Magnetic Cu–Ni (core–shell) nanoparticles in a one-pot reaction under microwave irradiation

Abstract

We successfully prepared face-centered cubic (fcc) Cu–Ni (core–shell) nanoparticles by intramolecular reduction of formate complexes of Cu²⁺ and Ni²⁺ with long-chain amine ligands in a one-pot reaction within an extremely short time realized only under microwave irradiation. Observation by an HAADF-STEM technique showed that the nanostructure in one particle consisted of a Ni-rich shell and a Cu-rich core. Cu₄Ni₆ nanoparticles with an average size of 11.7 nm were comprised of a Cu core with a diameter of ca. 6.0 nm, a Ni shell ca. 1.6 nm thick and a 0.9 nm thick interlayer of mixed Cu–Ni alloy between the Cu core and the Ni shell. Both the oxidation characteristics and the magnetic properties were dramatically affected by the molar ratios of Cu : Ni in the Cu–Ni nanoparticles. The magnetization of Cu₃Ni₇ and Cu₄Ni₆ comprised of a diamagnetic Cu-rich core, ferromagnetic Ni-rich shell and antiferromagnetic NiO-rich layer on the particle surface showed an exchange bias (209 and 143 Oe, respectively).