Scherrer (Switzerland)

Chemical doping in transition metal oxides drives a complex interplay among lattice, charge, and spin degrees of freedom. Herein, we investigate the structural and magnetic evolution of Nd2-xSrxNiO4+δ (0 ≤ x ≤ 0.7), a layered nickelate system with mixed-valence Ni2+/Ni3+ ions and tunable oxygen nonstoichiometry (δ), using high-resolution synchrotron X-ray and neutron diffraction, complemented by macroscopic measurements over a broad temperature range. High-temperature solid-state synthesis in air promotes oxygen interstitial incorporation, yielding hyper-stoichiometric compounds (δ > 0). For Nd2NiO4.23 (x = 0), excess oxygen atoms exhibit long-range ordering, giving rise to incommensurate structural modulations and a sequence of order-order transitions persisting up to 800 K. Sr substitution disrupts this ordering via Coulombic effects and suppresses both oxygen uptake and NiO6 octahedral tilting. Stripe-like spin ordering emerges at x = 0.25, 0.33, and 0.5. The x = 0.5 sample exhibits magnetic incommensurability (ε ≈ 0.44) below 95 K, indicative of charge discommensuration in NiO2 planes. Unlike the oxygen-doped (x = 0) phase, Sr-doped samples show quasi-two-dimensional magnetism, with in-plane and out-of-plane magnetic correlation lengths of 114(2) Å and 16(3) Å, respectively. These results reveal strong coupling among chemical doping, crystal structure, oxygen ordering, and magnetism in layered nickelates.

Carrier-free 202Tl was thermally separated from proton-irradiated natHgO. Pressed natHgO targets were irradiated with ≈26MeV protons at the IP2 beamline of the high-intensity proton accelerator facility at the Paul Scherrer Institute. The well-known thermal decomposition of HgO at >470∘{470}\\,^\\circ$$\\end{document}]]>C and the strong adsorption of Tl on a Ta surface allowed for a simple and quantitative gas-phase separation of carrier-free Tl from bulk amounts of HgO target material between 550 and 670∘°C. The separation efficiency was verified by γ-spectroscopy via the main γ-emissions of 202Tl and co-produced 203Hg. This method generally provides a fast and reliable preparation of carrier-free, neutron-deficient Tl radioisotopes (e.g., medically relevant 201Tl) from a proton-irradiated natHgO matrix.

Abstract Displacement‐type ferroelectrics usually exclude magnetic d‐electron contribution. Applying a magnetic field thus can little change the electric polarization. Herein, a magnetic ionic driven displacement‐type perovskite ferroelectric CaFe3Ti4O12 is reported. In this compound, magnetic Fe2+ ions contribute to both ferroelectric and antiferromagnetic orders respectively at TC ≈107 and TN ≈ 3.1 K, resulting in coupled electric and magnetic domains. A moderate magnetic field can induce a metamagnetic transition toward ferromagnetic correlations. External magnetic fields can thus readily tune the magnetic and the joint ferroelectric domains, giving rise to exceptional magnetic‐field controllable displacement‐type polarization with a large magnetoelectric (ME) coupling coefficient. This study opens up a new avenue to find unprecedented ME effects in displacement‐type ferroelectrics for numerous applications.

Using heterogeneous single-atom catalysts (SACs) in the Suzuki-Miyaura coupling (SMC) has promising economic and environmental benefits over traditionally applied palladium complexes. However, limited mechanistic understanding hinders progress in their design and implementation. Our study provides critical insights into the working principles of Pd1@C3N4, a promising SAC for the SMC. We demonstrate that the base, ligand, and solvent play pivotal roles in facilitating interface formation with reaction media, activating Pd centers, and modulating competing reaction pathways. Controlling the previously overlooked interplay between base strength, reagent solubility, and surface wetting is essential for mitigating mass transfer limitations in the triphasic reaction system and promoting catalyst reusability. Optimum conditions for Pd1@C3N4 require polar solvents, intermediate base strength, and increased water content. Our investigations reveal that high selectivity requires minimizing competitive coordination of bases and phosphine ligands to the Pd centers, to avoid homocoupling and alternative reductive elimination mechanisms giving rise to phosphonium side-products. Furthermore, in situ XAS investigations probing electronic structures and coordination environments of Pd sites further rationalize the base and ligand coordination, confirming and expanding upon previous computational hypotheses for Pd1@C3N4. This understanding allows for designing a more selective ligand-free reaction pathway using the solvent and base to modulate the chemical environment of the active sites. We highlight the importance of environment-compatible surface tension, the creation of coordinatively available active sites, and the stabilization of partially reduced Pd centers, emphasizing the importance of mechanistic studies to advance the design of SACs in organic liquid phase reactions.

Strongly-correlated transition-metal oxides are widely known for their various exotic phenomena. This is exemplified by rare-earth nickelates such as LaNiO3, which possess intimate interconnections between their electronic, spin, and lattice degrees of freedom. Their properties can be further enhanced by pairing them in hybrid heterostructures, which can lead to hidden phases and emergent phenomena. An important example is the LaNiO3/LaTiO3 superlattice, where an interlayer electron transfer has been observed from LaTiO3 into LaNiO3 leading to a high-spin state. However, macroscopic emergence of magnetic order associated with this high-spin state has so far not been observed. Here, by using muon spin rotation, x-ray absorption, and resonant inelastic x-ray scattering, direct evidence of an emergent antiferromagnetic order with high magnon energy and exchange interactions at the LaNiO3/LaTiO3 interface is presented. As the magnetism is purely interfacial, a single LaNiO3/LaTiO3 interface can essentially behave as an atomically thin strongly-correlated quasi-2D antiferromagnet, potentially allowing its technological utilization in advanced spintronic devices. Furthermore, its strong quasi-2D magnetic correlations, orbitally-polarized planar ligand holes, and layered superlattice design make its electronic, magnetic, and lattice configurations resemble the precursor states of superconducting cuprates and nickelates, but with an S→1 spin state instead.

The surface of three-dimensional materials provides an ideal and versatile platform to explore quantum-confined physics. Here, we systematically investigate the electronic structure of Na-intercalated CrTe2, a van der Waals antiferromagnet, using angle-resolved photoemission spectroscopy and ab initio calculations. The measured band structure deviates from the calculation of bulk NaCrTe2 but agrees with that of ferromagnetic monolayer CrTe2. Consistently, we observe unexpected exchange splitting of the band dispersions, persisting well above the Néel temperature of bulk NaCrTe2. We argue that NaCrTe2 features a quantum-confined 2D ferromagnetic state in the topmost surface layer due to strong ferromagnetic correlation in the CrTe2 layer. Moreover, the exchange splitting and the critical temperature can be controlled by surface doping of alkali-metal atoms, suggesting the feasibility of tuning the surface ferromagnetism. Our work not only presents a simple platform for exploring tunable 2D ferromagnetism but also provides important insights into the quantum-confined low-dimensional magnetic states.

Machine Learning In article number 2301397, Bugaev and co-workers used machine learning algorithms to extract metal-metal interatomic distances in supported palladium hydride nanoparticles from in situ infrared spectra using CO as a probe molecule. This approach can be used as an efficient, cheap, and non-destructive method to characterize the atomic structure of metal catalysts under in situ and operando conditions.

The next generation of experiments on charged lepton flavor violation demands higher muon rates. To achieve this, one of the existing target stations at the Paul Scherrer Institute's high-intensity proton accelerator, along with its two connected beamlines, will be dismantled and rebuilt as part of the High Intensity Muon Beams (HIMB) project, under the Swiss Roadmap for Research Infrastructures initiative, IMPACT. The new MuH2 and MuH3 beamlines will rely on 15 large-aperture solenoids and 5 dipoles for muon beam transport, designed to handle a large phase-space beam. Our estimates of the absorbed dose levels indicate that five transport solenoids and two dipoles must be radiation-resistant, requiring the use of mineral-insulated cables, whilst the other magnets can utilize epoxy-impregnated coils. Currently, the design of transport beamline components is based on standard resistive magnets, which suffer from high power consumption. This study aims to explore an alternative using Nb-Ti superconducting coils to reduce power consumption. The paper focuses on the design study of transport solenoids and includes a thermo-economic analysis, considering radiation exposure at three positions relative to the target.

We consider the full genuine next-to-leading order SUSY–QCD corrections to the charged Higgs decays into quarks supplemented by the NNLO corrections to the effective top and bottom Yukawa couplings. The NNLO corrections to the effective top Yukawa coupling are a new ingredient of our analysis. We arrive at an approximate NNLO prediction for MSSM charged Higgs decays after including the N4LO QCD corrections for large charged Higgs masses. The residual uncertainties are in the percent range or below, depending on the particular MSSM scenario.