Publications (4)1.39 Total impact

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    ABSTRACT: We present a spin resonance investigation of the family of quasi- two-dimensional organic (super)conductors &''circ; -(ET)4-[(H3-O)M-(C2-O4)3]S (M = Cr^ 3+, Fe^3+; S is a guest molecule). The spin systems are probed by means of both resonant cavity perturbation and field modulation techniques in the frequency range 50-313 GHz. The role of the different solvent molecules in determining the degree of spin-orbit coupling and the local symmetry at the metal ion site is established. Intensities, positions and widths of the resonant lines reveal significant modifications of the spin-orbit coupling, and of the inter- and intra-ionic spin-spin interactions below T=10K. Despite the onset of a weak antiferromagnetic internal field at low temperature, the ultimate narrowing of the lines suggests spin-lattice interactions are still the dominant relaxation process. Additional lineshifts observed below B = 2.5 T and T = 4 K, attributed to the presence of diamagnetic currents in the mixed state of the superconducting samples, provide a threshold for full field penetration within the ``insulating" anion layers.
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    ABSTRACT: We report a spin resonance study of the family of quasi-two-dimensional organic (super)conductors β”-(BEDT-TTF)4[(H3O)M(C2O4)3]S, where M is a 3d transition metal ion and S is a host solvent molecule. The spin systems for M = Cr3+ (S = 3/2) and M = Fe3+ (S = 5/2) are investigated by means of both resonant and field modulation techniques in the frequency range between 50 and 313GHz. The role of the different solvent molecules in determining the degree of spin-orbit coupling and the local symmetry at the metal ion site is established. The low temperature behaviour of intensities, positions and widths of the resonant lines shows significant modifications of the spin-orbit coupling, and of the inter-and intra-ionic spin-spin inter actions. Despite the onset of a weak antiferromagnetic internal field at low temperature, the ultimate narrowing of the lines suggests spin-lattice interactions may still be the dominant relaxation process. Diamagnetic screening in the mixed state of the superconducting samples for fields parallel to the quasi-two-dimensional layers induces additional lineshifts only below B = 2.5T and T = 4K, determining the threshold of full field penetration within the anion layers.
    Journal of Low Temperature Physics 01/2006; 142(3):581. DOI:10.1007/s10909-006-9149-0 · 1.04 Impact Factor
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    ABSTRACT: We report a spin resonance study of the family of quasi-two-dimensional organic (super) conductors β″-(BEDT-TTF)4[(H3O)M(C2O4)3]S, where M is a 3d transition metal ion and S is a host solvent molecule. The spin systems for M=Cr3+ (S=3/2) and M=Fe3+ (S=5/2) are investigated by means of both resonant and field modulation techniques in the frequency range between 50 and 313 GHz. The role of the different solvent molecules in determining the degree of spin-orbit coupling and the local symmetry at the metal ion site is established. The low temperature behaviour of intensities, positions and widths of the resonant lines shows significant modifications of the spin-orbit coupling, and of the inter- and intra-ionic spin-spin interactions. Despite the onset of a weak antiferromagnetic internal field at low temperature, the ultimate narrowing of the lines suggests spin-lattice interactions may still be the dominant relaxation process. Diamagnetic screening in the mixed state of the superconducting samples for fields parallel to the quasitwo-dimensional layers induces additional lineshifts only below B=2.5 T and T=4 K, determining the threshold of full field penetration within the anion layers.
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    ABSTRACT: We applied magneto-optical techniques to investigate the electron spin resonance (ESR) spectra of single crystal and powder samples of the organic superconductor beta''-(BEDT- TTF){4}[ (H{3}O)Fe (C{2}O{4}){3}] C{6}H{5}CN. Data were obtained in magnetic fields up to 10 Tesla using both cylindrical and rectangular resonators at 55, 63 and 72 GHz and transmission measurements at 95 and 190 GHz with field modulation. Analysis of the high field-high frequency ESR lines for different field orientations and temperatures allows the determination of the g-value anisotropy and the zero-field splitting parameters for the Fe3+ ions (S=5/2), showing that they occupy a site with distorted octahedral symmetry. The temperature and frequency dependences of the magneto-optical spectra are used to identify the nature of the interaction between localised Fe spins and between the local moments and the delocalised carriers. Key words. Electron Spin Resonance. Antiferromagnetism. Type-II superconductor. Vortex state.
    Journal de Physique IV (Proceedings) 01/2004; 114:347-349. DOI:10.1051/jp4:2004114079 · 0.35 Impact Factor