High-performance electrodeposited Co-rich CoNiReP permanent magnets

Abstract

Ferromagnetic CoNiReP films (∼3 μm in thickness) have been prepared by galvanostatic electrodeposition using direct current (DC) and reverse pulse plating (RPP) conditions. The composition, microstructure and mechanical and magnetic properties of these films strongly depend on the applied current density. The differences are particularly pronounced in the RPP-electroplated alloys, where amorphous films with 32 at% Co showing soft-magnetic behavior and large hardness values (around 9 GPa) are obtained at low cathodic current densities ( j c), whereas fully crystalline hard-ferromagnetic CoNiReP alloys containing ∼80 at% Co are produced at high j c. All DC-plated CoNiReP films exhibit crystalline microstructures with tunable grain size and texture, hard-magnetic properties (with perpendicular magnetic anisotropy) and mechanical hardness values around 7 GPa. The magnetic properties of these Co-rich CoNiReP alloys are superior to those previously reported in electroless deposited Ni-rich CoNiReP. By applying suitable current densities, films with an intrinsic coercivity of 3.5 kOe possessing a saturation magnetization around 800 emu cm −3 can be obtained from both DC and RPP deposition techniques. In addition, the films investigated in this work are thicker than electroless-plated CoNiReP alloys and can be grown in acidic pH values; thus they are suitable permanent magnetic materials for use in wirelessly actuated micro-electromechanical systems (MEMS).