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Acta Materialia, 2016
Abstract The thermodynamic and kinetic parameters describing the chemical disordering process of ... more Abstract The thermodynamic and kinetic parameters describing the chemical disordering process of L1 0 FeNi (tetrataenite) are quantified through analysis of calorimetric data obtained from material (Fe 57 Ni 43 ) extracted from the NWA 6259 meteorite. The material presents an endotherm with peak temperatures of 800–860 K depending on heating rate and a transformation enthalpy of 4.0 ± 0.2 kJ/mol of atoms that corresponds to the L1 0 → A1 chemical order–disorder phase transformation. Using reported values of the enthalpy of mixing of the A1 phase and the enthalpy difference between the A1(γ) and the A2(α) phases of Fe, the enthalpy of formation of the L1 0 phase at the composition 43 at.% Ni constituted from Fe and Ni in their standard state is calculated as −4.4 ± 0.6 kJ/mol of atoms. These results indicate that the L1 0 FeNi phase is at the edge of enthalpic stability relative to a mixture of α-Fe and L1 2 FeNi 3 . The measured kinetic chemical-disordering transformation temperature is well above the reported order–disorder temperature of 593 K (320 °C) confirming that the disordering process is highly kinetically limited. The activation energy of chemical disordering of L1 0 FeNi (43 at% Ni) is 3.08 ± 0.07 eV/atom. Results obtained in this study are consistent with a model of one-dimensional growth of the disordered phase wherein the transformation rate is limited by the creation and migration of vacancies. Establishment of the enthalpy difference between the chemically-ordered and -disordered phases as well as determination of the activation energy for transformation provide guidance for laboratory synthesis of the L1 0 FeNi phase, which is of significant applied interest as a new advanced permanent magnet material.
... A. Bhattacharjee a , b , Corresponding Author Contact Information , E-mail The Corresponding ... more ... A. Bhattacharjee a , b , Corresponding Author Contact Information , E-mail The Corresponding Author , H. Mandal a , M. Roy c , J. Kusz d , M. Zubko d and P. Gütlich b. ... Acknowledgement. The authors acknowledge Mr. Souvik Banerjee for his assistance in SEM measurement. ...
IEEE Transactions on Applied Superconductivity, 2000
In this work we focus on the microstructural and magnetic characterization of CuNb/Nb 3 Sn wires ... more In this work we focus on the microstructural and magnetic characterization of CuNb/Nb 3 Sn wires with different architectures (design and reinforcement). The microstructural characterization was performed using scanning electron microscopy. AC magnetic susceptibility was measured with field applied both parallel and perpendicular to the wire axis. The heat treatment performed to form the A-15 superconducting phase leads to partial spheroidization followed by coarsening of the Nb filaments in the reinforcement material. The differences concerning the microstructure of the reinforcement material among the investigated wires were reflected in the broadening of the superconducting transition of Nb, more evident for a field applied parallel to the wire axis. From the magnetic data the wires were also compared in terms of the superconducting volume fraction.
IEEE Magnetics Letters, 2000
ABSTRACT Meteorites, likely the oldest source of magnetic material known to mankind, are attracti... more ABSTRACT Meteorites, likely the oldest source of magnetic material known to mankind, are attracting renewed interest in the science and engineering community. Worldwide focus is on tetrataenite, a uniaxial ferromagnetic compound with the tetragonal L1$_{0}$ crystal structure comprised of nominally equiatomic Fe–Ni that is found naturally in meteorites subjected to extraordinarily slow cooling rates, as low as 0.3 K per million years. Here, the favorable permanent magnetic properties of bulk tetrataenite derived from the meteorite NWA 6259 are quantified. The measured magnetization approaches that of Nd–Fe–B (1.42 T) and is coupled with substantial anisotropy (1.0–1.3 MJ/m 3^{3}3) that implies the prospect for realization of technologically useful coercivity. A highly robust temperature dependence of the technical magnetic properties at an elevated temperature (20–200 °C) is confirmed, with a measured temperature coefficient of coercivity of −0.005%/K, over one hundred times smaller than that of Nd–Fe–B in the same temperature range. These results quantify the extrinsic magnetic behavior of chemically ordered tetrataenite and are technologically and industrially significant in the current context of global supply chain limitations of rare-earth metals required for present-day high-performance permanent magnets that enable operation of a myriad of advanced devices and machines.
Acta Materialia, 2016
Abstract The thermodynamic and kinetic parameters describing the chemical disordering process of ... more Abstract The thermodynamic and kinetic parameters describing the chemical disordering process of L1 0 FeNi (tetrataenite) are quantified through analysis of calorimetric data obtained from material (Fe 57 Ni 43 ) extracted from the NWA 6259 meteorite. The material presents an endotherm with peak temperatures of 800–860 K depending on heating rate and a transformation enthalpy of 4.0 ± 0.2 kJ/mol of atoms that corresponds to the L1 0 → A1 chemical order–disorder phase transformation. Using reported values of the enthalpy of mixing of the A1 phase and the enthalpy difference between the A1(γ) and the A2(α) phases of Fe, the enthalpy of formation of the L1 0 phase at the composition 43 at.% Ni constituted from Fe and Ni in their standard state is calculated as −4.4 ± 0.6 kJ/mol of atoms. These results indicate that the L1 0 FeNi phase is at the edge of enthalpic stability relative to a mixture of α-Fe and L1 2 FeNi 3 . The measured kinetic chemical-disordering transformation temperature is well above the reported order–disorder temperature of 593 K (320 °C) confirming that the disordering process is highly kinetically limited. The activation energy of chemical disordering of L1 0 FeNi (43 at% Ni) is 3.08 ± 0.07 eV/atom. Results obtained in this study are consistent with a model of one-dimensional growth of the disordered phase wherein the transformation rate is limited by the creation and migration of vacancies. Establishment of the enthalpy difference between the chemically-ordered and -disordered phases as well as determination of the activation energy for transformation provide guidance for laboratory synthesis of the L1 0 FeNi phase, which is of significant applied interest as a new advanced permanent magnet material.
... A. Bhattacharjee a , b , Corresponding Author Contact Information , E-mail The Corresponding ... more ... A. Bhattacharjee a , b , Corresponding Author Contact Information , E-mail The Corresponding Author , H. Mandal a , M. Roy c , J. Kusz d , M. Zubko d and P. Gütlich b. ... Acknowledgement. The authors acknowledge Mr. Souvik Banerjee for his assistance in SEM measurement. ...
IEEE Transactions on Applied Superconductivity, 2000
In this work we focus on the microstructural and magnetic characterization of CuNb/Nb 3 Sn wires ... more In this work we focus on the microstructural and magnetic characterization of CuNb/Nb 3 Sn wires with different architectures (design and reinforcement). The microstructural characterization was performed using scanning electron microscopy. AC magnetic susceptibility was measured with field applied both parallel and perpendicular to the wire axis. The heat treatment performed to form the A-15 superconducting phase leads to partial spheroidization followed by coarsening of the Nb filaments in the reinforcement material. The differences concerning the microstructure of the reinforcement material among the investigated wires were reflected in the broadening of the superconducting transition of Nb, more evident for a field applied parallel to the wire axis. From the magnetic data the wires were also compared in terms of the superconducting volume fraction.
IEEE Magnetics Letters, 2000
ABSTRACT Meteorites, likely the oldest source of magnetic material known to mankind, are attracti... more ABSTRACT Meteorites, likely the oldest source of magnetic material known to mankind, are attracting renewed interest in the science and engineering community. Worldwide focus is on tetrataenite, a uniaxial ferromagnetic compound with the tetragonal L1$_{0}$ crystal structure comprised of nominally equiatomic Fe–Ni that is found naturally in meteorites subjected to extraordinarily slow cooling rates, as low as 0.3 K per million years. Here, the favorable permanent magnetic properties of bulk tetrataenite derived from the meteorite NWA 6259 are quantified. The measured magnetization approaches that of Nd–Fe–B (1.42 T) and is coupled with substantial anisotropy (1.0–1.3 MJ/m 3^{3}3) that implies the prospect for realization of technologically useful coercivity. A highly robust temperature dependence of the technical magnetic properties at an elevated temperature (20–200 °C) is confirmed, with a measured temperature coefficient of coercivity of −0.005%/K, over one hundred times smaller than that of Nd–Fe–B in the same temperature range. These results quantify the extrinsic magnetic behavior of chemically ordered tetrataenite and are technologically and industrially significant in the current context of global supply chain limitations of rare-earth metals required for present-day high-performance permanent magnets that enable operation of a myriad of advanced devices and machines.