Ultrasound-assisted electroless deposition of Co-P hard magnetic films

Abstract

We present here the growth kinetics and characterization of Co-P magnetic films deposited electrolessly from alkaline baths onto activated copper substrates with and without the assistance of an ultrasonic agitation (UsA). Regular electroless deposition was conducted at 60 °C, 68 °C, 76 °C and 84 °C, respectively. A 53 kHz ultrasound with an output power of 162 watt was adopted for a desired deposition rate at 44 °C, 52 °C and 60 °C, respectively. The deposition rates, for films deposited at 60 °C, are 53 and 21 nm/min, respectively, with and without UsA. The autocatalytic reaction follows a first order reaction mechanism for both regular and UsA-electroless deposition methods. Arrhenius analyses indicate that the activation energies are 34.7 kJ/mol and 83.8 kJ/mol, respectively, with and without UsA. Comparing films deposited to the same thickness of 1.1 μm, the films deposited with UsA at 60 °C exhibit magnetic properties comparable to those films deposited without ultrasound at temperatures higher than 80 °C. In the former case, the best in-plane hard magnetic properties are intrinsic coercivity (Hci) 620 Oe and residual magnetization (Mr) 114 emu/g. The perpendicular ones are Hci 1280 Oe and Mr 43 emu/g. The relationships among depositing reaction kinetics, film composition, morphology and crystal structure well explain the observed evolution of magnetic and mechanical properties. Comparing with the regular electroless deposition, UsA facilitates maintaining Co content, smoothening morphology and forming nano-crystalline grains, resulting in enhanced Hci, Mr and hardness at relatively lower depositing temperatures. The hard magnetic Co-P films produced by UsA-electroless deposition are promising for various applications such as micro-electromechanical systems (MEMS) and recording media.