Effect of the Si/B ratio on the magnetic anisotropy distribution of Fe73.5Si22.52xBxCu1Nb3 „x57,9,16… alloys along nanocrystallization

The effect of the Si/B ratio on the magnetic anisotropy distribution of Fe73.5Si22.52xBxCu1Nb3 (x57,9,16) alloys has been studied. The influence of isochronal annealing on the hysteresis loop of the three studied alloys has been analyzed. They present two minima in coercivity: the first one can be ascribed to structural relaxation, and the second one is related to the averaging of the magnetocrystalline anisotropy, as predicted by the random anisotropy model. The relative importance of both minima changes with Si content: the lower the Si content, the more effective the structural relaxation and the less important the second minimum are. The mean value of the magnetic anisotropy distribution presents a similar behavior, evidencing the growing importance of the magnetoelastic anisotropy for the relaxed amorphous samples as the Si content is increased. From the evolution of the magnetic anisotropy distribution along nanocrystallization and the microstructural information obtained from transmission electron microscopy images, the behavior of the coercivity minima with changes in Si content can be ascribed to a different degree in compensation of magnetoelastic anisotropy due to the contributions of different signs coming from the nanocrystals and the amorphous matrixCICYT. Gobierno Español-MAT95-0961-CO2-0

X-ray Structure of a (o-ga/acto-Pentaacetoxypentyl)pyrazoline

1-(3,5-Dimethyl-3-nitro-1-pyrazolin-4-yl)­ penta-0-acetyl-o-galacto-pentitol, e20H29N 3012, Mr= 503·5, orthorhombic, P21212¡, a= 14·471 (9), b = 14·518 (3), e= 12·028 (2) A, V= 2527·0 (1·7) A3, z = 4, Dx = 1·323 Mg m- 3, .A(Mo Ka)= 0·7107 A, J.L = 0·1O mm- 1, F(OOO) = 1064, room temperature, final wR = 0·035 for 1836 observed reflexions. Bond distances and ang1es are all within the expected ranges. The pyrazoline ring exhibits approximate mirror symmetry and a puckering amplitude of 0·244 (6) A. Torsion angles of the acetoxy groups with the sugar chain range from 33 to 72°. Crystal cohesion is mainly due to van der Waals interactions but there are two intermolecular hydrogen bonds o108-2701/89/1o1563-03$03.00 linking molecules related by screw axes along [100] and [001]

Microstructure and Magnetic Properties of Mo Containing Nanoperm-Type Alloys

The influence of composition changes on the devitrification process, microstructure and magnetic properties of (Fe,Co)MoB(Cu) alloys was investigated. Amorphous and nanocrystalline samples were studied by differential scanning calorimetry, thermomagnetic gravimetry, X-ray diffraction, transmission electron microscopy and vibrating sample magnetometry and obtained results are correlated. Cu addition increases the thermal stability and the crystalline fraction of the nanocrystalline microstructure and improves the soft magnetic properties of the alloy. As B content increases the thermal stability of the nanocrystalline microstructure decreases and for the 20 at.% B alloy boride crystals are formed during the first crystallization stage. Saturation magnetization decreases and Curie temperature of the amorphous phase increases with B content. Co addition lowers the volume fraction of nanocrystals and as Co content increases in the alloy nanocrystals are enriched by Co, Curie temperature of the amorphous phase increases, linearly with Co content, and saturation magnetization and coercive field of nanocrystalline alloys increase as well.Comisión Interministerial de Ciencia y Tecnología de España (CICYT) Project MAT 2004-04618Junta de Andalucía. Procesos Asistenciales Integrados (PAI

Relationship between coercivity and magnetic moment of superparamagnetic particles with dipolar interaction

The temperature dependence of the hysteresis loops of Nanoperm-type alloys has been studied. In the high-temperature region above the coercivity maximum, the response of the system can be modeled as that of dipolar-interaction superparamagnetic particles, considering a mean interaction field. Special attention has been paid to the influence of the particle size distribution on the applicability of the mean-field model. The two main effects of the dipolar interaction (coercivity and distortion of the thermal dependence of the apparent magnetic moment) have been correlated

Non-Isothermal approach to isokinetic crystallization processes: application to the nanocrystallization of HITPERM alloys

A new approach is proposed for the study of crystallization processes under the hypothesis of isokinetic behavior. From a direct extension of the Avrami theory to non-isothermal regimes, an expression of the local Avrami exponent as a function of the crystalline volume fraction is obtained from a single DSC run performed at a constant heating rate and a raw estimation of the activation energy (a variation of the activation energy value between 3 and 5 eV produces a change on the Avrami exponent smaller than ± 0.1). This approximation was applied to the nanocrystallization process of a FeCoNbB(Cu) alloy series and the results found are in good agreement with previous isothermal analysis on the same alloys. The kinetics is characterized by an initial Avrami exponent close to unity, which decreases down to values below 0.5 as the crystalline volume fraction increase

Analysis of nanocrystallization kinetics and crystal size distribution under limited growth approach

Two different simulation approaches have been used to describe nanocrystallization processes: a limited growth approach, which is an extension from instantaneous growth approximation, and an average soft impingement simulation where spherical crystallites grow to a size for which the corresponding region depleted in Fe (or the element enriched in crystalline phase) is comparable to the average distance between crystallites. Both simulations agree describing a local Avrami exponent which decreases down to ∼1 as crystallization fraction increases. Experimental data for evolution of crystal size and crystal size distribution are reproduce

Cellular automata simulations on nanocrystallization processes: From instantaneous growth approximation to limited growth

Cellular automata simulations have been performed to simulate the crystallization process under a limited growth approximation. This approximation resembles several characteristics exhibited by nanocrystalline microstructures and nanocrystallization kinetics. Avrami exponent decreases from a value n = 4 indicating interface controlled growth and constant nucleation rate to a value n ~ 1 indicating absence of growth. A continuous change of the growth contribution to the Avrami exponent from zero to 3 is observed as the composition of the amorphous phase becomes richer in the element present in the crystalline phase.Ministerio de Ciencia e Innovación de España (MICINN) y Unión Europea FEDER. MAT2010-20537Junta de Andalucía. Procesos Asistenciales Integrados (PAI) FQM-646

Structure and Absolute Configuration of l'-(p-Bromophenyl)-3'-ethyl-l',Y,4',5'- tetrahydro- 1,2-dideoxy-u-L-glucofuranoso[2,l-d]imidazole-2'-thione Monohydrate,* C15H19BrN204S.H20

M r = 421-30, monoclinic, P2~, a = 7.531 (1), b=8.148(4), c= 14. 625 (2) ,~, fl=97.14(1) °, V= 890.5 (5) ,~3, Z= 2, Din= 1.58 (1), Dx= 1.571 Mg m -3, Mo Kct, 2 = 0.7107 ,~,/~ = 2.42 mm -1, F(000)=432, T= 300 K, R =0.065 for 1672 observed independent reflexions. The sugar ring adopts a 4T 3 conformation and the dihedral angle in the bicyclic system is 72.3 (4) °. A three-dimensional network of hydrogen bonds links the molecules to build up the crystal structure

X-ray Structure and Thermal Motion of Barium N-Dithioearboxylatoglyeinate Trihydrate

Ba2+.C3H3NO2S2-.3H2 O, Mr=340.6 , triclinic, P1, a = 7.906 (1), b = 7.905 (1), c = 8.000 (1) A, ct= 96.34 (1), fl= 100.08 (1), 7= 93.54 (1)% V= 487.6 (1)A 3, Z- 2, Din= 2.31 (1), D x = 2.320 Mg m -3, 2(Mo Kct) = 0.7107/k, # = 4.47mm -1, F(000)=324, room temperature, final R = 0.044 (wR = 0.050) for 3235 observed reflexions. The anionic group is not planar and the S--C [1.717 (6) A] and C(sp2)-N [1.322 (8) A] bonds show a high double-bond character. The structure consists of infinite layers of organic anions along [100] with barium ions connected on both sides of these layers, where an extended two-dimensional hydrogen-bonding system, involving the water molecules, holds together the adjacent anions. Thermal-motion analysis reveals a good fit to a simple rigid-body model for the anion and no significant internal modes should exist