers insights into otherwise unattainable sample information such as magnetic domains and structures, protein crystallography, composition, orientation, ion-diffusion mechanisms, and relative location of molecules in multicomponent biological systems. State-of-the-art multilayer polarizing neutron optics have limitations, particularly low specular reflectivity and polarization at higher scattering vectors/angles, and the requirement of high external magnetic fields to saturate the polarizer magnetization. Here, we show that by incorporating 11B4C into Fe/Si multilayers, amorphization and smooth interfaces can be achieved, yielding higher neutron reflectivity, less diffuse scattering and higher polarization. Magnetic coercivity is eliminated, and magnetic saturation can be reached at low external fields (>2 mT). This approach offers prospects for significant improvement in polarizing neutron optics, enabling; nonintrusive positioning of the polarizer, enhanced flux, increased data accuracy, and further polarizing/analyzing methods at neutron scattering facilities.

We study the magnetic properties of amorphous TbxCo100-xfilms withxin the range 8-12 at% and with a thickness of 5-100 nm. In this range the magnetic properties are shaped by a competition between a perpendicular bulk magnetic anisotropy and an in-plane interface anisotropy, in addition to the changes in magnetization. This results in a temperature controllable spin reorientation transition from in-plane to out-of-plane which is thickness and composition dependent. Furthermore, we show that perpendicular anisotropy is recovered throughout an entire TbCo/CoAlZr multilayer, where neither TbCo nor CoAlZr single layers exhibit perpendicular anisotropy. This illustrates the important role of the TbCo interfaces in the overall effective anisotropy.

Amorphous metal coatings have great potential for corrosion protection but finding alloy compositions which form a stable amorphous structure can be an overwhelming task. We use combinatorial magnetron sputtering and X-ray analysis to map out the phase space of TaSiM (M = Al, Cr, Fe, Ti) alloys in order to identify amorphous compositions. Atomic percentages of above 10-15 at.% of each constituent yield amorphous coatings in all four systems. TaSiAl coatings are stable when annealed in air up to and including 550 degrees C whereas TaSiFe, TaSiCr and TaSiTi remain amorphous up to and including 750 degrees C. In particular, Ta35Si15Cr50 is almost unchanged at that temperature, and has a stable surface oxide shell less than 20 nm in thickness at 650 degrees C. The stability of these materials at high temperatures means that they could be suitable as anti -corrosion coatings in high temperature applications.

Mn2GaC is a MAX phase belonging to a family of naturally nanolaminated materials with formula M(n+1)AX(n) (n = 1, 2, 3), where M is a transition metal, A is an A-group element , X is carbon or nitrogen. It has a complex magnetic phase diagram, , there are many open questions regarding its magnetic properties. Here we study epitaxial films of Mn2GaC with two different crystal orientations on MgO(1 1 1) substrates: a (0 0 0 1) dominated orientation and a mixed (0 0 0 1) and (1 0 (1) over bar 3) orientation. Magnetic measurements between 3 and 320 K are presented for in-plane and out-of-plane magnetic fields on both types of film, which show that Mn2GaC has a magnetocrystalline anisotropy with (0 0 0 1) as easy planes. This provides clear experimental evidence of the anisotropic properties associated with the nanolaminated structure of a MAX phase. In addition, a close look at the magnetic response at low temperature shows that the noncollinear magnetic state is unchanged below 50 K, contrary to previous results, with a magnetic moment of 0.38 mu(B) per Mn atom at a temperature of 3 K and applied field of 5 T.

MAX phases are a class of intrinsically nanolaminated materials, which combine features of metals and ceramics, owing to the alternating metallic and covalent bonding between atomic layers. Magnetic MAX phases have been known for a decade, but ferromagnetism at room temperature in this highly anisotropic system has been elusive, limiting their value as magnets in practice. Here, we show that a MAX phase with a strong ferromagnetic response is obtained by substituting Mn with Cr on the M-site in the well-known Mn2GaC. The ferromagnetic response is observed in (Mn1−xCrx)2GaC with 0.06 < x < 0.29 up to temperatures well exceeding room temperature (489 K). The strongest magnetization is achieved with x = 0.12, reaching a saturation moment of 1.25 μB and a remanence of 0.67 μB per M-atom at 3 K and maintaining 0.90 and 0.44 μB per M-atom, respectively, at 300 K. This is the first experimental report of a significant ferromagnetic response in a MAX phase at room temperature. The results open the door to the use of MAX phases in a broad range of applications, from bulk magnets in power electronics to spintronic devices.

We present a study of the effect of annealing amorphous ferromagnetic thin films of $\text{Co}_{0.85}(\mathrm{A}1_{0.7}\text{Zr}_{0.3})_{0.15}$ , post deposition. The annealing was done in vacuum with no applied magnetic field. We find that already at a relatively low annealing temperature of 130 $^{\circ} \mathrm{C}$ there is crystallite formation that introduces both structural and magnetic inhomogeneity. This does not affect the saturation magnetization strongly, but strongly affects the switching behavior and the overall effective anisotropy of the films. Further, there is a dramatic increase in magnetization damping. Thus, the annealing has a profound effect on both static and dynamic magnetic properties of the material. This is important to keep in mind for potential applications using these materials.

Niobium oxides are a complex materials system and synthesis of a specific crystal phase is challenging. Here, we demonstrate a synthesis route for polycrystalline films of cubic NbO, tetragonal NbO2 and monoclinic Nb2O5, based on reactive dc magnetron sputtering at moderate temperature and post-annealing in vacuum. Varying the O2 flow during deposition is used to tune the stoichiometry and subsequent annealing induces crystal formation. NbO is obtained by growth in 1-2 sccm O2 flow and post-annealing at 600-700 degrees C. NbO2 and Nb2O5 are formed by growth in 3-4 sccm O2 and 6-7 sccm O2 flows, respectively, followed by annealing at 800 degrees C. Prior to annealing the films are amorphous and atomically flat but crystallization during post-annealing results in a substantial increase in roughness and complex surface morphologies. The density of the amorphous films, determined by x-ray reflectivity prior to annealing, is a good predictor of the crystal phase obtained after annealing.

Alkaline seawater electrolysis is a promising method for hydrogen production; however, little progress has been made in investigating the substrates for oxygen evolution reaction (OER) electrocatalysts. Ni foam and stainless-steel mesh (SS mesh) were investigated systematically for OER in alkaline seawater electrolysis in this work. The overpotentials and Tafel slopes with SS meshes are smaller than Ni foams, and it also exhibits excellent stability. Interestingly, the performance of the SS mesh even outperforms various non-noble metal electrocatalysts and is comparable to commercial RuO2 and IrO2. The corrosion conditions of Ni foam and SS mesh electrodes were studied and revealed. Furthermore, the electrochemically active surface area (ECSA) of Ni foam is 12 times higher than SS mesh in the same geometric area, indicating the electrochemical activity of SS mesh is much superior to Ni foam. This work expands on promising substrates for alkaline seawater electrolysis, with cost and performance advantages.

Electrochemical reduction of dinitrogen to ammonia is investigated in a micro-reactor flow-cell using thin films of VN, CrN, NbN and ZrN. Chronoamperometry loops are used for ammonia production analysis. Operando ammonia quantification is accomplished in a flow injection analyzer. Results show the effect of presence/absence of N-2(g) within both the electrochemical characterization and ammonia production for ZrN. However, no ammonia is detected from studies on CrN. VN and NbN are inactivated upon reacting their N atoms of the surface top layer(s). Results obtained from ammonia measurements, electrochemical impedance spectroscopy analysis, surface stability checks, and surface characterization using X-ray reflectivity, reveal certain trends indicating catalytic behavior for ZrN. However, the concentration of produced ammonia is below the detection limit of the methods devised to analyze the samples from isotope labeling experiments. The onset of ammonia production on ZrN appears to be in close agreement with that predicted previously by computational studies. (C) 2022 Elsevier Inc. All rights reserved.