Absorption Edges Of Cobalt Research Articles

Electronic processes occurring during ultrafast demagnetization of cobalt triggered by x-ray photons tuned to the Co L3 resonance

Magnetization dynamics triggered with ultrashort laser pulses has been attracting significant attention, with strong focus on the dynamics excited by VIS/NIR pulses. Only recently, strong magnetic response in solid materials induced by intense X-ray pulses from free-electron lasers (FELs) has been observed. The exact mechanisms that trigger the X-ray induced demagnetization are not yet fully understood. They are subject of on-going experimental and theoretical investigations. Here, we present a theoretical analysis of electronic processes occurring during demagnetization of Co multilayer system irradiated by X-ray pulses tuned to L$_3$-absorption edge of cobalt. We show that, similarly as in the case of X-ray induced demagnetization at M-edge of Co, electronic processes play a predominant role in the demagnetization until the pulse fluence does not exceed the structural damage threshold. The impact of electronic processes can reasonably well explain the available experimental data, without a need to introduce the mechanism of stimulated elastic forward scattering.

Time-resolved measurements of Ni 80Fe 20/MgO/Co trilayers in the extreme ultraviolet range

Abstract We performed an element-selective magneto-optic characterization of Ni 80Fe 20/MgO/Co magnetic trilayers employing the resonant magnetic reflectivity of extreme ultraviolet (XUV) radiation tuned to the M absorption edges of cobalt (60.2 eV) and nickel (67.5 eV). Static reflectivity shows a large magnetic contrast of up to 80% for the top Co and 20% for the buried Ni 80Fe 20 layers. The magneto-dynamic response of the trilayers to the ultrashort field pulse exhibits oscillations in a frequency range of up to 6.5 GHz associated exclusively with magnetization dynamics of the top Co layer. The presented results demonstrate the feasibility of element-specific magneto-dynamic studies of magnetic multilayers employing resonant XUV reflectivity at the M absorption edges.

Resonant magnetic reflectivity in the extreme ultraviolet spectral range: Interlayer-coupled Co/Si/Ni/Fe multilayer system

A polycrystalline test structure comprising a 5 nm cobalt and a 10 nm nickel/iron layer separated by a silicon layer ranging from 1.5 to 4 nm prepared by thermal evaporation has been investigated by resonant magnetic reflectivity measurements of horizontally polarized light in the extreme ultraviolet spectral range. By exploiting the transversal magneto-optical Kerr effect at the $M$ absorption edges of cobalt and nickel (59.5 eV and 66.5 eV) a magnetic contrast as large as 80% for cobalt and 25% for nickel can be obtained near a Brewster angle of about $45\ifmmode^\circ\else\textdegree\fi{}$. Angle- and energy-dependent scans of the magnetic asymmetry as well as element-selective, magneto-optical loops of the hysteresis were recorded against the thickness of the interlayer, reflecting the switching behavior of the individual ferromagnetic layers as a function of the interlayer coupling.

A scanning x-ray microscope using circularly polarized radiation at the TRISTAN accumulation ring and its application to observation of ferromagnetic domains

A scanning x-ray microscope using circularly polarized radiation has been constructed at the beamline NE1B of the 6.5-GeV TRISTAN accumulation ring (AR). It uses a Fresnel zone plate as an x-ray focusing lens. Its spatial resolution has been evaluated to be ∼1.2 μm at the energy of 933 eV. Depending on the relative orientation between the photon spin and the local magnetization direction, the magnetic domains recorded in a piece of videotape have been successfully observed visually at the L2,3 absorption edges of cobalt. The contrast of the image arises from the magnetic circular dichroism in core-level photoemission of ferromagnets. The observed contrast was certainly reversed between L2 and L3 edges.

X‐ray K absorption studies on some cobalt thiosemicarbazones

AbstractThe x‐ray K absorption edges of Co in some thiosemicarbazones were recorded. The results are discussed qualitatively in terms of molecular symmetry and the nature of the ligand. The extended x‐ray absorption fine structure associated with the K absorption edge of cobalt in these thiosemicarbazones was also studied. The average metalligand bond lengths in these complexes were calculated.

XANES study of two bivalent cobalt polymers

AbstractXANES (x‐ray absorption near edge structure) in the vicinity of the K absorption edge of cobalt has been studied for two bivalent cobalt polymers, viz. cobalt(II) azelaic acid bis(phenylhydrazide) and cobalt(II) sebacic acid bis(2,4‐dinitrophenylhydrazide), using a bent crystal x‐ray spectrograph of the Cauchois type. This study helped in the determination of the average bond lengths in the two compounds. The study of the chemical shifts and the edge widths throws some light on the relative covalency in these complexes.

X‐ray K absorption edges of cobalt and copper in their tetraphenylporphyrin (TPP) and formate di‐ and tetrahydrate (FDH) (FTH) compounds

AbstractK absorption edge data for TPP and FDH compounds of cobalt and copper have been recorded. Edge position shifts, changes in edge widths and shifts in the position of first absorption maximum are discussed.

Study of some cobalt biomolecular complexes by x‐ray absorption spectroscopy

AbstractThe fine structure in the vicinity of the K absorption edge of cobalt in some cobalt biomolecular complexes has been studied using a bent crystal x‐ray spectrograph of the Cauchois type. The average metal—ligand bond length in these complexes has been determined by applying Levy's theory.

X‐Ray K absorption edge studies of cobalt in complexes with nitrogen based aromatic ligands

AbstractThe X‐ray K absorption edges of cobalt in some complexes with nitrogen based ligands [α‐Co(py)2Cl2, Co(py)2Br2, Co(bipy)Br2 and Co(phen)Br2] have been recorded using a 40 cm bent crystal spectrogrph. The absorption edge shift and edge width have been discussed in terms of effective nuclear charge, molecular symmetry and the nature of the ligand. The radii of the first coordination sphere have been calculated using Levy's method and a correlation suggested.

Chemical shifts and fine structure of the cobalt K -absorption edge

We have measured the chemical shifts of the x-ray K -absorption edge of cobalt in the compounds CoF2, CoO, Co2O3, Co(CH3COO)2· 4H2O, CoSO4· 7H2O, CoC2O4· 2H2O, CoCl2· 6H2O, CoBr2, CoS, CoCO3, and Co3(PO4)2 8H2O. The chemical shifts have been found to vary linearly with the product i m2, where i is the ionicity and m the valence. We have also measured the fine structure observed on the high energy side of the edge in the metal and in the first six compounds. The positions of maxima and minima have been compared with theoretical predictions. The first absorption maximum in the metal has been interpreted as a plasma absorption. The bond lengths have been estimated from the fine structure.

X ray K absorption edge of cobalt and some of its compounds

The chemical shift in the X ray K absorption edge of cobalt in a number of its compounds has been measured using a bent crystal spectrograph of Cauchois design employing a thin mica crystal bent to a radius of curvature of 40 cm. Measured values of these shifts have been used to determine the charge on a cobalt atom in these compounds.