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The detection and quantification of hydrogen is becoming increasingly important in research on electronic materials and devices. Here the authors show that waveguide resonances enhance the sensitivity of neutron reflectometry, enabling fast, direct, and nondestructive measurements of hydrogen incorporation in thin-film structures.

A 63 Å thick film originating from frozen air on a solid substrate has been investigated via neutron reflectometry. The experiment shows that neutron reflectometry allows performing chemical surface analysis by quantifying the composition of this frozen layer and identifies the film to be frozen oxygen. Keywords: Thin films, Surface oxygen layer, Neutron reflectometry

Strontium cobaltite (SrCoO _2.5+ _δ , SCO) is a fascinating material because of its topotactic structural phase transition caused by a change in oxygen stoichiometry. In the brownmillerite phase ( δ = 0) it is an insulating antiferromagnet whereas in the perovskite phase ( δ = 0.5) it is a conducting ferromagnet. In contrast, the impact of the varying Co/Sr stoichiometry on the structure has not yet been studied in SCO thin films. Using molecular beam epitaxy we have fabricated SCO thin films of varying Co/Sr stoichiometry. Films with Co excess exhibit a brownmillerite crystal structure with CoO precipitates within the thin film and on the surface. Co deficient films are amorphous. Only for 1:1 stoichiometry a pure brownmillerite structure is present. We find a clear dependence of the Reflection High Energy Electron Diffraction (RHEED) pattern of these thin films on the stoichiometry. Interestingly, RHEED is very sensitive to a Co excess of less than 12% while x-ray diffraction fails to reveal that difference. Hence, using RHEED, the stoichiometry of SCO can be evaluated and tuned in-situ to a high degree of precision, which allows for a quick adjustment of the growth parameters during a sample series.

The detection and quantification of hydrogen is becoming increasingly important in research on electronic materials and devices, following the identification of the hydrogen content as a potent control parameter for the electronic properties. However, establishing quantitative correlations between the hydrogen content and the physical properties of solids remains a formidable challenge. Here we report neutron reflectometry experiments on 50 nm thick niobium films during hydrogen loading, and show that the momentum-space position of a prominent waveguide resonance allows tracking of the absolute hydrogen content with an accuracy of about one atomic percent on a timescale of less than a minute. Resonance-enhanced neutron reflectometry thus allows fast, direct, and non-destructive measurements of the hydrogen concentration in thin-film structures, with sensitivity high enough for real-time in-situ studies., (© 2022. The Author(s).)

All-oxide-based synthetic antiferromagnets (SAFs) are attracting intense research interest due to their superior tunability and great potentials for antiferromagnetic spintronic devices. In this work, using the La 2/3 Ca 1/3 MnO 3 /CaRu 1/2 Ti 1/2 O 3 (LCMO/CRTO) superlattice as a model SAF, we investigated the layer-resolved magnetic reversal mechanism by polarized neutron reflectivity. We found that the reversal of LCMO layer moments is mediated by nucleation, expansion, and shrinkage of a magnetic soliton. This unique magnetic reversal process creates a reversed magnetic configuration of the SAF after a simple field cycling. Therefore, it can enable vertical data transfer from the bottom to the top of the superlattice. The physical origin of this intriguing magnetic reversal process could be attributed to the cooperation of the surface spin-flop effect and enhanced uniaxial magnetic anisotropy of the bottom LCMO layer. This work may pave a way to utilize all-oxide-based SAFs for three-dimensional spintronic devices with vertical data transfer and high-density data storage.

We have investigated the structural, magnetic and superconduction properties of [Nb(1.5 nm)/Fe( x )] 10 superlattices deposited on a thick Nb(50 nm) layer. Our investigation showed that the Nb(50 nm) layer grows epitaxially at 800 °C on the Al 2 O 3 (1-102) substrate. Samples grown at this condition possess a high residual resistivity ratio of 15-20. By using neutron reflectometry we show that Fe/Nb superlattices with x < 4 nm form a depth-modulated FeNb alloy with concentration of iron varying between 60% and 90%. This alloy has weak ferromagnetic properties. The proximity of this weak ferromagnetic layer to a thick superconductor leads to an intermediate phase that is characterized by a suppressed but still finite resistance of structure in a temperature interval of about 1 K below the superconducting transition of thick Nb. By increasing the thickness of the Fe layer to x = 4 nm the intermediate phase disappears. We attribute the intermediate state to proximity induced non-homogeneous superconductivity in the structure., (Copyright © 2020, Khaydukov et al.; licensee Beilstein-Institut.)

The ability to create atomically perfect, epitaxial heterostructures of correlated complex perovskite oxides using state-of-art thin film deposition techniques has generated new physical phenomena at engineered interfaces. Here we report on the impact of growth kinetics on the magnetic structure and exchange coupling at the interface in heterostructures combining layers of antiferromagnetic La 1/3 Sr 2/3 FeO 3 (LSFO) and ferromagnetic La 2/3 Sr 1/3 MnO 3 (LSMO) on (0 0 1)-oriented SrTiO 3 (STO) substrates. Two growth orders are investigated, (a) LSMO/LSFO/STO(0 0 1) and (b) LSFO/LSMO/STO(0 0 1), where the LSFO layer is grown by molecular beam epitaxy and the LSMO layer by high oxygen pressure sputtering. The interface has been investigated using electron microscopy and polarized neutron reflectometry. Interdiffusion over seven monolayers is observed in LSMO/LSFO (a) with an almost 50% reduction in magnetization at the interface and showing no exchange coupling. However, the exchange bias effect ([Formula: see text] mT at 10 K) could be realized when the interface is atomically sharp, as in LSFO/LSMO (b). Our study therefore reveals that, even for well ordered and lattice-matched structures, the kinetics involved in the growth processes drastically influences the interface quality with a strong correlation to the magnetic properties.

We report on a versatile mini ultra-high vacuum (UHV) chamber which is designed to be used on the MAgnetic Reflectometer with high Incident Angle of the Jülich Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum in Garching, Germany. Samples are prepared in the adjacent thin film laboratory by molecular beam epitaxy and moved into the compact chamber for transfer without exposure to ambient air. The chamber is based on DN 40 CF flanges and equipped with sapphire view ports, a small getter pump, and a wobble stick, which serves also as sample holder. Here, we present polarized neutron reflectivity measurements which have been performed on Co thin films at room temperature in UHV and in ambient air in a magnetic field of 200 mT and in the Q-range of 0.18 Å -1 . The results confirm that the Co film is not contaminated during the polarized neutron reflectivity measurement. Herewith it is demonstrated that the mini UHV transport chamber also works as a measurement chamber which opens new possibilities for polarized neutron measurements under UHV conditions.