Microstructural evolution and magnetic properties of ultrafine solute-atom particles formed in a Cu₇₅–Ni₂₀–Fe₅ alloy on isothermal annealing

Abstract

Microstructural features strongly affect magnetism in nano-granular magnetic materials. In the present work we have investigated the relationship between the magnetic properties and the self-organized microstructure formed in a Cu75–Ni20–Fe5 alloy comprising ferromagnetic elements and copper atoms. High resolution transmission electron microscopy (HRTEM) observations showed that on isothermal annealing at 873 K, nano-scale solute (Fe,Ni)-rich clusters initially formed with a random distribution in the Cu-rich matrix. Superconducting quantum interference device (SQUID) measurements revealed that these ultrafine solute clusters exhibited super-spinglass and superparamagnetic states. On further isothermal annealing the precipitates evolved to cubic or rectangular ferromagnetic particles and aligned along the 〈100〉 directions of the copper-rich matrix. Electron energy-band calculations based on the first-principle Korringa–Kohn–Rostocker (KKR) method were also implemented to investigate both the electronic structure and the magnetic properties of the alloy. Inputting compositions obtained experimentally by scanning transmission electron microscopy–electron dispersive X-ray spectroscopy (STEM–EDS) analysis, the KKR calculation confirmed that ferromagnetic precipitates (of moment 1.07μB per atom) formed after annealing for 2 × 104 min. Magneto-thermogravimetric (MTG) analysis determined with high sensitivity the Curie temperatures and magnetic susceptibility above room temperature of samples containing nano-scale ferromagnetic particles.

Linear arrangements of nano-scale ferromagnetic particles spontaneously formed in a copper-base Cu–Ni–Co alloy

“…In previous studies, precipitation phenomena in Cu-Co [24] and Cu-Fe [25] alloys have been reported as typical examples of Ostwald ripening, and this interpretation has been accepted widely. However, the detailed features of precipitation in Cu-Ni-Co alloys, as described here and in [16], or in Cu-Ni-Fe [17][18][19] alloys, are not in accord with what is expected in normal alloys. In this work, we have shown that precipitation in a Cu-Ni-Co alloy may be understood by taking magnetic interaction into account.…”

“…However, these calculations assume the ambient temperature to be zero Kelvin, and it is possible that precipitates are not ferromagnetic at the annealing temperature. For this reason we measured the Curie temperature of the alloy specimens using a MTG balance, as described in our earlier paper on Cu-Ni-Fe alloys [19]. The MTG balance used in the experiments was a modified TG-DTA apparatus with a ferrite magnet, which produced a magnetic field in the vicinity of the sample of approximately 46 Oe.…”

“…Our own team has also conducted investigations of the relationships between microstructures and magnetic properties of magnetic particles formed in various bulk alloys including Cu-Co [15,16], Cu-Ni-Co [16], Cu-Fe [17], Cu-Ni-Fe [17][18][19], and Cu-Fe-Co [20]. The study of homogeneous bulk materials has enabled us to explore in detail the evolution of microstructures on annealing, including the morphology, composition, sizes, shapes and spatial distribution of the particles, and the influence of these parameters on magnetic properties.…”

Magnetization Characteristics of Oriented Single-Crystalline NiFe-Cu Nanocubes Precipitated in a Cu-Rich Matrix

“…Thereafter, the samples contained in capsules were subjected to an aging treatment: they were heated at 873 K for 1000 min in an electric furnace. Details of the sample preparation can be found in [ 20 , 21 ] and the articles cited therein. The sample for measurement was cut into a cube with side lengths of 2 mm and a mass of 76.1 mg.…”

“…The nanocubes were aggregated and formed rectangular blocks that were aligned in the <100> direction of the matrix. Figure 1 , which shows the electron diffraction pattern of the selected area of the sample, indicates that both the matrix and the nanocubes crystallized with FCC structures, and that their crystal orientations were identical [ 21 ]. The electron back-scattering diffraction inverse pole figure map obtained revealed that the sample was single crystalline, and its crystal direction covered an area of approximately 2 mm × 2 mm [ 20 ].…”