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Börje Johansson - One of the best experts on this subject based on the ideXlab platform.

  • pressure induced invar effect in fe ni Alloys
    Physical Review Letters, 2001
    Co-Authors: Leonid Dubrovinsky, Börje Johansson, Mark Van Schilfgaarde, Igor A Abrikosov, Natalia Dubrovinskaia, Marie Vennstrom, F Westman, Stefan Carlson
    Abstract:

    We have measured the pressure-volume (P-V) relations for cubic Iron-Nickel Alloys for three different compositions: Fe 0.64Ni (0.36), Fe 0.55Ni (0.45), and Fe 0.20Ni (0.80). It is observed that for a certain pressure range the bulk modulus does not change or can even decrease to some minimum value, after which it begins to increase under still higher pressure. In our experiment, we observe for the first time a new effect, namely, that the Fe-Ni Alloys with high Ni concentrations, which show positive thermal expansion at ambient pressure, become Invar system upon compression over a certain pressure range.

  • origin of the invar effect in iron nickel Alloys
    Nature, 1999
    Co-Authors: Mark Van Schilfgaarde, Igor A Abrikosov, Börje Johansson
    Abstract:

    In 1897 Guillaume1 discovered that face-centred cubic Alloys of iron and nickel with a nickel concentration of around 35 atomic per cent exhibit anomalously low (almost zero) thermal expansion over a wide temperature range. This effect, known as the Invar effect, has since been found in various ordered and random Alloys and even in amorphous materials2. Other physical properties of Invar systems, such as atomic volume, elastic modulus, heat capacity, magnetization and Curie (or Neel) temperature, also show anomalous behaviour. Invar Alloys are used in instrumentation, for example as hair springs in watches. It has long been realized that the effect is related to magnetism2,3; but a full understanding is still lacking. Here we present ab initio calculations of the volume dependences of magnetic and thermodynamic properties for the most typical Invar system, a random face-centred cubic iron–nickel alloy, in which we allow for non-collinear spin alignments—that is, spins that may be canted with respect to the average magnetization direction. We find that the magnetic structure is characterized, even at zero temperature, by a continuous transition from the ferromagnetic state at high volumes to a disordered non-collinear configuration at low volumes. There is an additional, comparable contribution to the net magnetization from the changes in the amplitudes of the local magnetic moments. The non-collinearity gives rise to an anomalous volume dependence of the binding energy, and explains other peculiarities of Invar systems.

Michael Matlosz - One of the best experts on this subject based on the ideXlab platform.

  • competitive adsorption effects in the electrodeposition of iron nickel Alloys
    Journal of The Electrochemical Society, 1993
    Co-Authors: Michael Matlosz
    Abstract:

    Two-step reaction mechanisms involving adsorbed monovalent intermediate ions for the electrodeposition of iron and nickel as single metals can be combined to form a predictive model for the codeposition of Iron-Nickel Alloys. Inhibition of the more noble nickel in the presence of iron is caused by preferential surface coverage of the adsorbed iron intermediate resulting from a difference between the two elements in Tafel constant for the electrosorption step. The role of hydrolyzed cations and surface pH is investigated and methods for evaluating the influence of pH are explored. The analysis shows that changes in surface pH with potential are not necessary for iron-rich (anomalous) deposits, but that variations in pH from one electrolyte to another may influence deposit composition. The tendency toward iron-rich deposits with increasing overpotential exists in all systems, however, and can be prevented only by decreasing the iron concentration of the bath. An extension of the analysis to account for transport limitations in baths with low iron concentration is developed and calculations with the model are presented to illustrate the effects of current density and electrolyte convection under conditions similar to those investigated experimentally in the literature.

Mark Van Schilfgaarde - One of the best experts on this subject based on the ideXlab platform.

  • pressure induced invar effect in fe ni Alloys
    Physical Review Letters, 2001
    Co-Authors: Leonid Dubrovinsky, Börje Johansson, Mark Van Schilfgaarde, Igor A Abrikosov, Natalia Dubrovinskaia, Marie Vennstrom, F Westman, Stefan Carlson
    Abstract:

    We have measured the pressure-volume (P-V) relations for cubic Iron-Nickel Alloys for three different compositions: Fe 0.64Ni (0.36), Fe 0.55Ni (0.45), and Fe 0.20Ni (0.80). It is observed that for a certain pressure range the bulk modulus does not change or can even decrease to some minimum value, after which it begins to increase under still higher pressure. In our experiment, we observe for the first time a new effect, namely, that the Fe-Ni Alloys with high Ni concentrations, which show positive thermal expansion at ambient pressure, become Invar system upon compression over a certain pressure range.

  • origin of the invar effect in iron nickel Alloys
    Nature, 1999
    Co-Authors: Mark Van Schilfgaarde, Igor A Abrikosov, Börje Johansson
    Abstract:

    In 1897 Guillaume1 discovered that face-centred cubic Alloys of iron and nickel with a nickel concentration of around 35 atomic per cent exhibit anomalously low (almost zero) thermal expansion over a wide temperature range. This effect, known as the Invar effect, has since been found in various ordered and random Alloys and even in amorphous materials2. Other physical properties of Invar systems, such as atomic volume, elastic modulus, heat capacity, magnetization and Curie (or Neel) temperature, also show anomalous behaviour. Invar Alloys are used in instrumentation, for example as hair springs in watches. It has long been realized that the effect is related to magnetism2,3; but a full understanding is still lacking. Here we present ab initio calculations of the volume dependences of magnetic and thermodynamic properties for the most typical Invar system, a random face-centred cubic iron–nickel alloy, in which we allow for non-collinear spin alignments—that is, spins that may be canted with respect to the average magnetization direction. We find that the magnetic structure is characterized, even at zero temperature, by a continuous transition from the ferromagnetic state at high volumes to a disordered non-collinear configuration at low volumes. There is an additional, comparable contribution to the net magnetization from the changes in the amplitudes of the local magnetic moments. The non-collinearity gives rise to an anomalous volume dependence of the binding energy, and explains other peculiarities of Invar systems.

Igor A Abrikosov - One of the best experts on this subject based on the ideXlab platform.

  • pressure induced invar effect in fe ni Alloys
    Physical Review Letters, 2001
    Co-Authors: Leonid Dubrovinsky, Börje Johansson, Mark Van Schilfgaarde, Igor A Abrikosov, Natalia Dubrovinskaia, Marie Vennstrom, F Westman, Stefan Carlson
    Abstract:

    We have measured the pressure-volume (P-V) relations for cubic Iron-Nickel Alloys for three different compositions: Fe 0.64Ni (0.36), Fe 0.55Ni (0.45), and Fe 0.20Ni (0.80). It is observed that for a certain pressure range the bulk modulus does not change or can even decrease to some minimum value, after which it begins to increase under still higher pressure. In our experiment, we observe for the first time a new effect, namely, that the Fe-Ni Alloys with high Ni concentrations, which show positive thermal expansion at ambient pressure, become Invar system upon compression over a certain pressure range.

  • origin of the invar effect in iron nickel Alloys
    Nature, 1999
    Co-Authors: Mark Van Schilfgaarde, Igor A Abrikosov, Börje Johansson
    Abstract:

    In 1897 Guillaume1 discovered that face-centred cubic Alloys of iron and nickel with a nickel concentration of around 35 atomic per cent exhibit anomalously low (almost zero) thermal expansion over a wide temperature range. This effect, known as the Invar effect, has since been found in various ordered and random Alloys and even in amorphous materials2. Other physical properties of Invar systems, such as atomic volume, elastic modulus, heat capacity, magnetization and Curie (or Neel) temperature, also show anomalous behaviour. Invar Alloys are used in instrumentation, for example as hair springs in watches. It has long been realized that the effect is related to magnetism2,3; but a full understanding is still lacking. Here we present ab initio calculations of the volume dependences of magnetic and thermodynamic properties for the most typical Invar system, a random face-centred cubic iron–nickel alloy, in which we allow for non-collinear spin alignments—that is, spins that may be canted with respect to the average magnetization direction. We find that the magnetic structure is characterized, even at zero temperature, by a continuous transition from the ferromagnetic state at high volumes to a disordered non-collinear configuration at low volumes. There is an additional, comparable contribution to the net magnetization from the changes in the amplitudes of the local magnetic moments. The non-collinearity gives rise to an anomalous volume dependence of the binding energy, and explains other peculiarities of Invar systems.

Chitharanjan A Hegde - One of the best experts on this subject based on the ideXlab platform.

  • magnetic property and corrosion resistance of electrodeposited nanocrystalline iron nickel Alloys
    Applied Surface Science, 2012
    Co-Authors: G P Pavithra, Chitharanjan A Hegde
    Abstract:

    Abstract In the present investigation we have galvanostatically synthesized nanocrystalline Fe–Ni Alloys on copper substrate. The effect of current density (c.d.) on composition, surface morphology and phase structure were studied for explaining the magnetic and electrochemical properties of the nanocrystalline alloy. The bath found to exhibit the preferential deposition of less noble Fe than Ni, and at no conditions of c.d., the deposition has changed from anomalous to normal type. Surface morphology and structural characteristics of the deposits were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. As composition of the alloy varied, consequent to the current density a change of body centered cubic structure (bcc) to face centered cubic structure (fcc) was observed for nanocrystalline materials. Finally, the conditions responsible for peak magnetic property and corrosion resistance were optimized. Factors responsible for improved functional properties were explained in terms of surface morphology and crystalline grain size of the coatings.