A FTIR search for linkage isomerism of CN(-) ions adsorbed on oxides and zeolites.

Adsorption of HCN and DCN was studied at 150-600 K on TiO(2), ZnO, MgO and a set of X zeolites by means of FTIR spectroscopy. At the lowest temperatures adsorption is non-dissociative and occurs on surface OH groups of oxides, cations and coordinately unsaturated oxygen atoms. Bands at 2243-2147 cm(-1) assignable to CN(-) ions start to grow in the spectra of ZnO at 170 K, at 250 K for MgO and at 300 K for TiO(2), where bands of polymeric species appear simultaneously. The structure of bands near 2200 cm(-1) in the spectra of the studied oxides does not display a temperature dependence characteristic of isomeric forms. Reversible temperature changes of the band of CN(-) ions in Na-, K-, Rb- and CsX zeolites exposed to HCN provide evidence for linkage isomerism, when the ions bound to alkali cations via C- or N- atoms co-exist in the thermodynamic equilibrium. C-Bonded species account for the stronger band at 2200-2140 cm(-1), while the low-frequency shoulder of this band, which appears and grows at elevated temperatures, is due to the energetically less favorable N-bonded form. The enthalpy of isomerization, estimated from the temperature dependence of band intensities, decreases from ca 20 kJ mol(-1) or more for Na(+) and K(+) to 7.6 kJ mol(-1) for Cs(+), in accordance with the electrostatic model.

Structural and magnetic behaviour of soft magnetic Finemet-type ribbons.

Different kinds of magnetic anisotropies have been induced during the nanocrystallization process of Co- and Ni-rich amorphous ferromagnetic (Finemet) ribbons by the application of a constant stress or an axial magnetic field during the annealing process. Magnetization measurements have evidenced the presence od macroscopic anisotropy in the treated samples. The main goal of this work has been, after a careful DSC study, the structural analysis of the treated ribbons using X-ray Diffraction and Atomic Force Microscopy (AFM), detecting substantial differences in the crystallization state and grain size of the samples depending on the thermal treatment that was carried out. Moreover, AFM measurements revealed in all the treated samples a strong nanocrystallisation of the surface without evidences of amorphous matrix, which contrast with XRD measurements that have shown a high content of amorphous phase in the bulk of the ribbons. Magneto-optical Kerr effect measurements have been performed with the aim to elucidate the complex magnetic behaviour that is expected for the surface of the ribbons, measuring surface hysteresis loops that showed much higher coercive field values than that obtained in the bulk material.

Spiral magnetic domain structure in cylindrically-shaped microwires.

Identification and characterisation of novel and unusual magnetization states remains a topic of research in modern magnetism. Recently, control of the magnetization state between the surface and volume in cylindrical microwires with the giant magneto-impedance effect has been demonstrated. Herein, the phenomenon of spatial migration of spiral magnetic domains inside a microwire is demonstrated using the magneto-optical Kerr effect. The main properties of the inclined spiral structure were determined, where the surface domain structure possessed a length limited only by actual sample length. Transformation of the structure from a spiral to an elliptical structure could be controlled by external torsion stress. Hysteresis and magnetic images were simulated based on a model assuming a spatial distribution of the internal stress inside the microwire, whose results were consistent with the experimental results. A consistent interpretation of the results in terms of the formation and transformation of the spiral magnetic domain structure is proposed.

Direct imaging of the magnetization reversal in microwires using all-MOKE microscopy.

We report a method of imaging of the magnetization reversal process using analysis of real-time images of magnetic domain structures in cylindrically shaped microwires. This method uses wide-field polarizing optical microscopy and is based on the magneto-optical Kerr effect (MOKE). The aperture diaphragm in MOKE microscope was used to control the incident angles of the light rays that reached the non-planar surface of the microwire and also determined the MOKE geometries. The movement of the non-central position of the hole in this diaphragm leads to a change in the orientation of the plane of incidence of the light along the perpendicular or the parallel direction to the axial direction of the wire. The visualization of the surface magnetic domain structures is obtained using polar and longitudinal MOKE geometries. The hysteresis loops were obtained by plotting the averaged image contrast as a function of the external magnetic field. The separation of the all-magnetization components is performed using different MOKE geometries in a microscope. We demonstrate the use of vector magnetometry to analyze the orientation of the magnetization in a cylindrically shaped microwire under the influence of an external magnetic field.