National Institute Of Materials Physics - Romania

Local magnetic interactions and spin configurations in alpha-Fe/Nd2Fe14B composite exchange-spring magnets have been investigated by Mossbauer spectroscopy and the magnetic behaviour was analysed by magnetometry. A new method for the evaluation of the coupling strength between soft and hard magnetic phases is proposed. (C) 2003 Elsevier B.V. All rights reserved.

The bimetallic AgCo nanoparticles synthesized by colloidal chemistry and deposited onto Si(100) substrate are investigated. Size-selective mechanisms of colloidal crystallization during the self-organization are evidenced. The magnetic behavior is studied and correlated with the nanoparticles structure and morphology. (C) 2003 Elsevier B.V. All rights reserved.

The magnetic interactions and the Fe spin structure have been studied in Fe(6 nm)/FeRh systems by magnetometry, magneto-optic Kerr effect and conversion electron Mossbauer spectroscopy. A spin-flop coupling mechanism, with the interfacial spins of the ferromagnetic phase perpendicular to the spins of the antiferromagnetic phase was experimentally proved. (C) 2004 Elsevier B.V. All rights reserved.

Colloidal solutions of magnetic nanoparticles are regularly dispersed onto patterned substrates in order to form novel magnetic nanostructures. The morphology of these nanostructures is investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM) and their structure is correlated with magnetic properties. It is shown that, depending on the nature of the substrate, different nanoparticle growth modes are identified during the colloidal crystallization. (C) 2003 Elsevier B.V. All rights reserved.

The effect of rare earth addition in the structure and magnetism of melt spun nanocrystalline Finemet-type alloys devitrified from amorphous precursor ribbons is discussed. Starting with the initial composition Fe73.5Cu1Nb3Si13.5B9 an amount of 5 at% Gd is introduced into the primary alloy. The purpose is to enable after appropriate recrystallization the occurrence of hard and soft magnetic, suitably dispersed, exchange-coupled nanograins and to determine the transformation sequences of the crystallization process and the obtained crystallization products. (C) 2003 Elsevier B.V. All rights reserved.

AC susceptibility measurements have been performed on Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox (Bi-2223) samples doped with different Li-based compounds and prepared by the solid-state method. As-prepared samples and/or samples annealed in oxygen or argon, ground or unground, have been investigated in detail in order to understand the occurrence, nature and evolution of the anomalous peaks observed in chi " (T) curves versus the measuring parameters; we have detected up to four peaks instead of the usual two peaks observed in the non-doped samples. It was found that intrinsic physical-chemical properties, such as the melting temperature of the doping compound, are no less important for the final properties of the superconductor than their insertion properties into the crystal lattice of Bi-2223. Doping compounds with melting temperatures below or close to the phase formation temperature of the Bi-2223 phase can act as flux, changing the growth conditions. Intensification of some processes against others (e.g. decomposition-recovery of the BI-2223 phase, solubilization-precipitation of the secondary phases, changes in the properties of the liquid phase, etc) can lead to the formation of the Bi-2223 phase with different properties than for the non-doped superconductor. Generally, when using flux-type doping compounds, anomalous AC losses peaks are detected and the intra-granular critical current density is enhanced.

The reaction of the neutral cluster [Fe2BaO(CCl3COO)(6)(THF)(6)] with Eu(NO3)(3) . 6H(2)O in methanol affords novel tetra-nuclear Fe-Eu complex [Fe3EuO2(CCl3COO)(8)H2O(THF)(3)] . THF (1), which displays interesting Mossbauer spectra and magnetic behaviour. (C) 2004 Elsevier B.V. All rights reserved.

NdNiSnD and PrNiSnD monodeuterides have been studied by Sn-119 Mossbauer spectroscopy at variable temperatures between 4.2 and 300 K. Deuterium insertion into the RE3Ni sites induces at low temperatures a magnetic splitting of the tin nuclear levels. Slightly different magnetic ordering temperatures, 25(1) and 20(1) K, were evidenced for the Nd- and Pr-containing deuterides, respectively. The Mossbauer spectra suggest a similar type of local structures for both compounds, with a mutual substitution of Sn and Ni atoms. The magnetic behaviour is discussed in relation to the different spin waves mechanisms. (C) 2003 Elsevier B.V. All rights reserved.

(Cu, C)Ba2Ca3Cu4Ox superconductor with addition of y mol LiF has been synthesized by a high-pressure method. For the same synthesis conditions it was found that (almost) single-phase Cu, C-1234 samples can be synthesized for y(LiF) = 0-0.1 if the amount of z mol AgO oxidizer is increased linearly from Z(AgO) = 0.45 to 0.73 and for y(LiF) = 0 - 1-0.2 if ZAgO = 0.73 = constant. Transport measurements (rho(T) and room-temperature Seebeck coefficient) have shown that these samples are overdoped: LiF is an effective addition for synthesis of overdoped Cu, C-1234 with a controlled level of carriers. LiF addition continuously decreases T-c. The critical point at y(LiF) = 0.1 is discussed as the solubility limit of LiF and/or the point where the doping mechanism changes. It is proposed that the reason is the reaction of extra Li with C and O to form Li2CO3, inducing a lower concentration of C in Cu, C-1234/LiF crystals, and at the same time a possible substitution of Li not only for the Cu site but also for the Ca site, resulting in formation of a higher amount of residual Ca0.828CuO2 (for y(LiF) > 0.1). LiF induces the formation of a liquid phase and acts as a flux promoting the formation of Cu, C-12(n - 1)n with n greater than or equal to 4. LiF modifies to some degree the grain growth from a 3D to a 2D type (thinner platelike grains have been observed in the LiF added samples).

Critical current density J(c) of Na0.35CoO2.1.3H(2)O superconductor (T-c=4.4 K) has been estimated from magnetization measurements: J(c)(1.9 K,0 T)=5x10(4) A/cm(2), J(c) (1.9 K,0.4 T)=4x10(2) A/cm(2) and J(c) (3.4 K,0 T)=10(3) A/cm(2). J(c) versus applied magnetic field H cannot be fitted, as for high-T-c superconductors (HTS), by a power law for any temperature. The temperature dependence for a given H is not of the linear type as for MgB2, but is close to quasiexponential (associated with the thermally activated flux creep) as for HTS. Irreversibility field data points H-irr versus (1-T/T-c) obey a power law with power exponent n=3.4. The irreversibility line is located below, but in vicinity of, the line for Bi-2223. Details of morphology are also presented. (C) 2004 American Institute of Physics.