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Abstract: Magnetron sputtering offers a scalable route to magnetic topological insulators (MTIs) based on Cr-doped Sb2Te3. We combine a range of X-ray diffraction (XRD), reciprocal-space mapping (RSM), scanning transmission electron microscopy (STEM), scanning TEM-energy-dispersive X-ray spectroscopy (STEM-EDS), and X-ray absorption spectroscopy, and X-ray magnetic circular dichroism (XAS/XMCD) techniques to study the structure and magnetism of Cr-doped Sb2Te3 films. Symmetric 𝜃 -2𝜃 XRD and RSM establish a solubility window. Layered tetradymite order persists up to ∼10 at.-% Cr, while higher doping yields CrTe/Cr2Te3 secondary phases. STEM reveals nanocrystalline layered stacking at low Cr and loss of long-range layering at higher Cr concentrations, consistent with XRD/RSM. Magnetometry on a 6% film shows soft ferromagnetism at 5 K. XAS and XMCD at the Cr 𝐿2,3 edges exhibits a depth dependence: total electron yield (TE; surface sensitive) shows both nominal Cr2+ and Cr3+, whereas fluorescence yield (FY; bulk sensitive) shows a much higher Cr2+ weight. Sum rules applied to TEY give 𝑚𝐿=(0.20±0.04) 𝜇B /Cr, and 𝑚𝑆=(1.6±0.2) 𝜇B /Cr, whereby we note that the applied maximum field (3 T) likely underestimates 𝑚𝑆 . These results define a practical growth window and outline key parameters for MTI films.

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Abstract: The synthesis and magnetic properties of the intrinsic magnetic topological insulator MnBi2Te4, grown by magnetron sputtering, are investigated. While this growth method enables smoother morphologies than molecular beam epitaxy and is compatible with scalable processing, the metastable nature of MnBi2Te4 presents considerable challenges in phase control and magnetic uniformity. By systematically varying the relative sputter powers of Mn, Bi2Te3, and Te targets, conditions that favor the formation of near-stoichiometric MnBi2Te4, as supported by X-ray diffraction, atomic force microscopy, and energy-dispersive X-ray spectroscopy, are identified. These films exhibit reduce surface roughness and lower twin-domain density compared to Mn-rich counterparts, which show evidence of phase separation and structural disorder. Magnetometry and X-ray magnetic circular dichroism reveal that both film types exhibit sizable Mn moments, although signatures of antiferromagnetic order are only weakly expressed and appear sensitive to composition and morphology. Despite producing structurally well-ordered films, clear linear dichroism attributable to A-type antiferromagnetic ordering is not observed, suggesting magnetic inhomogeneity or suppression of interlayer coupling. These results highlight the compositional sensitivity of sputtered MnBi2Te4 and underline the difficulties in stabilizing the intrinsic magnetic topological phase in thin-film form.

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Abstract: The deposition process of the IrMn3/Co70Fe30 bilayer of antiferromagnet/ferromagnet (AF/FM) type was modified by introducing a nitrogen additive in argon plasma during the magnetron sputtering of the Co70Fe30 layer. This slight modification significantly enhanced the exchange bias energy density and reduced coercivity of an AF/FM bilayer for the AF IrMn layer thickness ranging from 20 to 50 Å. Calculations indicate that the boost in exchange bias energy density and the reduction in coercivity can be attributed to the increased anisotropy energy of the AF layer, resulting in more effective pinning of the FM layer by AF grains. The increase in anisotropy is caused by the diffusion of nitrogen from the FM into the AF layer, as established by x-ray diffraction, neutron reflectometry, and x-ray magnetic circular dichroism. Our research allows us to improve magnetic characteristics of exchange-coupled FM/AF structures through minor modifications in the sputtering process and/or save up to 20% of the costly IrMn3 target by reducing the thickness of the AF layer.

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Abstract: Molecular cerium complexes are of interest due to their remarkable redox and photophysical properties. We have investigated the ligand tunability of the electronic structure and properties of cerium(IV) complexes with functionalized tetradentate N2O2-donor ligands: [CeIV(LtBu)2] (1), [CeIV(LH)2] (2) and [CeIV(LNO2)2] (3), where H2LtBu = bis(2-hydroxy-3,5-di-tert-butylbenzyl)(2-pyridylmethyl)amine, H2LH = bis(2-hydroxybenzyl)(2-pyridylmethyl)amine and H2LNO2 = bis(2-hydroxy-5-nitrobenzyl)(2-pyridylmethyl)amine. These compounds all exhibit a quasi-reversible one-electron reduction to cerium(III), with the redox potential correlating with the electron donor–acceptor characteristics of the ligand substituents. This correlation is rationalized by energy stabilization of the HOMO, as determined by density functional theory calculations, and is consistent with arene π → Ce 4f* ligand-to-metal charge transfer bands. The L3-edge XANES exhibits minimal variation in Ce 4f occupation for the three compounds, which suggests that the 4f covalent character and composition of the ground-state character do not vary significantly across the series. However, M4,5-edge XAS shows charge transfer satellites that subtly differ in shape and energy, indicating small distinctions in ligand-to-metal charge transfer for the compounds, consistent with small differences in temperature-independent magnetism. The ability to modulate the redox and optical properties of cerium complexes through ligand derivatization highlights the potential for customizable molecular cerium catalysts and photocatalysts.