Magnetic Reflectivity Research Articles

Soft x-ray resonant magnetic reflectivity study of thin films and multilayers

Soft x-ray resonant magnetic reflectivity measurements on thin films and multilayers in a transverse geometry using linear polarized photons are presented. Magneto-optic calculations taking into account the layer roughness allows us to reproduce all the experimental features of the angular and energy reflectivity curves as well as the asymmetry ratio in both cases. Application to FexMn1−x alloy films epitaxially grown on Ir(001) brings more insights on the magnetic transition occurring at x=0.75.

On bistability in molecular systems: Photomagnetic studies of inorganic complexes

Photo‐induced effects have been detected by magnetic measurements, Mossbauer spectroscopy and reflectivity. The LIESST effect has been achieved in the spin‐crossover system [FexCo1-x(btr)2(NCS)2]·H2O. We investigated the purely photo‐induced magnetism of a Prussian Blue analogue Rb0.52Co[Fe(CN)6]0.84, 2.31 H2O, involving an optical electron transfer from FeII to CoIII. Inherent aspects of photomagnetic experiments are described: bulk and surface effects, magnetic and electronic metastabilities of the photo‐excited state.

Magnetic effects on the resonant X-ray reflectivity: circular dichroism at the 2p edges of Ni

We measured the X-ray reflectivity of a Ni(110) crystal over the photon energy range including the 2p absorption edges of Ni. Using circularly polarized X-rays, we observed large variations in the resonant reflectivity according to the relative orientation between sample magnetization and photon helicity. The angular dependence of the dichroism and the use of resonant magnetic reflectivity for drawing hysteresis curves are also discussed.

Electron correlation and magnetism in dilute metals

The effects of electron-electron interactions on the magnetic properties of alkali metals are reviewed. At the densities of the solid or liquid near the melting point, magnetic properties are well described by a generalization of the Stoner model. This approach accounts for enhancement of the magnetic susceptibility and deviations from the Korringa relation between the NMR Knight shift and the corresponding contribution to nuclear spin-lattice relaxation. When expanded by heating the liquid toward the liquid-gas critical point, the magnetic properties and optical reflectivity of caesium develop new characteristics best described by correlation enhancement of the effective mass. Behaviour of the Korringa relation deviation implies a change in the spin correlations from essentially ferromagnetic in the dense liquid to antiferromagnetic in the dilute metal. The similarity of these effects to those observed in the high Tc superconducting cuprates is discussed.

Compositional dependence of the band structure and magnetic properties of PbSnMnTe narrow-gap semimagnetic semiconductor

Low-temperature measurements of the magnetic susceptibility, plasma reflectivity and Hall effect as a function of carrier-concentration were performed on Pb1-x-ySnxMnyTe samples with x=0.72 and y=0.03, 0.06, 0.08. The dependences of the paramagnetic Curie temperature and effective mass of holes on manganese content and carrier concentration were determined. The analysis of the experimental data has been performed assuming that two valence bands are relevant in the case of PbSnMnTe: the non-parabolic light-hole L band and the parabolic heavy-hole Sigma band. Theoretical calculations of the paramagnetic Curie temperature dependences on manganese content and carrier concentration were also performed on the basis of the band structure model mentioned above and assuming the RKKY exchange interaction between Mn spins. It was found that the compositional evolution of the band structure determined the carrier concentration dependence of the magnetic properties of PbSnMnTe.

New electrically conductive polymers. Dopant and architectural effects on the collective properties of cofacially joined metallophthalocyanines

AbstractAn integrated chemical and physicochemical investigation of the cofacially joined metallomacrocyclic polymers [M(Pc)O]n (M = Si, Ge, Si) and the halogen‐doped, electrically conductive derivatives {[M(Pc)O]Xy}n (X = I; M = Si, Ge; X = Br; M = Si) is reported. The structures of these polymers have been studied by X‐ray diffraction, resonance Raman, transmission infrared, transmission optical, 13C CP‐MAS NMR, and EPR spectroscopy. The picture which emerges is that of inhomogeneously doped, mixed‐valent arrays of predominantly ligand‐oxidized (π radical cation) metallomacrocycles. Magnetic susceptibility and optical reflectivity measurements reveal a progressive increase in tight‐binding bandwidths with decreasing interplanar (ring‐ring) spacing. Studies of dc electrical conductivity as a function of dopant level and temperature suggest that transport in these heterogeneously doped materials can be satisfactorily described with percolation theory and fluctuation‐induced carrier tunneling. The conductivity is a sensitive function of the ring‐ring stacking separations; evidence is presented for “metal‐like” (dσ/dt < O) conductivity in the {[Si(Pc)O]I1.12}n stacking direction with σ ≈ 100 Ω−1 cm−1.