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The spectroscopy using synchrotron radiation is the advanced tool for materials characterization. In the current work we are reporting recent activity in this research field implemented at the 04BM (PEEM/XAS) beamline of the National Synchrotron Radiation Centre SOLARIS in Krakow, Poland. The beamline is designed to cover wide energy range of soft X-rays, which is well suited for a broad range of applications, including surface physics, material science and magnetism. The comparison of the experimental parameters and selected examples of the results achieved on the PEEM and XAS end stations is demonstrated.

We analyzed the formation of biphase superstructures on the (111)-oriented epitaxial magnetite films on Pt(111) as a function of controlled film stoichiometry. The stoichiometry of the films severa...

We show that in-plane to out-of-plane magnetization switching of a ferromagnetic layer can be driven by antiferromagnetic–ferromagnetic phase transition in a nearby FeRh system. For FeRh/Au/FeAu trilayers, the impact of the magnetic phase transition of FeRh onto the perpendicular magnetization of monoatomic FeAu superlattices is transferred across the Au spacer layer via interlayer magnetic coupling. The polar spin reorientation process of the FeAu spins driven by the magnetic phase transition in the FeRh reveals its major features; namely it is reversible and displays hysteresis.

The common approach to modify the thermoelectric activity of oxides is based on the concept of selective metal substitution. Herein, we demonstrate an alternative approach based on the formation of multiphase composites, at which the individual components have distinctions in the electric and thermal conductivities. The proof-of-concept includes the formation of multiphase composites between well-defined thermoelectric Co-based oxides: Ni, Fe co-substituted perovskite, LaCo0.8Ni0.1Fe0.1O3 (LCO), and misfit layered Ca3Co4O9. The interfacial chemical and electrical properties of composites are probed with the means of SEM, PEEM/XAS, and XPS tools, as well as the magnetic susceptibility measurements. The thermoelectric power of the multiphase composites is evaluated by the dimensionless figure of merit, ZT, calculated from the independently measured electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (λ). It has been demonstrated that the magnitude’s electric and thermal conductivities depend more significantly on the composite interfaces than the Seebeck coefficient values. As a result, the highest thermoelectric activity is observed at the composite richer on the perovskite (i.e., ZT = 0.34 at 298 K).

Silver is one of the most promising cathode materials for low temperature (300–500 °C) solid oxide fuel cells. The most important disadvantage of silver is its migration in the electric field. For better understanding of this phenomenon, an in situ observation of the migration mechanism was undertaken with the use of high-temperature microscopes. Scandia stabilised ceria doped zirconia CeScSZ electrolyte prepared from commercial powder was examined before and after silver migration experiments using scanning electron microscope. X-ray diffraction, broadband electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. The silver electrodes for solid oxide fuel cells were prepared using magnetron sputtering. The described cells under polarisation were examined using a high-temperature low energy electron microscope. Reference cells and post-mortem cells were observed using a scanning electron microscope equipped with high temperature stage. Under polarisation, silver moved inside the electrolyte and along the surface towards the region between electrodes. The structures thus formed were similar to those previously described in the literature; however, direct observation of the deposit growth was unsuccessful. In situ scanning electron microscopy observations of the silver electrode at 650 °C revealed neither melting of the smallest silver particles nor movement of silver structures. Silver migration through the electrolyte caused a reduction in grain interior conductivity of the electrolyte, whereas its grain boundary conductivity remained unaffected.

Systematic studies of the two high-temperature monolayer oxygen structures that exist on the (110) tungsten surface were performed using low-energy electron microscopy and diffraction measurements. Our work questions the commonly accepted interpretation from the literature that striped oxygen superstructures arise from alternating site-exchanged (S-E) domains. We postulate that the superstructures originate from a misfit between tungsten and oxygen lattices while the striped appearance corresponds to a moire pattern. Moreover, we show that the two structures, indicated as 113- and 337-phases due to the characteristic directions of the respective moire patterns, differ considerably in their symmetry properties. This suggests that oxygen atoms in the two overlayers occupy different adsorption sites on average. In particular, the 113-phase features rotational domains that retain mirror symmetries with respect to the [ 001 ] and [ 1 1 ¯ 0 ] directions, whereas the 337-phase is characterized by the appearance of additional domains due to the breaking of these symmetries. We propose structural models for both phases that consistently explain their unusual properties and suggest a universal mechanism for the thermal evolution of oxygen monolayer adsorbed on W(110).

We present studies on CO adsorption on an Fe3O4(1 1 1) surface with a regular tetrahedral termination (Fetet1) and with different hexagonal superstructures called ‘biphase’ structures. All these terminations were precisely controlled on a 70 A magnetite layer epitaxially grown on a Pt(1 1 1) single crystal. The experiments, including low energy electron diffraction, scanning tunnelling microscopy (STM) and temperature-programmed desorption (TPD), were carried out in situ under ultrahigh vacuum conditions. During the TPD measurements, the Fe3O4(1 1 1) surfaces were exposed to 0.1–20 L of CO at 105 K, and then the samples were heated with a linear temperature rise to 600 K. We found that as the Fetet1-terminated area decreases, as confirmed by STM observations, the surface becomes less active in CO adsorption. This means there are fewer adsorption states on the biphase structure than on Fe3O4(1 1 1) with regular termination.

We studied the magnetic properties of 10 and 20 nm-thick, gold-capped FeRh layers grown on MgO(0 0 1). Whereas the majority of the FeRh film undergoes ferromagnetic–antiferromagnetic phase transition upon cooling, a small fraction of the FeRh system remains in the ferromagnetic state at low temperatures. This residual ferromagnetic phase located at the FeRh/MgO interface exhibits perpendicular magnetic anisotropy. Moreover, in the 10 nm-thick film, a small amount of the antiferromagnetic phase survives to high temperatures above the phase transition and probably originates from the epitaxial strains generated at the FeRh/Au interface.

The relation between the interface structure and the exchange bias was studied in the epitaxial CoO/Fe(0 0 1) bilayers that were grown on MgO(0 0 1) using molecular beam epitaxy. Three samples with different interface structures were prepared. The CoO/Fe bilayer, which was prepared using the reactive evaporation of CoO, served as the reference sample. In the other two samples, the CoO/Fe interfaces were modified prior to the CoO growth using either (i) the deposition of a 2 A thick Co layer or (ii) an exposure to molecular oxygen, which resulted in under- and over-oxidized CoO/Fe interfaces, respectively. The actual structures of the resulting interfaces were revealed using conversion electron Mossbauer spectroscopy. For each sample, an iron oxide was found at the interface, and its amount depended on the sample preparation recipe. The exchange bias effect (EB), as a function of the temperature, was experimentally studied in detail using VSM magnetometry. The coercivity showed a distinct peak near the blocking temperature for all samples; however, the peak's location and its width were diverse. The obtained EB values depended on the interface structure. The largest hysteresis loop shift (HEB = 180 Oe at 4 K) was obtained for the sample with the thickest interfacial iron oxide layer.

The thickness- and temperature-induced in-plane spin reorientation transitions (SRT) in epitaxial Fe films on a W(110) single crystal were investigated using X-ray photoemission electron microscopy. We present the real time evolution of the magnetisation switching, and we demonstrate differences between the two transition mechanisms. Whereas both the transitions involve the magnetic domain wall motion, the temperature SRT is additionally accompanied by nucleation of domains. Before and after the thickness-induced SRTs, the sample is in the almost single domain state, which is not the case for the final magnetic configuration after the temperature-induced transition.

We report on in-plane magnetic anisotropy in epitaxial bcc Co/Fe(110) bilayers on W(110). The magnetic surface anisotropy in the Co/Fe(110) bilayers exhibited a strong nonmonotonic dependence on Co coverage. Magneto-optical studies revealed a sharp maximum of the magnetic surface anisotropy, $2.44\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$, at ${d}_{\mathrm{Co}}=5\phantom{\rule{0.16em}{0ex}}\AA{}$. This giant interfacial magnetic anisotropy allowed a small fraction of a Co monolayer to reorient the magnetization of the bulk-like Fe film. We conclude that the mono- and double-layer bcc Co(110) exhibited in-plane magnetic anisotropy with a $[1\overline{1}0]$ easy axis.

We demonstrate that FeRh layers can be implemented to the epitaxial Fe/Au/FeRh spin valve structures grown on MgO(001). Owing to the AFM-FM phase transition in the FeRh film, the magnetic structure of our Fe/Au/FeRh system can be temperature controlled. The indirect exchange coupling between Fe and FeRh films mediated by the Au spacer enables to control the relative orientation of the Fe and FeRh magnetizations by the Au spacer thickness between ferromagnetic and non-collinear with nearly orthogonal magnetizations. Moreover, the evolution of magnetic structure of the Fe/Au/FeRh system along with the AFM-FM transition is accompanied by the reversible in-plane rotation of the top Fe-layer magnetization.We demonstrate that FeRh layers can be implemented to the epitaxial Fe/Au/FeRh spin valve structures grown on MgO(001). Owing to the AFM-FM phase transition in the FeRh film, the magnetic structure of our Fe/Au/FeRh system can be temperature controlled. The indirect exchange coupling between Fe and FeRh films mediated by the Au spacer enables to control the relative orientation of the Fe and FeRh magnetizations by the Au spacer thickness between ferromagnetic and non-collinear with nearly orthogonal magnetizations. Moreover, the evolution of magnetic structure of the Fe/Au/FeRh system along with the AFM-FM transition is accompanied by the reversible in-plane rotation of the top Fe-layer magnetization.

The structural and magnetic properties of ultrathin FeO(111) films on Pt(111) with thicknesses from 1 to 16 monolayers (ML) were studied using the nuclear inelastic scattering (NIS) of synchrotron radiation. Distinct evolution of vibrational characteristics with thickness that is revealed in the phonon density of states (PDOS) witnesses a textbook transition from 2D to 3D lattice dynamics. For the thinnest films of 1 and 2 ML, the low energy part of the PDOS followed a linear dependence in energy that is characteristic for 2-dimensional systems. This dependence gradually transforms with thickness to the bulk ~E-square relation. Density functional theory phonon calculations perfectly reproduced the measured 1 ML PDOS within a simple model of a pseudomorphic FeO/Pt(111) interface. The calculations show that the 2D PDOS character is due to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of the vibrational properties with an increasing thickness is closely related to a transient long range magnetic order and stabilization of an unusual structural phase.

We investigated the spin reorientation transition during the growth of Fe(110) films on W(110) at 250 \ifmmode^\circ\else\textdegree\fi{}C using the in situ nuclear resonant scattering of x rays. The measurements as a function of the grazing incidence angle demonstrated that the spin reorientation proceeds via an intermediate, noncollinear magnetic state, and with increasing thickness, the magnetization reorientation from the [1$\overline{1}$0] to the [001] direction is activated at the film surface and completed at the Fe/W interface. Furthermore, as the temperature was decreased from 250 \ifmmode^\circ\else\textdegree\fi{}C to 160 \ifmmode^\circ\else\textdegree\fi{}C, the temperature-driven spin reorientation transition (SRT) between the [001] and [1$\overline{1}$0] directions was observed with a similar noncollinear transient magnetic state. The thickness-temperature SRT phase diagram was schematically drawn.

FeAu superlattices were grown using MBE by alternative deposition of Fe(0 0 1) and Au(0 0 1) atomic layers. Polar MOKE loops taken at the room temperature showed that all superlattices with single Fe monolayers (MLs) were magnetized along the film normal but the character of the hysteresis loop depended strongly on the repetition number N in a (Fe 1 Au 1 ) N stack, where Fe 1 Au 1 denotes a single sequence of the Fe(0 0 1) and Au(0 0 1) MLs. The loop character changed from a low remanence one for N =20 to a narrow ( H C =50 Oe) rectangular one for N =3. (Fe 1 Au 1 ) 3 stacks, denoted as (FeAu) 3 , were used to construct multilayers, in which they were spaced by K Au(0 0 1) atomic layers (AL). In the tri-layer , (Fe 1 Au 1 ) 3 /Au( d Au )/(Fe 1 Au 1 ) 3 , antiferromagnetic exchange coupling was clearly observed around the Au(0 0 1) spacer thickness d Au =10 AL (about 2 nm). For [(Fe 1 Au 1 ) 3 /Au ( d Au )]× M ( M =4,6) the magnetization process becomes more complicated revealing a sharp multistage spin-flip transition including well-distinguished surface spin flip.

We have investigated the magnetic structure and coupling in epitaxial [Fe3/Au(0 0 1)N/(Fe1Au1)3/Au(0 0 1)N]×2 multilayers. Our system contains alternating (Fe1Au1)3 monoatomic stacks with perpendicular magnetic anisotropy and 3 atomic layer (AL) thick Fe films (Fe3) with an in-plane easy magnetization axis, separated by an Au(0 0 1) spacer layer. Giant magnetoresistance and magnetization measurements as a function of N=4, 5, …, 24 AL of the Au spacer revealed different non-collinear magnetic alignment of the sub-layer magnetization, dependent on the interlayer exchange coupling.

Ultrathin (111)-oriented polar iron oxide films were grown on a Pt(111) single crystal either by the reactive deposition of iron or oxidation of metallic iron monolayers. These films were characterized using low energy electron diffraction, scanning tunneling microscopy and conversion electron Mossbauer spectroscopy. The reactive deposition of Fe led to the island growth of Fe3O4, in which the electronic and magnetic properties of the bulk material were modulated by superparamagnetic size effects for thicknesses below 2 nm, revealing specific surface and interface features. In contrast, the oxide films with FeO stoichiometry, which could be stabilized as thick as 4 nm under special preparation conditions, had electronic and magnetic properties that were very different from their bulk counterpart, w\"ustite. Unusual long range magnetic order appeared at room temperature for thicknesses between three and ten monolayers, the appearance of which requires severe structural modification from the rock-salt structure., Comment: 17 pages, 6 figures, 50 references

The magnetic properties of ultrathin Fe films grown on Au(001) were studied at room temperature as a function of iron thickness in the range of two to three Fe monolayers (ML). The magneto-optic Kerr effect (MOKE) indicated that a spin reorientation from an in-plane direction to the film normal direction takes place when the iron thickness is reduced from 2.3 to 2.0 ML. Values of the effective magnetic anisotropy constants were determined from MOKE and superconducting quantum interference device measurements. The flow analysis of the effective anisotropy constants in anisotropy space revealed that the transition occurs via an intermediate state of canted magnetization.

We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4 A to 14 A. For the iron deposited at 140 K, we obtained perpendicular magnetization at room temperature below the critical thickness of tc = (9 ± 1) A. In the vicinity of tc, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to tc.

We studied the formation of alloys and compounds of the Eu-Fe binary system, in the form of thin films, prepared using molecular beam epitaxy. Diffraction and photoelectron spectroscopy investigations revealed mixing of the elements during the annealing at relatively low temperature. Magnetic studies showed ferromagnetic behavior up to 400 K, and strong thermomagnetic effects and exchange bias indicating the presence of an antiferromagnetic phase and superparamagnetic particles. X-ray photoemission microscopy with dichroic contrast confirmed this hypothesis, showing two types of Eu-Fe alloys with various stoichiometries and showing ferromagnetically ordered particles of 100–500 nm in size. Ferromagnetic particles contain divalent Eu atoms, whereas the antiferromagnetic alloy is probably composed of the trivalent Eu atoms detected in the photoelectron spectra.

Polar Kerr Microscopy was used to visualize characteristic transitions and external magnetic field driven domain structure evolution in a perpendicularly magnetized Fe–Au AF/FM double multilayer structure. Real time imaging performed in the external magnetic field allowed for identification of all sublayers magnetization reversal in accordance with measured PMOKE magnetization curve, showing strong dependence of transition character on the interlayer coupling type and adjacent sublayers magnetization orientation.

Epitaxial FeAl superlattices were used as nonmagnetic spacers in MgO(0 0 1)Fe/FeAl/Fe trilayers. The magnetic hyperfine field at the nuclei of a 57 Fe probe layer, situated in the center of the FeAl spacers, being a measure of the spin polarization from the ferromagnetic Fe layers, was investigated as a function of the total spacer thickness d . A decaying oscillatory dependence of the polarization effect vs. d was found. Magnetization measurements revealed the existence of a temperature dependent 90° coupling. Finally, the correlation of the spin polarization and coupling behavior was clearly identified.