Noncollinear spin structures have attracted tremendous attention because they offer a versatile platform for spin control and manipulation, essential in spintronics. Realizing noncollinearity in ferrimagnetic insulators is of particular interest as they can be potentially utilized in low-damping spintronics with tunable magnetic order. Within the spinel-ferrite family, Zn and Al-substituted nickel ferrite (NiZAF) has emerged as an excellent choice for low-damping spintronics. However, realizing noncollinearity in such systems remains challenging. Here, we present evidence of noncollinear spin structure in the NiZAF thin films induced by the rare earth Dy-doping, utilizing the soft x-ray spectroscopy methods such as magnetic circular dichroism and x-ray resonant magnetic reflectivity (XRMR). In particular, XRMR reveals a spiral-type spin structure, which is attributed to the Dzyaloshinskii-Moriya interaction, arising due to broken inversion symmetry by the Dy-induced local strain field as confirmed by our theoretical calculations. The realization of noncollinearity in the spinel-ferrite opens pathway to explore the possibility of chiral magnetic domains and topological spin textures exhibiting promise for oxide-based spintronics

The magnetic damping of spin-pumping heterostructures consisting of Pt and Ni 80 Fe 20 (Permalloy, Py) thin films is studied via temperature- and frequency-dependent ferromagnetic resonance (FMR). Additional magnetic and structural characterization is done by transmission electron microscopy (TEM), x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). The frequency-dependence of the FMR linewidth allows to extract the Gilbert damping parameter α as a function of temperature. Py in direct contact with Pt exhibits a strong enhancement of α ( T ) , and the dependence on the thickness of the Py layer suggests this to be an interfacial effect. The enhanced α ( T ) is accompanied by an induced magnetic polarization of the Pt as evidenced by XMCD, while the other magnetic properties of Py as measured with FMR and static magnetometry remain virtually unchanged. The increase of α ( T ) can be efficiently suppressed by the insertion of an Al-spacer layer between Pt and Py as thin as 1 nm, which coincides with the loss of the magnetic polarization of Pt.

The magnetic damping of Ni80Fe20 [Permalloy (Py)] thin films is studied via temperature- and frequencydependent ferromagnetic resonance (FMR) as a function of the Py layer thickness for two different thickness series, Al/Py/sapphire and Al/Py/Al/sapphire, respectively. Additional magnetic and structural characterization is done by superconducting quantum interference device magnetometry as well as x-ray reflectivity and transmission electron microscopy. The frequency dependence of the FMR linewidth allows us to separate the Gilbert-like contributions from non-Gilbert-like ones like two-magnon scattering (TMS) processes. The thickness dependence allows us to separate the derived magnetic parameters such as saturation magnetization Ms, TMS contribution P, and Gilbert damping parameter alpha into their respective bulk and interfacial contributions. While the bulk contribution alpha bulk monotonously decreases with temperature from 0.0061(1) down to 0.0054(1) for both samples series, the interfacial contribution alpha interface shows a subsequent increase at low temperature. This is rather pronounced for the Al/Py/sapphire series, caused by a temperature-dependent TMS contribution. For the Al/Py/Al/sapphire series, the increase at low temperatures is much less pronounced, and a temperatureindependent TMS contribution is only found for the thinnest sample due to a wavy Py film morphology. Correcting for the TMS contributions allows us to extract alpha bulk(T ) which reflects the intrinsic magnetic damping properties of sputtered Py thin films.

Probing the quantum geometry and topology in condensed matter systems has relied heavily on static electronic transport experiments in magnetic fields. Yet, contact-free optical measurements have rarely been explored. Here, we report the observation of resonant magnetic circular dichroism (MCD) in the infrared range in thin film MnBi_{2}Te_{4} exhibiting a spectral intensity that correlates with the anomalous Hall effect. Both phenomena emerge with a field-driven phase transition from an antiferromagnet to a canted ferromagnet. By theoretically relating the MCD to the anomalous Hall effect via Berry curvature for a metallic state, we show that this transition accompanies an abrupt onset of Berry curvature, signaling a topological phase transition from a topological insulator to a doped Chern insulator. Our density functional theory calculation suggests the MCD signal mainly originates from an optical transition at the Brillouin zone edge, hinting at a potential new source of Berry curvature away from the commonly considered Γ point. Our findings demonstrate a novel experimental approach for detecting Berry curvature through spectroscopy of the interband MCD, generally applicable to magnetic materials.

Magnetic domain formation in two-dimensional materials offers insight into the fundamentals of magnetism and serves as a catalyst for the advancement of spintronics. In order to propel these developments, it is crucial to acquire an understanding of the evolution of magnetic ordering at the nanometer scale. In particular, two-dimensional magnetic insulators allow for the realization of atomically sharp magnetoresistive tunneling junctions with nonmagnetic electrodes, therefore lifting one of the major constraints for the realization of computing in memory based on magnetoresistive elements. In this study, we visualize magnetic ordering in monolayers of annite, a fully air-stable layered magnetic mica. Using a nanometer-scale scanning superconducting quantum interference device microscopy, we directly observe domain formation in this representative of two-dimensional magnetic phyllosilicates. Magnetic domain formation in two-dimensional materials is pivotal for advancing spintronics and understanding fundamental magnetism. Here, the authors use scanning superconducting quantum interference device microscopy to visualize magnetic ordering in monolayers of annite, an air-stable phyllosilicate potentially suitable for bio-compatible integration into magnetoresistive tunneling junctions.

Permalloy-based thin films are ferromagnetic materials with excellent magnetic properties, and their detection is appealing for several applications. Here, a Scanning Microwave Microscope is used to characterize a 15 nm film permalloy (Py) layer buried below 5 nm Aluminum (Al). An ad-hoc experimental setup for reduced parasitics and high-sensitivity operation proved to be an excellent platform to probe the sample magnetic response with nanometer spatial resolution. In particular, magneto-impedance effects, i.e. the high-frequency electrical impedance change due to an externally applied magnetic field, have been captured at 11.1 GHz by microwave spectroscopy, and subsequently studied for various magnetic field intensities. The achieved combination of microwave tomography, high-resolution imaging, and magnetic response detection is challenging for other characterization tools; this provides the foundation to characterize modern multilayered and nanostructured magnetic devices with this tool.

The magnetic damping of Ni80Fe20 (Permalloy, Py) thin films is studied via frequency-dependent ferromagnetic resonance (FMR) experiments. The thickness of the Py films is kept constant and they are all protected from oxidation by a 5-nm-thick Al cap layer. To separate the Py film from the oxidic sapphire substrates a systematic variation of the thickness of an additional Al spacer layer was carried out. Py sandwiched in Al exhibits a low, purely Gilbert-like magnetic damping when the Al spacer layer thickness is kept below 3 nm. Above this thickness the magnetic damping is strongly increased because of a pronounced two-magnon contribution. A detailed investigation of the temperature dependence as well as full angular dependence of the FMR allows for correlating the magnetic properties of the Py with the microscopic structural properties of the films as studied by x-ray reflectivity and transmission electron microscopy. It turns out that the detrimental two-magnon processes are activated by an island-like growth of the Al spacer layers, which leads to rough, wavy interfaces with characteristic length scales of the order of ten nanometers. Nevertheless, for Al spacer layers with a thickness below 3 nm, a low, purely Gilbert-like magnetic damping can be observed.

Magnetic damping within Ni80Fe20 (Permalloy, Py) thin films is studied via temperature- and frequency-dependent ferromagnetic resonance (FMR) experiments. While the Py thickness is kept constant at 20 nm, the environment at the film interfaces was systematically varied by fabricating a set of Py thin films grown on widely used substrates and capped with common layers, which are assumed to be suitable to prevent oxidation. The resulting frequency and temperature dependence of the FMR linewidth significantly deviates from the expected Gilbert-like behavior and especially for oxidic interfaces unwanted non-Gilbert-like contributions to the magnetic damping appear, in particular, at low temperatures. In contrast, metallic capping layers avoid non-Gilbert-like contributions. In particular, Py sandwiched in between Al metallic capping and buffer layers exhibits negligible inhomogeneous FMR linewidth broadening and a very small, purely Gilbert-like contribution of alpha = 0.0066(2) down to the lowest temperature.

The interplay between spin-orbit interaction and magnetic order is one of the most active research fields in condensed matter physics and drives the search for materials with novel, and tunable, magnetic and spin properties. Here we report on a variety of unique and unexpected observations in thin multiferroic Ge1-xMnxTe films. The ferrimagnetic order parameter in this ferroelectric semiconductor is found to switch direction under magnetostochastic resonance with current pulses many orders of magnitude lower as for typical spin-orbit torque systems. Upon a switching event, the magnetic order spreads coherently and collectively over macroscopic distances through a correlated spin-glass state. Utilizing these observations, we apply a novel methodology to controllably harness this stochastic magnetization dynamics.

The asymmetry quantification of spin-wave dynamics in confined rectangular permalloy microstrips is suggested and applied to the TR-STXM results and micromagnetic simulations. The excitation was done at a frequency of 9.43GHz using a uniform microwave magnetic field while the external static magnetic field is varied. The results show a higher asymmetry for the double microstrips indicating an influence of an additional microstructure placed in a close proximity to the analyzed structure.

Ni incorporation has been studied in a comprehensive range of Zn/Co-based magnetic oxides to elucidate its valence state and lattice incorporation. The resulting structural and magnetic properties of a range of related types of samples are studied in detail. On the one hand, Ni doping is studied in wurtzite ZnO which is either done by in-diffusion of the Ni into bulk ZnO or by reactive magnetron sputtering for Nidoped thin films of ZnO. The latter is complemented by Ni and Co codoping of ZnO leading to altered magnetic properties which are then dominated by Co. On the other hand, the ZnCo2O4 spinel is codoped with varying amounts of Ni. In the wurtzite oxides, Ni is exclusively found on tetrahedral lattice sites in its formal 2+ oxidation state as deep donor. It behaves as an anisotropic paramagnet, and a limited solubility of Ni below 10% is found. Furthermore, the partial compensation of the antiferromagnetically coupled Co magnetic moments is induced by the Ni due to its smaller magnetic moment. In the ZnCo2O4 spinel, Ni is found to be incorporated in its formal 3+ oxidation state on octahedral sites and also couples antiferromagnetically to the Co moments. At low Ni concentrations, this leads to a lifting of the partial magnetic compensation of the antiferromagnetic ZnCo2O4 spinel and to ferrimagnetism at higher Ni concentrations. Increasing the Ni concentration even further leads to phase separation of cubic NiO resulting in a structurally less defined, exchange-biased composite magnetic oxide.

We present a statistically motivated method to extract magnonic contrast from STXM-FMR measurement with microwave frequencies of the order of \unit[10]{GHz}. With this method it is possible to generate phase and amplitude profiles with a spatial resolution of about \unit[30]{nm} given by the STXM resolution, furthermore this method allows fo a rigoros transformation to reciprocal \vec{k}-space, revealing \vec{k}-dependent magnon properties.

Zinc ferrite (ZnFe2O4) epitaxial thin films were grown by reactive magnetron sputtering on MgAl2O4 and Al2O3 substrates varying a range of preparation parameters. The resulting structural and magnetic properties were investigated using a range of experimental techniques confirming epitaxial growth of ZnFe2O4 with the nominal stoichiometric composition and long-range magnetic order at and above room temperature. The main preparation parameter influencing the temperature Tf of the bifurcation between M(T) curves under field-cooled and zero-field-cooled conditions was found to be the growth rate of the films, while growth temperature or the Ar:O2 ratio did not systematically influence Tf. Furthermore Tf was found to be systematically higher for MgAl2O4 as substrate and Tf extends to above room temperature. While in some samples Tf seems to be more likely correlated with superparamagnetism, the highest Tf occurs in ZnFe2O4 epitaxial films where experimental signatures of magnetic glassiness can be found. Element-selective x-ray magnetic circular dichroism measure-ments aim at associating the magnetic glassiness with the occurrence of a different valence state and lattice site incorporation of Fe pointing to a complex interplay of various competing magnetic interactions in ZnFe2O4.

Spin pumping from a metallic ferromagnet (FM) into an insulating antiferromagnet has been studied across the magnetic phase transition by means of temperature-dependent, broad-band ferromagnetic resonance (FMR) experiments. A set of spin pumping heterostructures consisting of Permalloy (Ni80Fe20) as FM and Zn 1−x Co x O with x=0.3,0.5 and 0.6 (Co:ZnO) as partially compensated antiferromagnetic insulator has been used for which previous experiments have already pointed out the possibility of the existence of spin-pumping. The present experiments allow to reliably separate the various contributions of the temperature-dependent Gilbert damping parameter to the FMR line-width. A careful analysis of the obtained data demonstrates a significant increase of the temperature-dependence of the Gilbert damping parameter α(T) around the magnetic phase transition of Co:ZnO which extends up to room temperature, confirming spin pumping into the fluctuating spin sink of an antiferromagnetic/paramagnetic insulator.

Zinc ferrite (ZnFe_2O_4) epitaxial thin films were grown by reactive magnetron sputtering on MgAl_2O_4 and Al_2O_3 substrates varying a range of preparation parameters. The resulting structural and magnetic properties were investigated using a range of experimental techniques confirming epitaxial growth of ZnFe_2O_4 with the nominal stoichiometric composition and long range magnetic order at and above room temperature. The main preparation parameter influencing the temperature T_f of the bifurcation between M(T) curves under field cooled and zero-field cooled conditions was found to be the growth rate of the films, while growth temperature or the Ar:O_2 ratio did not systematically influence T_f. Furthermore T_f was found to be systematically higher for MgAl_2O_4 as substrate and T_f extends to above room temperature. While in some samples T_f seems to be more likely correlated with superparamagentism, the highest T_f occurs in ZnFe_2O_4 epitaxial films where experimental signatures of magnetic glassiness can be found. Element-selective X-ray magnetic circular dichroism measurements aim at associating the magnetic glassiness with the occurrence of a different valence state and lattice site incorporation of Fe pointing to a complex interplay of various competing magnetic interactions in ZnFe_2O_4.

The asymmetry of spin-wave patterns in confined rectangular Ni$_{80}$Fe$_{20}$ microstrips, both in single and double-strip geometries, is quantified. The results of TR-STXM and micromagnetic simulations are compared. For the TR-STXM measurements and the corresponding simulations the excitation was a uniform microwave field with a fixed frequency of 9.43 GHz, while the external static magnetic field was swept. In the easy axis orientation of the analyzed microstrip, the results show a higher asymmetry for the double microstrip design, indicating an influence of the additional microstrip placed in close proximity to the analyzed one.

Europium sulfide (EuS) thin films are appealing as ferromagnetic semiconductors and luminescent and optomagnetic materials owing to their unique functional properties. With the emerging field of spintronics and magneto-optical devices, chemical vapor deposition (CVD) offers a versatile platform to tune the material properties and the method to fabricate device structures needed for such applications. Herein, we report the growth of high-quality cubic EuS via a versatile CVD process where the new Eu(III) precursors employed facilitate the formation of the target EuS layers under moderated process conditions. Based on the prior evaluation of the physicochemical properties of these precursors using thermal analysis and density functional theory studies, adequate volatility, thermal stability, and sufficient reactivity toward potential co-reactants, namely, elemental sulfur, could be inferred. Thus, the use of toxic hydrogen sulfide generally needed for sulfide film depositions could be avoided, which is a significant advantage in terms of simplifying the deposition process. The as-deposited thin films were analyzed in terms of the structure, composition, and morphology, revealing highly oriented polycrystalline and stoichiometric EuS films. UV/vis measurements yielded a band gap of around 1.6 eV, and Raman spectroscopy exhibited a coupling between the phonons and electron spin systems of EuS. These findings, together with the soft ferromagnetic character of the films derived from semiconducting quantum interference device measurements, signify the potential of CVD-grown EuS for future technological applications.

A reentrant temperature dependence of the thermoresistivity ρxx(T) between an onset local superconducting ordering temperature Tloconset and a global superconducting transition at T=Tglooffset has been reported in disordered conventional 3-dimensional (3D) superconductors. The disorder of these superconductors is a result of either an extrinsic granularity due to grain boundaries, or of an intrinsic granularity ascribable to the electronic disorder originating from impurity dopants. Here, the effects of Fe doping on the electronic properties of sputtered NbN layers with a nominal thickness of 100 nm are studied by means of low-T/high-μ0H magnetotransport measurements. The doping of NbN is achieved via implantation of 35 keV Fe ions. In the as-grown NbN films, a local onset of superconductivity at Tloconset=15.72K is found, while the global superconducting ordering is achieved at Tglooffset=15.05K, with a normal state resistivity ρxx=22μΩ·cm. Moreover, upon Fe doping of NbN, ρxx=40μΩ·cm is estimated, while Tloconset and Tglooffset are measured to be 15.1 K and 13.5 K, respectively. In Fe:NbN, the intrinsic granularity leads to the emergence of a bosonic insulator state and the normal-metal-to-superconductor transition is accompanied by six different electronic phases characterized by a N-shaped T dependence of ρxx(T). The bosonic insulator state in a s-wave conventional superconductor doped with dilute magnetic impurities is predicted to represent a workbench for emergent phenomena, such as gapless superconductivity, triplet Cooper pairings and topological odd frequency superconductivity.

Pyrite-type cobalt disulfide (CoS2), which is one among other stable cobalt sulfide phases, exhibits interesting electronic and magnetic properties. Herein, we demonstrate a tailored metalorganic chemical vapor deposition (MOCVD) pathway for the growth of high-quality ferromagnetic CoS2 thin films. The influence of CVD process parameters on growth and quality of the films was investigated by complementary analyses. Superconducting quantum interference device (SQUID) measurements confirmed the existence of pure CoS2 with a magnetic moment of 0.85 mu(B) and a Curie temperature of 128(5) K. Our findings could pave the way for large-area CoS2 to be used for different technological applications.

We present the element-specific and time resolved visualization of uniform ferromagnetic resonance excitations of a Permalloy (Py) disk-Cobalt (Co) stripe bilayer microstructure. The transverse high frequency component of the resonantly excited magnetization is sampled in the ps regime by a combination of ferromagnetic resonance (FMR) and scanning transmission X-ray microscopy (STXM-FMR) recording snapshots of the local magnetization precession of Py and Co with nanometer spatial resolution. The approach allows us to individually image the resonant dynamic response of each element, and we find that angular momentum is transferred from the Py disk to the Co stripe and vice versa at their respective resonances. The integral (cavity) FMR spectrum of our sample shows an unexpected additional third resonance. This resonance is observed in the STXM-FMR experiments as well. Our microscopic findings suggest that it is governed by magnetic exchange between Py and Co, showing for the Co stripe a difference in relative phase of the magnetization due to stray field influence.