Spontaneous Microstructural Evolution and Magnetic Properties of Nano-Scale Particles Comprising Ferromagnetic Element Atoms in Cu-Ni-Fe and Cu-Ni-Co Alloys

Abstract

Nano-scale granular magnetic material is a core component in next-generation recording devices. We investigated the influences of element species and composition of ferromagnetic atoms in copper-nickel base nanogranular magnetic materials. In this work, the authors focused on how microstructural evolution and magnetic properties are correlated in Cu-20at%Ni, Cu-15at%Ni-5at%Co and Cu-15at%Ni-5at%Fe alloys. We used Magneto-thermogravimetry (MTG), superconducting quantum interference device (SQUID) magnetometry and first-principles calculations based on the method of Koster-Korringa-Rostker (KKR) with the Coherent Potential Approximation (CPA) in order to investigate magnetic properties. Transmission electron microscope (TEM) observations revealed that ferromagnetic element atoms were precipitated with annealing at 973K, but microstructures were changed, depending on the combination and composition of the solute atoms. The magnetic property measurements and first-principles calculations have confirmed that magnetic precipitates are responsible for the magnetic properties of the Cu-Ni-Co and Cu-Ni-Fe alloys.

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

“…From these analyses, we concluded that the precipitated nanocubes of Cu 21.2 Ni 51.4 Fe 27.4 (hereafter denoted as NiFe-Cu nanocubes) are ferromagnetic, while the Cu-rich matrix is substantially nonmagnetic [ 22 ]. We also confirmed the nonmagnetic nature of the as-quenched CuNi alloy from its magnetization curve obtained at 5 K with a magnetic field up to 2390 kA/m, using a SQUID magnetometer [ 23 ]. According to the phase diagram and Curie temperature variation of CuNiFe alloys reported in earlier publications [ 24 ], Cu 21.2 Ni 51.4 Fe 27.4 and Cu 80.9 Ni 16.6 Fe 2.5 alloys are stable in the crystal structure of FCC, and their Curie temperatures are approximately 700 K and considerably lower than room temperature, respectively.…”