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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.

The control of the spin orientation in antiferromagnets is of key importance in modern spintronics. Here, the authors demonstrate controllable antiferromagnetic spin switching in a synthetically fabricated epitaxial ferromagnet/antiferromagnet bilayer. Thanks to the precise nanoengineering of ferromagnet anisotropy and interface exchange coupling, two orthogonal spin states in the antiferromagnet can be either thermally stabilized in a field-free manner or written by a small external magnetic field.

We report on in-plane magnetic anisotropy in Au/Co/Fe(1 1 0) trilayers epitaxially grown on W(1 1 0). We observe single and double in-plane spin reorientation transitions that can be explained by the strongly non-monotonic dependence of magnetic anisotropy on the Co sublayer thickness. We point out the significant flexibility of the Au/Co/Fe(1 1 0) system for switching the in-plane easy axis of the magnetic anisotropy between the [ 1 1 ¯ 0 ] and [0 0 1] directions of the bcc(1 1 0) plane.

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.

We report on exchange bias and interfacial antiferromagnetic spin orientation in epitaxial CoO(111)/Fe(110) bilayers. Our X-ray magnetic linear dichroism and magneto-optic Kerr effect results show that exchange bias sets on in the zero-field-cooled system and is governed by in-plane magnetic state Fe(110) sublayer above Neel temperature of CoO. Uniaxial magnetic anisotropy of Fe layer determines the direction of interfacial frozen antiferromagnetic CoO spins within CoO(111)//Fe(110) sample plane. Choice of the particular magnetic state of Fe sublayer, when passing Neel temperature of CoO, determines both the axis and direction of interfacial antiferromagnetic spins after the sample is cooled and allows for imprinting their +/- 90° and 0/180° alignment within the sample plane.

A ferromagnet/antiferromagnet (FM/AFM) Fe/NiO bilayer was grown using molecular beam epitaxy on MgO(001) and Cr buffered MgO(001) substrates. X-ray linear dichroism measurements showed a dominating out-of-plane component for the NiO spins in Fe/NiO/MgO and an in-plane spin direction for NiO layers grown on the Cr buffer. Furthermore, systematic studies on the magnetic properties of Fe/NiO grown on the wedge-shaped Cr buffer revealed a continuous strain-induced spin reorientation transition from out-of-plane to in-plane NiO spin directions when the Cr thickness increased from 0 nm to 3.5 nm. The analysis of the in-plane magnetic structure of NiO in Fe/NiO/Cr showed a pronounced uniaxial anisotropy in thin AFM layers. The AFM spins are perpendicular to the Fe spins due to spin–flop interaction. These results demonstrate the feasibility of using strain and coupling with FMs to manipulate spin structures in NiO.

We report on the large coercivity enhancement in epitaxial Fe/FeRh bilayer grown on W(110). It is shown that the coercive field increases by almost an order of magnitude when the FeRh alloy undergoes a phase transition from the ferromagnetic to antiferromagnetic state. Analysis of temperature spin structure evolution of the FeRh alloy across the magnetic transition reveals that the observed coercivity enhancement is caused by the interfacial spin-flop coupling between Fe and the antiferromagnetic FeRh layer.

We report on the in-plane magnetic anisotropy in Au/Fe(1 1 0) and Co/Au/Fe(1 1 0) bi- and trilayers epitaxially grown on a W(1 1 0) single crystal. Magnetic surface anisotropy (MSA) exhibits a strongly non-monotonic, oscillatory behavior as a function of Au thickness. In the case of the Au/Fe(1 1 0) bilayers bi-periodic oscillations were observed and interpreted in terms of quantum well states that are affected by the alternating complete and in-complete atomic layers of Au. Thin bcc Co films grown on Au/Fe(1 1 0) bilayers strongly enhance MSA and for the Co/Au/Fe system magnetic anisotropy oscillates as a function of the Au spacer thickness due to the oscillatory interlayer coupling.

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.

We show that in a uniform thickness NiO(111)/Fe(110) epitaxial bilayer system, at given temperature near 300 K, two magnetic states with orthogonal spin orientations can be stabilized in antiferromagnetic NiO. Field-free, reversible switching between these two antiferromagnetic states is demonstrated. The observed phenomena arise from the unique combination of precisely tuned interface magnetic anisotropy, thermal hysteresis of spin reorientation transition and interfacial ferromagnet/antiferromagnet exchange coupling. The possibility of field-free switching between two magnetic states in an antiferromagnet is fundamentally interesting and can lead to new ideas in heat assisted magnetic recording technology.

Antiferromagnet/ferromagnet (AFM/FM) bilayers that display the exchange bias (EB) effect have been subjected to intensive material research, being the key elements of novel spintronics systems. In a commonly accepted picture, the antiferromagnet, considered as a rigid material due to its high anisotropy and magnetic hardness, controls the magnetic properties of the ferromagnet, such as a shift of the hysteresis loop or coercivity. We show that this AFM-FM master-slave hierarchy is not generally valid and that the influence of the ferromagnet on the magnetic anisotropy (MA) of the neighbouring antiferromagnet must be considered. Our computer simulation and experimental studies of EB in an epitaxial CoO/Fe(110) bilayer show that the ferromagnetic layer with strong uniaxial magnetic anisotropy determines the interfacial spin orientations of the neighbouring AFM layer and rotates its easy axis. This effect has a strong feedback on the EB effect experienced by the FM layer. Our results show new physics behind the EB effect, providing a route for grafting a desired anisotropy onto the AFM and for precise tailoring of EB in AFM/FM systems.

In our study, we examined the chemical and magnetic properties of FeO in an epitaxial Fe/MgO(dMgO)/FeO trilayer for different MgO thicknesses, dMgO. Analysis of the chemical structure revealed a stoichiometry improvement in the FeO layer in Fe/MgO/FeO in comparison with a Fe/FeO bilayer. Furthermore, we showed that deposition of a subtle MgO layer at the Fe/FeO interface results in an enhanced exchange interaction between Fe and FeO. For dMgO = 1.4 A, we noted a 200% enhancement in the exchange bias in Fe/MgO/FeO compared to that in Fe/FeO.

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 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.

Metal-oxide ${\mathrm{[Fe}}_{K}/(\text{MgO}){}_{L}{\mathrm{]}}_{N}$ multilayers were grown on MgO(001) substrates for various integer numbers $(K,L)$ of the Fe(001) and MgO(001) monolayers, respectively, and the number of repetitions $N$ varied from 6 to 30. Room-temperature conversion electron M\"ossbauer spectroscopy (CEMS) measurements proved that the magnetic properties of these monoatomic multilayers were extremely sensitive to both the Fe and MgO sublayer thicknesses. A stable ferromagnetic state and a strong perpendicular magnetization component at room temperature were obtained by changing the sublayer thickness and the number of multilayer repetitions. The analysis of the CEMS spectra in correlation with the magneto-optic Kerr effect measurements indicated a complicated domain structure in this special type of metal-insulator material. The vortexlike domain structure was confirmed by micromagnetic simulations.

Exchange bias (EB) is studied in an epitaxial CoO/Fe bilayer grown by molecular beam epitaxy on MgO(001). The characterization of the layer structure and interface quality was performed using LEED, AES and conversion electron Mossbauer spectroscopy(CEMS). Detailed experimental studies of the EB effect as a function of temperature were carried out using the magneto-optical Kerr effect. Notwithstanding the formation of Fe oxides at the CoO/Fe interface, as evidenced by the CEMS measurements, we observed a negative EB with blocking temperature T B = 257 K. At temperatures close to T B , the coercive field reaches a maximum, which is in agreement with the stiles and McMichael model.

Thin ${}^{57}$Fe layers evaporated onto an MgO(100) single-crystal substrate and covered by an evaporated MgO layer were studied by low-temperature conversion electron M\"ossbauer spectroscopy. The temperature dependence of the spectra indicates superparamagnetic behavior below 8 ML nominal thickness of the Fe layer signaling a cluster-type growth mode. The low-temperature hyperfine fields are consistent with a model that defines two types of metallic Fe atoms: bulklike and interfacial ones. Formation of FeO or (Fe,Mg)O at the interface layer is not observed. The sample with a 4-ML Fe layer when grown over a cleaved MgO substrate shows almost perfect perpendicular magnetization, as locally probed at 15 K by the hyperfine magnetic field, while random magnetization orientation and lower blocking temperature is observed in the case of a polished substrate. The perpendicular anisotropy observed at low temperature is attributed to mechanical stresses arising from the epitaxial relation and the different temperature dilatation of the subsequent layers.

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.

An in-plane spin-reorientation transition occurring during the growth of epitaxial Fe films on W(110) was studied in situ by using the nuclear resonant scattering of synchrotron radiation. The spin-reorientation transition originates at the Fe/W(110) interface and proceeds via a noncollinear spin structure resembling a planar domain wall that propagates towards the surface with increasing film thickness.

Comparative studies of the magnetic properties of epitaxial Fe/MgO/Fe trilayers, which were directly grown on an MgO(001) crystal and a homoepitaxial MgO buffer layer, were performed to examine the interlayer exchange coupling as a function of the MgO spacer thickness. Measurements of the magneto-optic Kerr effect at room temperature demonstrated that there was a strong antiferromagnetic coupling (AFC) between the Fe layers, which was mediated by the insulating MgO barrier. A measurable AFC was found in a range of MgO thickness (dMgO) from a single monolayer (2 A) to 6 A, which had a maximum strength of −1.15 ergs/cm2 at dMgO = 2.7 A for the Fe/MgO/Fe trilayers that were prepared on the buffered sample and was notably weaker for the trilayers that were prepared directly on the MgO(001).

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.

Nuclear resonant scattering (NRS) of synchrotron radiation was used to investigate the magnetic anisotropy of iron films in MgO/Fe(t)/MgO(001) structures for t = (4–10) A. The low-temperature NRS spectra were analyzed using a static magnetization model involving two interface-like components and a bulk-like component. We confirmed the existence of perpendicular magnetic anisotropy in MgO/Fe/MgO structures at 10 K with an increasing in-plane component of the magnetization for t > 8 A over the entire thickness of the Fe film. The evolution of the magnetic structure with increasing temperature was studied for an Fe film thickness of 8.8 A, and the temperature dependence of superparamagnetic fluctuations with characteristic frequencies ranging over tens of MHz was interpreted in terms of a spin reorientation transition. We showed that interfacial magnetic moments are less sensitive to thermal excitations than the magnetic moments in the film center, which was attributed to the spin pinning at the interface.

Conversion electron Mossbauer spectroscopy proved in the past to be very useful in studying surface and ultrathin film magnetism with monolayer resolution. Twenty years later, its time-domain analogue, the nuclear resonant scattering (NRS) of synchrotron radiation, showed up to be by orders of magnitude faster and more efficient. The evolution of the spin structure in epitaxial 57Fe films on a tungsten W(110) was studied via the accumulation of the NRS time spectra directly during Fe film deposition. In the 0.5 – 4 monolayers Fe thickness range, the complex non-collinear magnetic structure was derived from the NRS data, resulting from the deviation from the layer by layer growth mode. For thicker Fe films, the in-plane thickness induced spin reorientation transition could be clearly identified. Based on the NRS analysis it is shown that SRT process originates at the Fe/W(110) interface and proceeds through a transient fan-like magnetization structure.