Soft x-ray resonant magneto-optical Kerr effect as a depth-sensitive probe of magnetic heterogeneity: Its application to resolve helical spin structures using linear p polarization

We have calculated the soft x-ray resonant Kerr intensities as a function of the incident grazing angle of linearly p-polarized waves from the model spin structures, where the chirality (handedness) of the spin spirals (twist in depth) in a magnetic layer and the periodicity of a unit spiral are designed to vary. Variations in the chirality and the periodicity lead to noticeable changes in the Kerr intensity versus the grazing angle, which is due not only to a large sensitivity of the Kerr intensity of the linear p polarization to both the magnitude and direction of the transverse components of magnetizations, but also to a large dependence of the depth sensitivity on the grazing angle at the resonance regions. The measurement and analysis of the specular Kerr intensity are relatively straightforward in determining the inhomogeneous spin structures in depth, compared to those of the Kerr rotation and ellipticity. This is proven to be a convenient and useful probe to determine the handedness of spin spiral structures, as well as to resolve the detailed magnetic heterostructures in depth in ultrathin-layered films.open4

Atomic-scale depth selectivity of soft x-ray resonant Kerr effect

A study was performed to demonstrate that soft x-ray Kerr rotation, ??K, versus incident grazing angle, ??, and energy, hv, measurements provide an extremely large depth selectivity on the atomic scales even in an ultrathin single layer, simply by choosing appropriate ?? and hv around the resonant regions. Both the experimental and simulation results of ?? vs ??K measurements were considered for depth-varying magnetization reversals in a 3.5-nm-thick Co layer of NiFe/FeMn/Co/Pd films.open161

Soft x-ray resonant magneto-optical Kerr effect as a depth-sensitive probe of magnetic heterogeneity: A simulation approach

We report a noticeable depth sensitivity of soft x-ray resonant magneto-optical Kerr effect able to resolve depth-varying magnetic heterostructures in ultrathin multilayer films. For various models of depth-varying magnetization orientations in an ultrathin Co layer of realistic complex layered structures, we have calculated the Kerr rotation, ellipticity, intensity spectra versus grazing incidence angle ??, and their hysteresis loops at different values of ?? for various photon energies ?? 's near the Co resonance regions. It is found from the simulation results that the Kerr effect has a much improved depth sensitivity and that its sensitivity varies remarkably with ?? and ?? in the vicinity of the resonance regions. These properties originate from a rich variety of wave interference effects superimposed with noticeable features of the refractive and absorptive optical effects near the resonance regions. Consequently, these allow us to resolve depth-varying magnetizations and their reversals varying with depth in a single magnetic layer and allow us to distinguish interface magnetism from the bulk properties in multilayer films. In this paper, the depth sensitivity of the Kerr effect with an atomic-scale resolution is demonstrated and discussed in details in several manners with the help of model simulations for various depth-varying spin configurations.open9

Interface properties and built-in potential profile of a LaCr O3/SrTi O3 superlattice determined by standing-wave excited photoemission spectroscopy

LaCrO3(LCO)/SrTiO3(STO) heterojunctions are intriguing due to a polar discontinuity along [001], exhibiting two distinct and controllable charged interface structures [(LaO)+/(TiO2)0 and (SrO)0/(CrO2)-] with induced polarization, and a resulting depth-dependent potential. In this study, we have used soft- and hard-x-ray standing-wave excited photoemission spectroscopy (SW-XPS) to quantitatively determine the elemental depth profile, interface properties, and depth distribution of the polarization-induced built-in potentials. We observe an alternating charged interface configuration: a positively charged (LaO)+/(TiO2)0 intermediate layer at the LCOtop/STObottom interface and a negatively charged (SrO)0/(CrO2)- intermediate layer at the STOtop/LCObottom interface. Using core-level SW data, we have determined the depth distribution of species, including through the interfaces, and these results are in excellent agreement with scanning transmission electron microscopy and electron energy-loss spectroscopy mapping of local structure and composition. SW-XPS also enabled deconvolution of the LCO and STO contributions to the valence-band (VB) spectra. Using a two-step analytical approach involving first SW-induced core-level binding-energy shifts and then VB modeling, the variation in potential across the complete superlattice is determined in detail. This potential is in excellent agreement with density functional theory models, confirming this method as a generally useful tool for interface studies

Depth-resolved resonant inelastic x-ray scattering at a superconductor/half-metallic-ferromagnet interface through standing wave excitation

We demonstrate that combining standing wave (SW) excitation with resonant inelastic x-ray scattering (RIXS) can lead to depth resolution and interface sensitivity for studying orbital and magnetic excitations in correlated oxide heterostructures. SW-RIXS has been applied to multilayer heterostructures consisting of a superconductor La1.85Sr0.15CuO4 (LSCO) and a half-metallic ferromagnet La0.67Sr0.33MnO3 (LSMO). Easily observable SW effects on the RIXS excitations were found in these LSCO/LSMO multilayers. In addition, we observe different depth distribution of the RIXS excitations. The magnetic excitations are found to arise from the LSCO/LSMO interfaces, and there is also a suggestion that one of the dd excitations comes from the interfaces. SW-RIXS measurements of correlated-oxide and other multilayer heterostructures should provide unique layer-resolved insights concerning their orbital and magnetic excitations, as well as a challenge for RIXS theory to specifically deal with interface effects

Water Uptake and Proton Conductivity in Porous Block Copolymer Electrolyte Membranes

We demonstrate that the water uptake and conductivity of proton-conducting block copolymer electrolyte membranes can be controlled systematically by the introduction of pores in the conducting domains. We start with a membrane comprising a mixture of homopolymer polystyrene (hPS) and a polystyrene-b-polyethylene-b-polystyrene (SES) copolymer. Rinsing the membranes in tetrahydrofuran and methanol results in the dissolution of hPS, leaving behind a porous membrane. The polystyrene domains in the porous SES membranes are then sulfonated to give a porous membrane with hydrophilic and hydrophobic domains. The porosity is controlled by controlling Φv, the volume fraction of hPS in the blended membrane. The morphology of the membranes before and after sulfonation was studied by scanning transmission electron microscopy (STEM), electron tomography, and resonance soft X-ray scattering (RSoXS). The porous structures before and after sulfonation are qualitatively different. Water uptake of the sulfonated membranes increased with increasing Φv. Proton conductivity is a nonmonotonic function of Φv with a maximum at Φv = 0.1. The introduction of microscopic pores in the conducting domain provides an additional handle for tuning water uptake and ion transport in proton-conducting membranes. (Graph Presented)

Anisotropic short-range structure of Co0.16Pd0.84 alloy films having perpendicular magnetic anisotropy

Polarized Co K edge extended x-ray absorption fine structure measurements obtained with electric vector parallel and perpendicular to the film plane indicate differences in Co bonding along these two directions in room-temperature evaporated Co0.16Pd0.84 alloy films. A local modulation of the Co fraction whose amplitudes are 0.05-0.09 exists along the growth direction in the alloy films. Pd underlayer and Pd spacer layers alternated with the alloy layer induce coherency strains resulting in an anisotropic effective strain state, Both anisotropic strain and local compositional modulation are likely to contribute to the perpendicular magnetic anisotropy observed in these alloys. (C) 1997 American Institute of Physics.open1113sciescopu

Comparison of atomic structure anisotropy between Co-Pd alloys and Co/Pd multilayer films

We have employed Co K-edge extended x-ray absorption fine structure measurements with linear polarization dependence to investigate the chemical short-range order (SRO) and interatomic distance anisotropy in CoxPd1-x alloy (X = 0.16, 0.31) and [Co(2 Angstrom)/Pd(Y Angstrom)](13) multilayer films (Y = 15, 32). The SRO parameters of in-plane first nearest neighbors, 0.063-0.068 in the alloys and 0.012-0.036 in the multilayers, are observed. Surprisingly, these counterintuitive results show clear evidence that the Co atoms at the Co/Pd interfaces in multilayers have more alloylike characteristic than those in alloys with respect to local chemical environment.open1118sciescopu

Temperature-driven growth of antiferromagnetic domains in thin-film FeRh.

The evolution of the antiferromagnetic phase across the temperature-driven ferromagnetic (FM) to antiferromagnetic (AF) phase transition in epitaxial FeRh thin films was studied by x-ray magnetic linear and circular dichroism (XMLD and XMCD) and photoemission electron microscopy. By comparing XMLD and XMCD images recorded at the same temperature, the AF phase was identified, its structure directly imaged, and its evolution studied across the transition. A quantitative analysis of the correlation length of the images shows differences between the characteristic length scale of the two phases with the AF phase having a finer feature size. The asymmetry of the transition from FM to AF upon cooling and AF-FM upon heating is evidenced: upon cooling the formation of AF phase is dominated by nucleation at defects, with little subsequent growth, resulting in a small and non-random final AF domain structure, while upon heating, heterogeneous nucleation at different sites followed by significant domain size growth of the FM phase is observed, resulting in a non-reproducible final FM large domain structure