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Noble/transition bimetallic nanowires of nominal composition FexRh100-x (x = 15, 25, 54) are AC electrodeposited into 20 nm diameter hexagonally self-assembled nanopores of anodic alumina membranes. Nanowires about 18 nm in diameter and 1 μm long are polycrystalline and, depending on composition, different crystalline phases are obtained. Iron-rich (x = 54) wires are biphasic, composed by large α-Fe grains (>100 nm in length) and clusters of small (3 nm in average) grains of fcc γ-Rh(Fe) phase, with composition near (30 ± 5) at% Fe. Rh-rich (x = 15, 25) nanowires are formed by very small grains of γ-Rh(Fe) phase. Grain size depends on Rh content: grains in wires with x = 15 are the smallest with a mean size of (2.1 ± 0.9) nm. The low temperature magnetic properties of these small grained nanowires exhibit new features: they are all ferromagnetic at 5 K while, at room temperature wires with 54 at.% Fe and 25 at.% Fe are ferromagnetic and those with 15 at.% Fe are weakly superparamagnetic. These behaviors are consistent with non-compensated and very small ferrimagnetic grains surrounded by a grain boundary disordered spin-glass-like phase that freezes below 40 K. This frozen intergranular phase favors a strong exchange coupling between the ferrimagnetic grains, which undergo a cooperative, ferromagnetic-like behavior under an external magnetic field. Above 40 K nanowires with 54 at.% Fe are ferromagnetic and those containing 25 at.% Fe exhibit a ferromagnetic-like behavior arising from blocked antiferromagnetic grains. Nanowires 15 at.% Fe are weakly superparamagnetic above 40 K. Arrays containing 54 at.% Fe and 25 at.% Fe exhibit a polarization reversal mechanism involving localized nucleation and further expansion of inverse domains; this thermally activated, magnetic field assisted mechanism exhibits an apparent activation energy between 229 kJ/mol (2.3 eV) and 298 kJ/mol (3.1 eV) for nanowires 25 at.% Fe and 54 at.% Fe, respectively. Fil: Riva, Julieta Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Universidad Nacional de Cuyo; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

Arrays of SmCo nanowires (NW) and nanotubes (NT) with a diameter of 200 nm and different lengths are synthesized by electrodeposition into the nanopores of an alumina membrane. The potential applied during the synthesis largely determines the nanostructure morphology, its crystallinity and composition. Potentials investigated are between −0.8 V and −3.0 V; in the potential range between −0.8 V and 1.0 V, long and perfectly ordered nanowires are obtained with a composition close to that of the equilibrium Sm2Co17 phase in the binary alloy. For higher potentials, above −1 V, samples are nanotubes, 195 nm in external diameter and wall thickness of 30 nm with an equiatomical composition. Magnetic characterization reveals that all the nanostructures are soft ferromagnetic, with coercivity values below 60 mT. From the angular dependence of coercivity and the relative remanence it may concluded that in both, nanowires and nanotubes the magnetization reversal mechanism undergoes a transition from one at smaller angles, involving localized nucleation by curling, and further expansion of vortex-like domain walls. At higher angles, where the applied field is almost perpendicular to the NW/NT long axis, the mechanism changes to one involving nucleation by localized coherent rotation and further expansion of transverse Bloch-like walls. Fil: Herrera, Elisa Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Riva, Julieta Soledad. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Condo, Adriana Mar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energia Atomica. Gerencia D/area Invest y Aplicaciones No Nucleares. Gerencia de Física (cab). Div.física Teórica; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

As cast Cu 90 Co 10 ribbons rapidly solidified by twin-roller melt spinning, exhibit special microstructure features. This processing method provides scenarios where a different phase selection takes place; coherent Co precipitates form directly from solidification, with neither a spinodal-like composition oscillation nor a discontinuously precipitated laminar phase. Samples are processed at tangential wheel speeds of 10 m/s (V10), 15 m/s (V15), 20 m/s (V20) and 30 m/s (V30). Microstructures resulting from this single step process are characterized and the hysteresis properties and the magnetoresistance effects evaluated. Samples V30 have a quite uniform density of coherent precipitates, with a narrow size distribution around 4 nm. On contrary, non-uniform precipitate distributions are found in samples cooled at lower rates; zones with a high density of coherent Co-rich precipitates are found forming colonies. These colonies are consistent with the extended compositional fluctuations occurring during very early stages in the cooling process. Samples may exhibit wide (V10) and even bimodal (V15) size distributions. Only samples V30 behave close to the ideal superparamagnetism. Samples V20 present relatively large coercivity and relative remanence and behave as an interacting superparamagnet, while the hysteresis loops of ribbons cooled at lower rates exhibit a ferromagnetic contribution in addition to the superparamagnetic-like one. This ferromagnetic component arises from blocked precipitates, larger than the upper bound size for superparamagnetic behavior at 300 K (12 nm). Room temperature magnetoresistance values associated to granular scattering units decrease as the mean precipitate size increases, but they remain below 2%, which is lower than that measured in samples annealed after rapid solidification, indicating that in this latter case contributions from the spinodally segregated matrix take place in addition to that of Co granules. Fil: Núñez Coavas, Henry. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Pozo Lopez, Gabriela del Valle. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Condo, Adriana Maria. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina

Nucleation and growth mechanisms in Co, Cu, and CoxCu100–x single films, and in CoxCu100–x/Cu bilayers, electrodeposited on Cu70Zn30 brass substrates, are studied by the constant potential technique. The recorded current–time transients (CTTs) are rather complex, and they extend for long times. Co, Cu, and CoxCu100–x alloys electrocrystallize onto brass, undergoing a process with more than a single maximum during the CTTs, as if two or more consecutive nucleation steps were present. The first stage of electrocrystallization in Co and CoxCu100–x films involves 3D instantaneous nucleation, but then, at long times, a progressive nucleation regime predominates. CTTs in Cu/brass and in Cu/CoxCu100–x/brass bilayers are well fitted by a 2DP progressive nucleation process at the initial stage, while for longer growing times a transition to a 3DP regime is observed, in which film growth becomes controlled by adatoms incorporation to the lattice. Film morphologies observed by SEM are consistent with these growth me...

Different phase diagram measurements for succinonitrile-camphor alloys to date have yielded different values of the solute partition coefficient and the freezing range of the alloy. These parameters are critical to model solidification microstructure evolution. New measurements are made to precisely characterize the dilute limit of the succinonitrile-camphor phase diagram using thin-sample directional solidification experiments where convection is negligible, so that solute transport in the melt is purely diffusive, and the temperature gradient is constant in time. These results are confirmed through complementary measurements by differential scanning calorimetry and isothermal annealing. Possible measurement uncertainties in previously measured solidus lines are discussed. Experimental results were further confirmed using a boundary layer model of transient planar interface dynamics. Fil: Mota, F. L.. Aix-Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia. Iowa State University; Estados Unidos Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Bergeon, N.. Aix-Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia Fil: Strutzenberg, L. L.. Marshall Space Flight Center; Estados Unidos Fil: Karma, A.. Northeastern University; Estados Unidos Fil: Billia, B.. Aix-Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia Fil: Trivedi, R.. Iowa State University; Estados Unidos

Pd and PdCo nanostructures are synthesized by a soft-template route to be applied as electrocatalysts. Distinctive morphologies are obtained: nanowire-like structures, with mean diameter d = 33 nm (PdNW), forming an entangled network; nanocubes (PdNC) 64 nm in side, and PdCo(NS) nanospheres 60 nm in diameter. Pd:Co feed mol ratios (2:1) and (5:1) are used. Pd and Pd–Co nanostructures both crystallize in an fcc structure. A glassy carbon (GC) electrode is then modified with these colloidal dispersions, and further characterized by electrochemical methods. The modified PdNW/GC, PdNC/GC, and PdCoNS/GC electrodes are applied in the oxygen reduction (ORR) and oxygen evolution (OER) reactions, in a phosphate buffer pH 7 and 0.1 M NaOH solution. Voltammetric measurements are consistent with a diffusion-controlled mechanism, with a four-electron reduction process in each Pd and PdCo nanoelectrode. Resulting values of kinetic parameters indicate that the relative effectiveness of these solutions in ORR may be ordered as PdCo (5:1)NS/GC ≥ PdCo (2:1)NS/GC > PdNC/GC ≥ PdNW/GC > GC. For the OER, Tafel slopes are measured for the nanosized electrodes in both types of supporting electrolytes. Turnover frequencies estimated in alkaline solution for the OER indicate that nanostructured bimetallic PdCoNS/GC electrodes exhibit better activity than Pd/GC ones. Fil: Aguirre, María del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Rivas, Bernabé L. Universidad de Concepción; Chile Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Urreta, Silvia Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

Nd2Fe14B + α-Fe alloys have been processed by twin roller melt spinning, where the force applied to keep the rollers in contact, the only experimental variable. We found that the evolution of the equiaxed pattern in the microstructure depends on the applied force. The magnetic properties are also affected by this experimental parameter: we found that as force increases, a detriment in the BxH product is detected. These results are important because we are introducing a new control parameter in the elaboration of magnetic melt spun alloys. Fil: Levingston, Jorge Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

Norfloxacin, an antibiotic that exists in different solid forms, has very unfavorable properties in terms of solubility and stability. Binary complexes of norfloxacin, in the solid form C, and β-cyclodextrin were procured by the kneading method and physical mixture. Their effect on the solubility, the dissolution rate, and the chemical and physical stability of norfloxacin was evaluated. To perform stability studies, the solid samples were stored under accelerated storage conditions, for a period of 6 months. Physical stability was monitored through powder X-ray diffraction, high-resolution 13C solid-state nuclear magnetic resonance, and scanning electron microscopy. The results showed evidence that the kneaded complex increased and modulated the dissolution rate of norfloxacin C. Furthermore, it was demonstrated that the photochemical stability was increased in the complex, without affecting its physical stability. The results point to the conclusion that the new kneading complex of norfloxacin constitutes an alternative tool to formulate a potential oral drug delivery system with improve oral bioavailability. Fil: Garnero, Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica; Argentina Fil: Chattah, Ana Karina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Aloisio, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Longhi, Marcela Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica; Argentina

Co-Pd nanowires with small grain size are fabricated by AC electrodeposition into hexagonally ordered alumina pores, 20-35 nm in diameter and about 1 μm long. The effects of the alloy composition, the nanowire diameter and the grain size on the hysteresis properties are considered. X-ray diffraction indicates that the nanowires are single phase, a fcc Co-Pd solid solution; electron microscopy results show that they are polycrystalline, with randomly oriented grains (7-12 nm), smaller than the wire diameter. Nanowire arrays are ferromagnetic, with an easy magnetization axis parallel to the nanowire long axis. Both, the coercive field and the loop squareness monotonously increase with the Co content and with the grain size, but no clear correlation with the wire diameter is found. The Co and Co-rich nanowire arrays exhibit coercive fields and reduced remanence values quite insensitive to temperature in the range 4 K-300 K; on the contrary, in Pd-rich nanowires both magnitudes are smaller and they largely increase during cooling below 100 K. These behaviors are systematized by considering the strong dependences displayed by the magneto-crystalline anisotropy and the saturation magnetostriction on composition and temperature. At low temperatures the effective anisotropy value and the domain-wall width to grain size ratio drastically change, promoting less cooperative and harder nucleation modes. Fil: Viqueira, María Soledad. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Pozo Lopez, Gabriela del Valle. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Condo, Adriana Maria. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Cornejo, Daniel Reinaldo. Universidade de Sao Paulo; Brasil Fil: Fabietti, Luis Maria Rodolfo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina

The dynamics of plane front growth during directional solidification is investigated in a well-characterized system of succinonitrile–acetone, and the results show significant deviations from the predictions of existing models. This discrepancy is shown to arise from the assumption of solidification from one end in the theories that ignore the presence of an initial solute boundary layer generally present in experiments. A numerical model that relaxes this assumption is presented that gives excellent agreement with the experimental results.

Ni2MnGa alloys are obtained by suction casting in water chilled cylindrical copper moulds 50 mm long and 1-4 mm in diameter; the microstructure and the magnetic properties are then investigated as functions of the cylinder diameter. The solidification substructures are characterized by scanning electron microscopy and confocal microscopy. The martensitic transformation temperatures, determined by magnetization vs. temperature measurements, are lower than those measured in bulk Ni2MnGa single crystals (202 K). The demagnetization curves measured from saturation in the martensitic state show two steps: the first is at about+130 mT and the larger second one at relatively large inverse fields (about -300 mT), except in cylinders 4 mm in diameter, where these steps overlap at low inverse fields. These steps are likely to arise from a demagnetization mechanism involving field induced twin boundary motion in a few martensite variants, indicating a ferromagnetic shape memory effect in the cylinders. publishedVersion Fil: Rodoni, Esteban. Comisión Nacional de Energía Atómica. Instituto de Tecnología Sabato; Argentina. Fil: Rodoni, Esteban. Universidad de San Martín. Instituto de Tecnología Sabato; Argentina. Fil: Levingston, Jorge Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina. Fil: Levingston, Jorge Matías. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Fil: Deghi, Sebastián Esteban. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Fil: Lescano, Daniel Eduardo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Fil: Pozo López, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina. Fil: Pozo López, Gabriela del Valle. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Fil: Fabietti, Luis María Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina. Fil: Fabietti, Luis María Rodolfo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Física de los Materiales Condensados

Noble/transition bimetallic nanowires of nominal composition Fe90Rh10 are AC electrodeposited into 20 nm diameter hexagonally self-assembled alumina nanopores. Nanowires about 18 nm in diameter and 1 μm long are polycrystalline and multiphase. Wires contain α-Fe grains and very small grains of the ClCs-type α′-Fe(Rh) phase. The room temperature magnetization mechanism and the thermal stability of nanowire magnetic configurations are further investigated by measuring the dependence of the coercive field on the applied field sweeping rate R. From these data a mean fluctuations field value of μ0HFR = (9.0 ± 0.5) mT is obtained (at coercivity) and an effective activation magnetic moment μac = 5400 μB is estimated, with μB the Bohr magneton. At the coercive field (about 45 mT) the resulting activation lengths become lAC ≈ 6.4 and 6.7 nm for α-Fe and α′-Fe(Rh), respectively. Assuming an effective magnetic anisotropy, considering magnetostatic shape contributions in addition to the magnetocrystalline one, the domain wall thickness δw in α-Fe grains and in the α′-Fe(Rh) become δwFe = 13.4 nm and δwFeRh = 10.9 nm respectively. These values are comparable to the activation lengths estimated at the coercive field in each phase. These facts strongly indicate that irreversible polarization reversal in these nanowires takes place by local curling, involving localized nucleation modes. Fil: Riva, Julieta Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Condo, Adriana Maria. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Levingston, Jorge Matías. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

Stoichiometric Ni2MnGa alloys are processed by two rapid solidification techniques – single-roller (SR) and twin-roller (TR) melt spinning – and the resulting microstructures and magnetic properties determined. Samples processed at tangential wheel speeds of 10 m/s (V10) and 15 m/s (V15) are studied in the as-cast condition to analyze the influence of the production methods on the microstructure. Important aspects like the resulting phases, their crystallographic texture, magnetic properties, martensitic transformation temperatures and Curie temperatures are compared. In addition, the magnetization mechanism involving twin boundary motion is explored. Our results indicate that the TR method provides lower cooling rates, thicker samples, higher internal stresses and larger MnS precipitates. However, the quenching rate is mainly determined by the tangential wheel velocity. TR samples also exhibit [100] texture normal to the ribbon plane but in a lesser extent than SR ribbons. Martensitic transformation temperatures are higher in samples V15 (~ 150 K) than in V10 (~ 100 K), with no clear difference between the SR and TR modes. This behavior is explained by considering distinct degrees of disorder in the L21 austenite phase resulting from quenching. The hysteresis of the transformation, defined as the difference Af − MS, takes similar values in the four samples analyzed. Pre-martensitic transformation temperatures are also slightly higher in samples V15, (230 ± 3) K, than in samples V10, (222 ± 3) K, as the magnitude of the Hopkinson effect, in good agreement with a higher residual stress level in TR ribbons. In the martensitic state, all ribbons exhibit hysteresis loops characteristic of a magnetization mechanism involving twin boundary motion. The switching magnetic fields for the onset of Type I twin boundary motion result between 220 mT and 365 mT, values equivalent to twinning stresses of about 1 MPa. It is concluded that both procedures, SR and TR melt spinning, provide microstructures favoring magnetic field induced twin variant reorientation. Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Winkler, Elin Lilian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

In directional solidification experiments an alloy is placed in the thermal gradient assembly and kept stationary to achieve a steady-state thermal profile. During this time an interface motion occurs that is experimentally characterized and shown to generate a solute boundary layer at the interface whose thickness depends on the time the sample is kept stationary before the external velocity is imposed. This boundary layer must be included in the theoretical description of the initial transient during a planar front growth.

Ni2MnGa cylinders and tubes are solidified in water chilled copper molds, a few millimeters in external diameter and 5 cm long, by the suction casting technique. At room temperature, all samples are in cubic austenitic phase. Microstructure and crystallographic texture of the as-cast rods and tubes are characterized by XRD, SEM, EBSD and TEM. Because of the heat extraction geometry samples exhibit a strong texture, with the [100] direction preferentially oriented in the radial direction, together with a random distribution on the long axis. This texture is more marked in the tubes. XRD and TEM results indicate that the major austenitic phase is fcc, with L21 order. A minority volume of the equilibrium B2′ disordered phase is detected by the presence of two close Curie temperatures in cylinders and tubes 2 mm in external diameter, but not when this diameter is near 1 mm. Precipitates of the stable compounds α-Mn(S,Se), with a NaCl-type structure, and monoclinic P4S5 are observed in all the samples. Cylinders and tubes in austenitic phase are magnetically soft. Hysteresis loops in martensitic phase exhibit local steps associated to a magnetization mechanism involving twin boundary displacement, indicating that a field-induced variant reordering takes place. The switching field Hsw, corresponding to the magnetization step observed, is identified as the field at which twin boundaries become mobile. The measured values of 0.37 T–0.49 T are consistent with those corresponding to the onset of Type I twin boundaries displacement in 5 M martensite, with an equivalent threshold stress of 1 MP. Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Limandri, Silvina Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Mutal, Ruben Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Winkler, Elin Lilian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

The magnetism and the microstructure of Ni2MnGa alloys, processed by the first time by twin roller melt spinning at tangential wheel speeds of 10 m/s (V10), 15 m/s (V15) and 20 m/s (V20) are investigated. At room temperature, the major phase in the as-cast alloys is the cubic L21 Ni2MnGa ordered austenitic phase, with a lattice parameter only ~0.1% larger than the tabulated value. The order domain size in the austenitic phase decreases from (40±1) nm in samples V10 to (19±1) nm in V20. Mn(S,Se) small precipitates are also found uniformly embedded in the ribbons with mean size of (26±2) nm (V10) and (7±2) nm (V20), exhibiting a definite orientation relation with the austenitic matrix, P // a. The as-cast alloys transform to an intermediate cubic phase I at about 220K-230K depending on the quenching rate and to a martensitic phase at about 130K. The high temperature austenitic phase and the low temperature martensitic phase are ferromagnetic; in both cases the saturation polarization is lower in samples quenched at higher rates. The demagnetization curves measured from saturation in the martensitic state show two marked steps: a first one for positive fields in V15 and V10 (~46 mT) and a larger second one for relatively large inverse fields (~130-250 mT) in all the samples. These steps are likely to arise from a demagnetization mechanism involving a field induced twin boundary motion in the few martensite variants selected by the crystallographic texture and the quenched stresses in the ribbons. Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina Fil: Giordano, Rafael Nicolás. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Urreta, Silvia Elena. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Haberkorn, Nestor Fabian. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Winkler, Elin Lilian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

Fe and Fe90Rh10 (nominal) polycrystalline nanowire arrays, 20 nm in diameter and about 1-3 mm in length, are successfully synthesized by AC electrodeposition into the cylindrical pores of anodized aluminum oxide (AAO) nanotemplates. The effects of Rh addition to Fe nanowires on the resulting microstructure, magnetic hysteresis and magnetoresistance properties are explored. As deposited Fe90Rh10 nanowires are biphasic, with large alfa-Fe grains (>100 nm) and clusters of very small (1.7 nm) grains of the ClCs type a´-FeRh phase, with a composition near Fe42Rh58. Hysteresis loops as a function of the sample orientation relative to the external applied field indicate that the easy magnetization axis is parallel to the nanowire long axis at all temperatures. The coercive field decreases with rhodium addition, as expected for an effective uniaxial anisotropy controlled by shape effects; on contrary, the relative remanence (or squareness) slightly increases. The temperature dependence of the coercive field is consistent with a mechanism involving nucleation of inverse domains, with an apparent energy barrier at zero fields between 2.6 and 4.1 eV. Room temperature magnetoresistance in Fe90Rh10 arrays is negative and shows hysteresis at low fields. At low temperature a large hysteresis is observed for fields between the knees in the hysteresis loop, with field ranges of positive and negative magnetoresistance slopes, arising in domain wall nucleation and expansion to complete polarization reversal and in conventional anisotropic magnetoresistance, respectively. Fil: Riva, Julieta Soledad. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Condo, Adriana Maria. Comision Nacional de Energia Atomica. Gerencia de Area de Aplicaciones de la Tecnología Nuclear. Gerencia de Tec.nuclear Innovativa (cab); Argentina Fil: Viqueira, María Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Cornejo, Daniel Reinaldo. Universidade de Sao Paulo; Brasil Fil: Fabietti, Luis Maria Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina

The Nd 60 Fe 30 Al 10 alloy exhibits a large glass forming ability which allows to obtain relatively thick cast rods containing large volume fractions of amorphous phases. In this work the microstructure and the hard magnetic properties of as-cast rods are characterized. The alloy is processed by suction casting into a chilled copper mould to obtain cylinders 5 mm diameter and 50 mm length. This diameter is selected because it is an upper limit for this processing route, beyond which the hard properties largely deteriorate. A room temperature coercivity of 0.34 T is obtained. The sample microstructure is heterogeneous, with very different size scales near the surface and along the central zone. However, in both regions a large fraction of an amorphous ferromagnetic phase is observed; it is found that paramagnetic nanocrystalline phases – mainly Nd or Nd-rich particles, embedded in the amorphous matrix – are somewhat coarser in the central zone. These larger nanocrystals, less efficient to pin domain walls, are proposed to be responsible for the lower coercive fields observed, as compared with those found in cylinders 1–3 mm diameter where no inhomogeneities are found. This conclusion is supported by microstructure, calorimetric and magnetic observations.

The ferromagnetic amorphous phase in rapidly solidified Nd60Fe30Al10 glass forming alloys is investigated in melt spun ribbons (100 µm thick) and in chill cast cylinders (2 mm diameter). The amorphous resulting for these two different quenching rates were characterized by their room temperature hysteresis loops, magnetization and differential calorimetric measurements in the temperature range 300K-900K. The mechanical damping was explored in the 300-560 K temperature range, by measuring the internal friction and the shear modulus in a forced inverted pendulum operating in the frequency range 0.1-10Hz. Simultaneously, the electrical resistance of the samples was measured. The internal friction spectra of both, ribbons and a cylinder, exhibit a local maximum at about 500K, arising in a relaxation mechanism. After some thermal cycles the peak parameters stabilize reaching an apparent activation enthalpy of 1.5 eV and a limit relaxation time τ0 ≈ 0.4-2.5 . 10-17s. In both samples, the electrical resistance largely decreases during the first heating run to 560K and remains unchanged during subsequent thermal cycles. No changes in the elastic modulus or in the damping properties are detected at the Curie temperature of the alloys.

Soft magnetic ribbons of Finemet-type (Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ) alloys are synthesized by the twin-roller melt-spinning technique directly from the melt, at tangential wheel speeds of 15, 18, 19 and 20 m/s. The microstructure and the magnetic properties are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and hysteresis loops measurements. Samples cooled at 20 m/s are amorphous, while those quenched at lower wheel speeds are partially crystalline. All samples studied present saturation magnetization values (150–160 A m 2 /kg) higher than the commercial Finemet alloys (∼135 A m 2 /kg), obtained by controlled crystallization of amorphous single-roller melt-spun alloys. Optimal soft magnetic properties – σ S =(154±8) A m 2 /kg and H C =(6.9±0.9) A/m – are found in samples quenched at 19 m/s, consisting of size-distributed bcc Fe–Si nanograins (∼18 nm in average) embedded in an amorphous residual matrix. A minority nanocrystalline magnetic phase (≤10 nm) is also detected.

The martensitic transformation was investigated in a set of twin roller melt-spun Cu–Zn–Al shape memory alloys, solidified at tangential wheel speeds between 20 and 40 m/s. The resulting microstructures were analyzed using X-ray diffraction, optical and transmission electron microscopy techniques. The characteristic martensitic transformation temperature, M S, was determined for each condition by conventional resistometric methods. The ribbons are homogeneous in shape and for each quenching rate they exhibit a quite uniform M S temperature. By proper thermal treatments, the different factors affecting M S could be separately examined and from temperature measurements, the contribution of L21 antiphase boundaries evaluated. A calculation of this contribution using pair interchange energies is in good agreement with the experimental results.

Nanostructured Nd 60 Fe 30 Al 10 magnetic alloys were melt spun at tangential wheel speeds of 5 m/s (V5) and 20 m/s (V20). The damping and the dynamic elastic modulus were measured in an automated sub-resonant forced pendulum in both modes: at fixed frequencies between 0.1 and 1 Hz [150–480 K], and at constant temperature, varying the frequency between 1 × 1 0 − 3 and 10 Hz, always keeping constant excitation. The magnetic properties were characterized by M–H loops and by magnetization vs. temperature measurements in the same temperature range. Ferromagnetic ordering of the Fe-rich phase was observed at 460 and 410 K for samples V5 and V20, respectively. After several thermal cycles between 290 and 150 K virgin samples showed a sharp relaxation peak at 210 K (1 Hz) and a broad one at about 270 K (1 Hz), associated to a para-antiferromagnetic transition in the Nd-rich phase. The high temperature internal friction spectra at 1 Hz show an internal friction peak at T ≥ 500 K. No visible changes in the IF near the Curie temperatures are found, but there are large ‘anomalies’ in the dynamic modulus in the temperature range between the two transition temperatures, that of the Fe-rich μ -like phase and the one of the Nd-rich δ -like phase. These anomalies are significantly affected by the application of a small magnetic field (24 mT) while no changes in the IF are observed.

Nanostructured magnetic Cu-10 wt% Co alloys have been processed by ultra rapid solidification, in a twin roller melt spinning device. This solidification method (two wheels) is known to promote a more uniform microstructure as compared with that resulting in single wheel devices. The structural properties of ribbons processed at tangential wheel speeds of 5 and 23 m/s, in the as-cast condition and after a heat treatment of 1 h at 923 K, are investigated by X-ray diffraction techniques; the magnetic properties are also characterized by M–H loop measurements and the electric resistance measured as a function of the applied magnetic field at 300 K. The M–H loops can be described by the sum of a superparamagnetic like component involving small, interacting clusters of pure Co, and a soft ferromagnetic contribution which is likely to arise in the matrix. The X-ray spectra are consistent with a Cu matrix exhibiting a spinodal like Co concentration profile even in specimens in the as-cast condition. Isothermal annealing above 873 K results in the formation of larger Co clusters, in an improvement of the nominal coercivity and also leads to a higher polarization at a maximum field of 1.5 T. On the other hand, magnetoresistance effects are observed in as-cast samples solidified at 23 m/s but not in the specimen cooled at 5 m/s nor in those heat treated for 1 h at 923 K.

The hard magnetic properties of melt spun Nd 60 Fe 30 Al 10 alloys are attributed to a major matrix nominally amorphous for X-ray diffraction, composed by two metastable nanosized (∼5 nm) phases with different intrinsic magnetic properties. This composite system is investigated for the first time by mechanical spectroscopy techniques in the temperature range between 50 K and 450 K (1 kHz) where large annealing effects and two damping phenomena are detected. The as-cast microstructure irreversibly changes during annealing above 330 K, leading to a large modulus recovery accompanied by a reduction in the internal friction level. A relatively large relaxation effect is observed about 290 K, evidenced by a narrow internal friction peak with the corresponding step in the elastic modulus; this peak remains stable under thermal cycling between 200 K and 300 K but is affected by aging at 330 K and practically vanishes after heating to 450 K. Another internal friction peak is observed at about 250 K which has associated an anomalous modulus effect; in this temperature range, the internal friction and the elastic modulus exhibit heating/cooling hysteresis, which strongly depends on the extreme temperatures of the thermal cycle, a behavior frequently associated to first-order phase transformations.

Alloys with compositions Nd60−xCxFe30Al10 (x=0, 1, 5 and 10) were processed by melt spinning at a tangential speed of 5 m/s. The as-cast ribbons were characterized by X-ray diffraction, Mossbauer Effect spectroscopy and their room temperature hysteresis loops. The substitution of Nd by C is found to affect the phase selection, from mainly DHCP-Nd for x=0 to DHCP-Nd /FCC-Nd for the other ones. Mossbauer spectra of all the as-cast samples indicate that Fe is present in crystalline magnetic phases as well as in a paramagnetic one. The major crystalline phase was identified as a μ-type (or A1) metastable phase, which is reported to have a large anisotropy field and a relatively high saturation polarization. Interstitial C stabilizes the μ-type phase and improves its average hyperfine field. The magnetic measurements display an increase of coercivity and remanence with the C concentration.

The effects of the cooling rate on the microstructure and magnetic properties of the melt-spun Nd60Fe30Al10 alloys are investigated by Mossbauer Effect (ME) spectroscopy and magnetic hysteresis loops measurements at different temperatures. It is found that the hard magnetic properties of these alloys are likely to be related to the presence of clusters of a metastable crystalline μ-type phase. It is observed that as the cooling rate increases, the amount of this magnetic μ-like phase component decreases in the benefit of an amorphous Nd-rich phase. This phase has an iron concentration, which increases with increasing the wheel speed, is paramagnetic at room temperature and becomes superparamagnetic below approximately 50 K and 100 K for slow and high cooling rates, respectively.

The local atomic arrangements and the nanoscopically dispersed phases in melt spun Nd 60 Fe 30 Al 10 alloys are investigated by Mōssbauer spectroscopy. It is found that the hard magnetic properties of these alloys are likely to be related to the presence of clusters of a metastable crystalline μ-type phase.

Hysteresis and relaxation properties of Nd 60 Fe 30 Al 10 partially amorphous alloys, processed by melt spinning at 5 m/s (V5), 10 m/s (V10) and 20 m/s (V20), are investigated. Specimens V20 show two-step hysteresis loops while relatively square loops, exhibiting magnespring effects, are found in samples V5. In these latter microstructures, the demagnetization process has associated a nearly constant fluctuations field of μ 0 H f =14.5 mT , and a characteristic activation length l ac =7 nm . These values are similar to those obtained for V10 and V20 at the hard irreversible susceptibility peak: 13.1 mT, 7.3 nm (V10) and 13.5 mT, 7.1 nm (V20), respectively. In specimens V5, hysteresis and thermal relaxation are controlled by the same distribution of energy barriers and the results obtained are consistent with a reversion process involving a nucleation mechanism in a magnetic grain of size l mg ∼ l ac , with l mg the exchange length in the amorphous phase. This characteristic length is estimated by considering the amorphous phase as a two-phase magnetic composite in which the hard Fe-rich clusters are coupled by exchange interactions, mediated by a surrounding Nd-rich phase.

The demagnetization processes in Nd 2 F 14 B+αFe nanocrystalline composites exhibiting square and two-step hysteresis loops are investigated. In all these microstructures, an expanding nucleus model (Global Model) reasonably describes the experimental results in the entire range of the demagnetization loop, provided different sites acting as inverse nucleus are considered. Nucleation is found to take place in both phases and under different coupling conditions exhibiting, in each case, a different reversion regime. Each regime has associated definite values of specific nucleus surface energy and effective local demagnetizing factor, which are similar in all the specimens, in spite of their different microstructures and compositions. These specific surface energy values are close to those expected for domain wall-like configurations resulting from competing interactions in the particular nucleation site, not always related to the intrinsic properties of the phase itself but largely determined by inter-grain interactions.

Nanostructured Nd 60 Fe 30 Al 10 magnetic alloys were obtained by melt spinning at a tangential wheel speed of 5 m/s. Magnetic and stress relaxation processes were investigated in the as cast condition. Low frequency mechanical spectroscopy studies (dynamic elastic torsion modulus and internal damping measurements) were conducted at fixed frequencies between 0.1 and 1 Hz, in the range [150–480 K]. The low temperature internal damping and dynamic elastic modulus exhibited a large heating–cooling hysteresis and two damping peaks: one due to a stress induced relaxation mechanism operating near 200 K [1 Hz] and another one, at about 260–270 K, which could not be correlated with any step in the modulus, indicating that it is not anelastic in origin. The high temperature damping was described by an exponential background and a broad peak contribution centered at about 400 K (1 Hz). The resulting maximum is frequency dependent, but it is little sensitive to applied fields up to 30 mT. On contrary, the elastic modulus behavior associated to this maximum resulted largely affected by frequency, the external fields and the magnetic state of the sample.

The intrinsic values of the magnetic viscosity and the fluctuation field in a two phase composite Nd 2 Fe 14 B+0.18 vol. αFe were investigated. The composite studied, with equiaxed and isotropically oriented grains had mean grain sizes favoring a strong exchange coupling between the phases. The relations between the intrinsic and the experimentally measured magnitudes are reviewed and the approximations discussed. For applied fields close to the coercivity, the time dependence of the magnetization is not well described by a simple logarithmic law. The intrinsic fluctuation field is found to increase when the reverse internal field increases in all the ranges investigated and two different regimes are identified. These different regimes are discussed considering the distributions of critical fields for nucleation of inverse domains in the hard phase, at hard–soft and hard–hard grain boundaries, respectively.

The magnetomechanical coupling in a nanocrystalline ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}+0.18 \mathrm{vol} \ensuremath{\alpha} \mathrm{Fe}$ composite is investigated using mechanical spectroscopy technics. The internal friction and the elastic modulus are simultaneously measured between 4 and 300 K (800 Hz, $\ensuremath{\epsilon}l~{10}^{\ensuremath{-}4}).$ The composite magnetization is also measured as a function of temperature in the same range. The experiments are performed in the same sample exhibiting two different magnetic states. The state I is thermally demagnetized and domain walls are found in both phases. The state II, in which $\ensuremath{\alpha}$ Fe is saturated and the ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ grains are single domains, is attained by applying a dc magnetic field of 4.5 kOe during measurements. The elastic modulus increases during heating and in both states this recovering is correlated with the irreversible changes in the composite magnetization. The internal damping in the sample with a single domain configuration (state II) is higher than that found when both phases have multidomain grains (state I) in all the range investigated. Large contributions to the mechanical dissipation are related to irreversible changes in the magnetization by a nucleation mechanism in the ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ grains.

The dependence on the mean grain size of the magnetic properties of isotropic nanocrystalline FeNdB+αFe composite magnets has been investigated. The grain size distribution was varied by changing the melt spinning conditions. It is found that both, the remanence and the coercivity increase as the mean grain size of the hard phase decreases from 80 to 25 nm, in good agreement with micromagnetic numerical calculations. The behavior of these properties is consistent with a process of exchange hardening of the soft phase as the grain size decreases. The effect of exchange coupling between different grains may be considered by introducing in the nucleation term of the modified Brown's equation a factor depending on the grain size distribution.

The process of interface pattern formation in a complex crystal structure is examined through directional solidification experiments in the tert butyl alcohol (TBA) - water system. The transition from a planar interface to cellular and needle morphologies with increasing velocity is examined. The anisotropic effects in the complex crystal structure have been shown to exhibit new features that have not been observed previously. The anisotropy effects have been found to preclude cell elimination and cell creation by the tip splitting processes, so that the wavelength of the cellular pattern is determined by the initial wavelength of perturbation on a planar interface. At higher velocities, a cellular structure is found to transform to a needle structure with highly faceted sides which stabilize the interface against sidebranch instability. The tip region of the needle morphology also exhibits a unique structure that resembles a fingernail, whose formation is governed by the anisotropic properties of the advancing interface. In this complex crystal structure, the growing planes are not symmetrical and the growth occurs preferentially only along specific orientations of the advancing interface which give rise to a fingernail morphology. The scaling law for the primary spacing and the variation of interface temperature with velocity have been found to show a behavior analogous to that for isotropic materials.

Directional solidification experiments have been carried out to examine in situ the stress generated at the interface which lead to the formation of defects. A transparent system, which is also birefringence, is selected for the study to observe simultaneously both the morphology of the interface and the stress fringes. For a cusp orientation, the instability of the interface is shown to give rise to stress generation, and when sufficient stress accumulates, a grain boundary is formed to relieve the stress. A stress-induced parallel grain boundary formation is shown to be the mechanism for planar-to-cellular interface transition. The same mechanism is shown to cause cellular tip splitting to adjust the cellular spacing. A simple model of stress generation due to concentration gradients near the perturbed interface is developed to show the possible mechanism of stress generation.

The glass-forming Nd 60 Fe 30 Al 10 alloy, processed by melt spinning, exhibits hard magnetic properties. For a relatively wide range of quenching rates, a single magnetic phase behavior is observed at room temperature, with coercivities between 0.1 and 0.4 T. As the quenching rate decreases, the hard magnetic properties improve and the thermal stability of the resulting magnetic microstructure—as measured by the reciprocal of the mean fluctuations field H f —decreases. The hysteresis and thermal relaxation properties observed for different cooling rates are discussed on the basis of domain wall movement in a ferromagnetic matrix in which small, highly anisotropic clusters develop as the quenching rate decreases.

Ferromagnetic amorphous Nd 60 Fe 30 Al 10 alloys melt spun at wheel speeds between 5 and 20 m/s exhibit hard magnetic properties, which are found to be very sensitive to the cooling conditions. The magnetization reversion mechanisms leading to the rather high coercive forces found are investigated by thermally activated magnetic relaxation experiments; the mean fluctuation field and the activation volume are measured—in specimens cooled at different rates—at the critical field for extensive magnetization reversion. These preliminary results show a qualitative agreement with the predictions of a ferromagnetic cluster model.

Polycrystalline CoxPd1-x (x=1, 0.60, 0.45, 0.23, and 0.11) cylindrical nanowires (ø=18-35nm, about 1μm length) are produced by AC electrodeposition into hexagonally ordered alumina pores. Single-phase nanowires of an fcc Co-Pd solid solution, with randomly oriented equiaxed grains (7-12nm) are obtained; in all the cases, the grain size is smaller than the wire diameter. The coercive field and the reduced remanence of Co-rich nanowire arrays are hardly sensitive to temperature within the range varying from 4K to 300K. On the other hand, in Pd-rich nanowires both magnitudes are smaller and they largely increase when cooling below 100K. This behavior also depends on the mean grain size. These facts are systematized considering two main aspects: the non-trivial temperature and composition dependence of the crystalline anisotropy and the saturation magnetostriction in Co-Pd alloys; and a random anisotropy effect, which defines a nucleation localization length that may involve more than a single grain, and thus promotes more cooperative nucleation modes. Fil: Viqueira, María Soledad. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Pozo Lopez, Gabriela del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Urreta, Silvia Elena. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Condo, Adriana Maria. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Cuyo; Argentina Fil: Cornejo, Daniel Reinaldo. Universidade de Sao Paulo; Brasil Fil: Fabietti, Luis Maria Rodolfo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina