Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between ${\mathrm{SrTiO}}_{3}$ and two insulating polar oxides, ${\mathrm{BiMnO}}_{3}$ and ${\mathrm{LaAlO}}_{3}$. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic ${\mathrm{Ti}}^{3+}$ ions at the interface itself for ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ and to ${\mathrm{Mn}}^{3+}$ ions in the overlayer for ${\mathrm{BiMnO}}_{3}/{\mathrm{SrTiO}}_{3}$. In ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.
Using x-ray absorption spectromicroscopy we have imaged the uncompensated spins induced at the surface of antiferromagnetic (AFM) NiO(100) by deposition of ferromagnetic (FM) Co. These spins align parallel to the AFM spins in NiO(100) and align the FM spins in Co. The uncompensated interfacial spins arise from an ultrathin CoNiOx layer that is formed upon Co deposition through reduction of the NiO surface. The interfacial Ni spins are discussed in terms of the "uncompensated spins" at AFM/FM interfaces long held responsible for coercivity increases and exchange bias. We find a direct correlation between their number and the size of the coercivity.
Zwischgold is a gold-silver bi-layer foil that was popular in medieval European sculptures yet is poorly documented in both historical and modern literature. It is notoriously difficult to identify unambiguously and to study in detail due to its ultra-thinness and tendency to corrode. This article focuses on understanding the corrosion states and technological features of medieval Zwischgold. High-resolution scanning electron microscopy/energy-dispersive X-ray analysis was conducted on 72 Zwischgold samples taken from 47 objects, prepared with ultra-microtomy to investigate the foil structures, layer thickness, elemental composition and corrosion products. Supporting data was obtained through FTIR and Raman spectroscopy regarding the surrounding materials, especially the binding media and pigments. This article aims to fill the knowledge
gap in the history of medieval gilding technology and to provide a scientific basis for future conservation and restoration of Zwischgold artefacts in strongly corroded states.
We show that double-resonance spectra recorded during the simultaneous absorption of x-ray and microwave (MW) photons are a fingerprint of the perturbed electronic configuration of atomic species driven to ferromagnetic resonance. X-ray absorption measurements performed as a function of x-ray energy and polarization over the $\text{Fe}\text{ }{L}_{2,3}$ edges of single-crystal yttrium-iron garnet reveal MW-induced multiplet features related to angular momentum transfer from the MW field to localized $\text{Fe}\text{ }3d$ magnetic sublevels. $\text{O}\text{ }K$-edge absorption spectra demonstrate the formation of dynamic $2p$-orbital magnetization components at O sites coupled to the Fe magnetic moments at tetrahedral and octahedral sites. These results are compared with double-resonance x-ray absorption spectra of Permalloy, showing that the MW transition probability is distributed according to the hybridization character of the $3d$ states and proportional to the unperturbed unoccupied magnetic density of states of metals and insulators.
By direct imaging we determine spin structure changes in Permalloy wires and disks due to spin transfer torque as well as the critical current densities for different domain wall types. Periodic domain wall transformations from transverse to vortex walls and vice versa are observed, and the transformation mechanism occurs by vortex core displacement perpendicular to the wire. The results imply that the nonadiabaticity parameter beta does not equal the damping alpha, in agreement with recent theoretical predictions. The vortex core motion perpendicular to the current is further studied in disks revealing that the displacement in opposite directions can be attributed to different polarities of the vortex core.
The molecular self-assembly and the magnetic properties of two cyclooctatetraenide (COT) - based single-ion magnets (SIM) adsorbed on Ag(100) in the sub-monolayer range are reported. Our study combines scanning-tunneling microscopy, X-ray photoemission spectroscopy and polarized X-ray absorption spectroscopy to show that Cp*ErCOT (Cp* = 1,2,3,4,5-pentamethylcyclopentadienide anion) SIMs self-assemble as alternating compact parallel rows including standing-up and lying-down conformations, following the main crystallographic directions of the substrate. Conversely, K[Er(COT)$_2$], obtained from subliming the [K(18-c-6)][Er(COT)$_2$]$\cdot$ 2THF salt, forms uniaxially ordered domains with the (COT)$^{2-}$ rings perpendicular to the substrate plane. The polarization-dependent X-ray absorption spectra reproduced by the multiX simulations suggest that the strong in-plane magnetic anisotropy of K[Er(COT)$_2$]/Ag(100) and the weak out-of-plane anisotropy of Cp*ErCOT/Ag(100) can be attributed to the strikingly different surface ordering of these two complexes. Compared to the bulk phase, surface-supported K[Er(COT)$_2$] exhibits a similarly large hysteresis opening, while the Cp*ErCOT shows a rather small opening. This result reveals that despite structural similarities, the two organometallic SMMs have strongly different magnetic properties when adsorbed on the metal substrate, attributed to the different orientations and the resulting interactions of the ligand rings with the surface.
