Ferromagnetic order controlled by the magnetic interface of LaNiO3/La2/3Ca1/3MnO3 superlattices.

Interface engineering in complex oxide superlattices is a growing field, enabling manipulation of the exceptional properties of these materials, and also providing access to new phases and emergent physical phenomena. Here we demonstrate how interfacial interactions can induce a complex charge and spin structure in a bulk paramagnetic material. We investigate a superlattice (SLs) consisting of paramagnetic LaNiO3 (LNO) and highly spin-polarized ferromagnetic La2/3Ca1/3MnO3 (LCMO), grown on SrTiO3 (001) substrate. We observed emerging magnetism in LNO through an exchange bias mechanism at the interfaces in X-ray resonant magnetic reflectivity. We find non-symmetric interface induced magnetization profiles in LNO and LCMO which we relate to a periodic complex charge and spin superstructure. High resolution scanning transmission electron microscopy images reveal that the upper and lower interfaces exhibit no significant structural variations. The different long range magnetic order emerging in LNO layers demonstrates the enormous potential of interfacial reconstruction as a tool for tailored electronic properties.

Magnetic proximity effect in YBa2Cu3O7/La(2/3)Ca(1/3)MnO3 and YBa2Cu3O7/LaMnO(3+δ) superlattices.

Using neutron reflectometry and resonant x-ray techniques we studied the magnetic proximity effect (MPE) in superlattices composed of superconducting YBa2Cu3O7 and ferromagnetic-metallic La0.67Ca0.33MnO3 or ferromagnetic-insulating LaMnO(3+δ). We find that the MPE strongly depends on the electronic state of the manganite layers, being pronounced for the ferromagnetic-metallic La0.67Ca0.33MnO3 and almost absent for ferromagnetic-insulating LaMnO(3+δ). We also detail the change of the magnetic depth profile due to the MPE and provide evidence for its intrinsic nature.

History-dependent domain and skyrmion formation in 2D van der Waals magnet Fe3GeTe2.

The discovery of two-dimensional magnets has initiated a new field of research, exploring both fundamental low-dimensional magnetism, and prospective spintronic applications. Recently, observations of magnetic skyrmions in the 2D ferromagnet Fe3GeTe2 (FGT) have been reported, introducing further application possibilities. However, controlling the exhibited magnetic state requires systematic knowledge of the history-dependence of the spin textures, which remains largely unexplored in 2D magnets. In this work, we utilise real-space imaging, and complementary simulations, to determine and explain the thickness-dependent magnetic phase diagrams of an exfoliated FGT flake, revealing a complex, history-dependent emergence of the uniformly magnetised, stripe domain and skyrmion states. The results show that the interplay of the dominant dipolar interaction and strongly temperature dependent out-of-plane anisotropy energy terms enables the selective stabilisation of all three states at zero field, and at a single temperature, while the Dzyaloshinksii-Moriya interaction must be present to realise the observed Néel-type domain walls. The findings open perspectives for 2D devices incorporating topological spin textures.

Pinned orbital moments - A new contribution to magnetic anisotropy.

Reduced dimensionality and symmetry breaking at interfaces lead to unusual local magnetic configurations, such as glassy behavior, frustration or increased anisotropy. The interface between a ferromagnet and an antiferromagnet is such an example for enhanced symmetry breaking. Here we present detailed X-ray magnetic circular dichroism and X-ray resonant magnetic reflectometry investigations on the spectroscopic nature of uncompensated pinned magnetic moments in the antiferromagnetic layer of a typical exchange bias system. Unexpectedly, the pinned moments exhibit nearly pure orbital moment character. This strong orbital pinning mechanism has not been observed so far and is not discussed in literature regarding any theory for local magnetocrystalline anisotropy energies in magnetic systems. To verify this new phenomenon we investigated the effect at different temperatures. We provide a simple model discussing the observed pure orbital moments, based on rotatable spin magnetic moments and pinned orbital moments on the same atom. This unexpected observation leads to a concept for a new type of anisotropy energy.

Magnetic moments induce strong phonon renormalization in FeSi.

The interactions of electronic, spin and lattice degrees of freedom in solids result in complex phase diagrams, new emergent phenomena and technical applications. While electron-phonon coupling is well understood, and interactions between spin and electronic excitations are intensely investigated, only little is known about the dynamic interactions between spin and lattice excitations. Noncentrosymmetric FeSi is known to undergo with increasing temperature a crossover from insulating to metallic behaviour with concomitant magnetic fluctuations, and exhibits strongly temperature-dependent phonon energies. Here we show by detailed inelastic neutron-scattering measurements and ab initio calculations that the phonon renormalization in FeSi is linked to its unconventional magnetic properties. Electronic states mediating conventional electron-phonon coupling are only activated in the presence of strong magnetic fluctuations. Furthermore, phonons entailing strongly varying Fe-Fe distances are damped via dynamic coupling to the temperature-induced magnetic moments, highlighting FeSi as a material with direct spin-phonon coupling and multiple interaction paths.

Hematologic values of conditioned, captive wild coyotes.

Hemograms were performed on blood samples collected from 35 coyotes (Canis latrans). Hematologic values were established for conditioned, captive wild coyotes under controlled conditions of environment and nutrition.

Electrophoretic protein analysis in the conditioned captive wild coyote, Canis latrans.

Total protein, albumin and serum protein values were determined on 19 male and 14 female captive, vaccinated, wild coyotes. Male coyotes had significantly higher total protein, alpha 1 and alpha 2 globulin levels than female coyotes. Captive, wild coyotes had lower values for total protein, albumin and beta globulins, and higher values for alpha 2 and gamma globulins than similar values for laboratory dogs. Albumin values determined by bromcresol green were slightly higher than values derived by electrophoresis. This difference was non-significant.

Magnetic reflectometry of heterostructures.

Measuring the magnetic configuration at complex buried layers and interfaces is an important task, which requires especially a non-destructive probing technique. X-ray resonant magnetic reflectometry (XRMR) combines the non-destructive depth profiling potential of x-ray reflectometry with the excellent sensitivity for magnetic phenomena, utilizing the x-ray magnetic circular dichroism effect. It provides the magnetic spatial distribution with a precision down to the angstrom scale, combined with element and symmetry specificity, sub-monolayer sensitivity, and the possible separation of spin and orbital magnetic moments. This review provides an overview to the XRMR technique in a tutorial way. We focus on the introduction to the theory, measurement types, and data simulation. We provide related experimental examples and show selected applications.

The effect of magnetic anisotropy on the spin configurations of patterned La(0.7)Sr(0.3)MnO3 elements.

We study the effect of magnetocrystalline anisotropy on the magnetic configurations of La0.7Sr0.3MnO3 bar and triangle elements using photoemission electron microscopy imaging. The dominant remanent state is a low energy flux-closure state for both thin (15 nm) and thick (50 nm) elements. The magnetocrystalline anisotropy, which competes with the dipolar energy, causes a strong modification of the spin configuration in the thin elements, depending on the shape, size and orientation of the structures. We investigate the magnetic switching processes and observe in triangular shaped elements a displacement of the vortex core along the easy axis for an external magnetic field applied close to the hard axis, which is well reproduced by micromagnetic simulations.

Note: unique characterization possibilities in the ultra high vacuum scanning transmission x-ray microscope (UHV-STXM) "MAXYMUS" using a rotatable permanent magnetic field up to 0.22 T.

Using the x-ray magnetic circular dichroism effect, the soft x-ray range provides powerful detection capabilities concerning element specific structural, chemical, and magnetic properties. We present the implementation of a variable 0.22 T magnet system based on permanent magnets into the new UHV scanning microscope "MAXYMUS" at HZB/BESSY II, allowing surface sensitive and simultaneous standard transmission microscopic investigations in a variable external magnetic field. The outstanding potential of these new investigation possibilities will be demonstrated showing the development of the magnetic domain structure concurrently at the surface and in the bulk, providing a profound understanding of fundamental mechanisms in coupled magnetic systems.

On the imaging of the flux-line lattice of a type-II superconductor by soft X-ray absorption microscopy.

A new method is proposed for the imaging of the flux-line lattice of a type-II superconductor by soft X-ray absorption microscopy. It is shown that the method is very demanding but probably realisable in the foreseeable future. The new method has the potential to image in real space static and dynamical properties of the flux-line lattice at arbitrary external fields and with single-flux-line resolution.

HoFe - Garnet soft XMCD measurements below and above the compensation temperature.

We have investigated the magnetism of Holmium-Iron-Garnet (Ho3Fe5O12) at the Ho M4,5 - the Fe L2,3 - and the O K - edges. As expected switching of the sub-lattice magnetization is observed at the compensation temperature. We will give detailed analysis ofthe Ho and Fe XMCD signals, using sum rules. Fe dichroism is analyzed in terms of 3d ground state moments and compared to Gadolinium-Iron-Garnet (Gd3Fe5O12). Contributions of octahedral and tetrahedral Fe sites could be separated and analyzed quantitatively. At the oxygen K edge two different structures are observable. Those structures show different temperature dependencies. Therefore we address these features separately to Fe and Rare Earth contributions.

Non-symmetric influences in the total electron yield X-ray magnetic circular dichroism signal in applied magnetic fields.

The total electron yield current is strongly influenced by external magnetic fields. As known before, this side effect can be slightly reduced by applied external bias voltages increasing the total sample drain current nearly up to saturation. Nevertheless those effects are not perfectly reduced in almost all X-ray Magnetic Circular Dichroism (XMCD) applications and are more prominent in very small XMCD signals, like O K edge spectra. We show that asymmetries in the total electron yield field response will result in XMCD offset signals, which are strongly photon energydependent and follow the nonmagnetic absorption signal. A simple but effective method to prevent those offset signals, is the use of asymmetric magnetic fields. A quantitative analysis and a numerical reduction method for those offset signals are shown.

Strong anisotropy of projected 3d moments in epitaxial CrO2 films.

Soft x-ray magnetic circular dichroism (XMCD) spectra have been investigated for different crystallographic projections of CrO2. Strong anisotropic orbital Cr 3d contributions and a change of sign of the XMCD signal is observed and attributed to t(2g) majority states near the Fermi level. Additionally, moment analysis exhibits anisotropic behavior in the projected spin contributions of CrO2 assigned to a strong magnetic dipole term T(z), consistent with an intrinsic magnetic easy axis behavior along the CrO2 [001] axis. A reduced projected isotropic Cr 3d spin moment has been interpreted in terms of hybridization with oxygen.

XMCD study of the Ruddlesden-Popper Phase La1.2Nd0.2Sr1.6Mn2O7.

X-ray Magnetic Circular Dichroism (XMCD) measurements of the Ruddlesden-Popper Phase La1,2Nd0,2Sr1.6Mn2O7 are reported. The Mn K. La and Nd L2,L3 edges have been measured on a powder sample at two different magnetic fields at low temperature. The analysis of the spectra at B = 1T indicates a large orbital moment of the Nd 5d-states and a significant spin-polarization of the La 5d-band. Furthermore at the Mn K-edge a XMCD-signal is observed, showing a polarization of the Mn 4p-band. At lower field (0.2T) all XMCD-signals are about two times smaller corresponding to the lower total magnetization. The signal at the Nd L2 edge vanishes completely at 0.2T.