Numerous studies have been conducted to develop next-generation recording technology in spintronics. Because ultrafine magneitc particles are vital components of the technology, the interplay between the microsturcture and magnetic properties has attracted attention extensively in recent years. We focused on the relationship between the microstructure and magnetic properties of Cu-Ni-X (X=Fe, Co, FeCo) alloys comprising nanogranular magnetic particles. In this work, we prepared Cu-20 at% Ni-5 at% (FeCo), Cu-20 at% Ni-5 at% Fe, Cu-20 at% Ni-5 at% Co and examined the changes of microstructure and magnetic properties associated with heat treatments and composition. To examaine microstructural evolution of the alloy specimens, we conducted transmission electron microscope observations (TEM) with the as-quenched specimens and those aged at at 773-1073 K. We also carried out magneto-thermo gravimetry (MTG) measurements, superconducting quantum interference device (SQUID) measurements, magnetoresistance (MR) measurements and first-principles calculations based on the Koster-Korringa-Rostker (KKR) method with the Coherent Potential Approximation (CPA), to investigate the magnetic properties. The present work confirmed that the microstructure significantly changed, depending on the composition and heat treatment conditions. The present work also revealed that the magnetic properties closely correlated with the microstructure of samples.

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.