Journal of Magnetism and Magnetic Materials 320 (2008) e819–e822 High-frequency permeability of electroplated CoNiFe and CoNiFe–C alloys Fernando M.F. Rhen, Paul McCloskey, Terence O’Donnell, Saibal Roy à Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland Available online 26 April 2008 Abstract We have investigated CoNiFe and CoNiFe–C electrodeposited by pulse reverse plating (PRP) and direct current (DC) techniques. CoNiFe(PRP) films with composition Co 59.4 Fe 27.7 Ni 12.8 show coercivity of 95 A m 1 (1.2 Oe) and magnetization saturation flux (m 0 M s ) of 1.8 T. Resistivity of CoNiFe (PRP) is about 24 mO cm and permeability remains almost constant m r 0 475 up to 30 MHz with a quality factor (Q) larger than 10. Additionally, the permeability spectra analysis shows that CoNiFe exhibits a classical eddy current loss at zero bias field and ferromagnetic resonance (FMR) when biased with 0.05 T. Furthermore, a crossover between eddy current and FMR loss is observed for CoNiFe-PRP when baised with 0.05 T. DC and PRP plated CoNiFe–C, which have resistivity and permeability of 85, 38 mO cm, m r 0 ¼ 165 and 35 with Q410 up to 320 MHz, respectively, showed only ferromagnetic resonance losses. The ferromagnetic resonance peaks in CoNiFe and CoNiFe–C are broad and resembles a Gaussian distribution of FMR frequencies. The incorporation of C to CoNiFe reduces eddy current loss, but also reduces the FMR frequency. r 2008 Elsevier B.V. All rights reserved. PACS: 91.60.Pn; 61.66.Dk Keywords: High moment; Electroplated CoNiFe; High-frequency permeability 1. Introduction The research in high moment alloys has mostly been driven by application in recording media. The basic requirements for this application are high magnetization saturation and low coercivity. High saturation magnetiza- tion is required to write magnetic memory elements with high coercivity resulting in higher information density. Lower coercivity is correlated with smaller magnetic losses allowing operation at higher frequency. The most attrac- tive alloy investigated to date is CoNiFe [1]. Coercivities smaller than 159 A m 1 (2 Oe) with saturation magnetiza- tion of 2.1 T have been reported [2,3]. Pulse plating has been applied for the preparation of high moment CoNiFe [4–6] and FeNi [7]. The combination of pulse plating and additives, such as saccharin shows improvement on morphology by reducing stress in electro- plated materials [4]. The incorporation of sulfur [8,9] and carbon [10] into the deposits increase the resistivity, but reduce the saturation magnetization. Pulse reverse plated (PRP) CoNiFe combined with additives was studied by Rasmussen et al. [11]. They prepared films with coercivity of about 510 A m 1 (6.5 Oe) and saturation magnetization of 1.7 T. Here we study the static and high-frequency magnetic properties of pulse reverse plated (PRP) CoNiFe in absence of additives and then compare with DC and PRP plated CoNiFe–C. 2. Experimental CoNiFe and CoNiFe-C were electrodeposited from electrolyte described in Table 1. Galvanic pulse reverse plating and DC plating were carried out using an averaged current density of 16 mA cm 2 . The pulse reverse plating waveform has a duty cycle of 90% and ratio of reverse/ forward current amplitude pulse of 4. Plating was carried out in open atmosphere with strong mechanical stirring. Films were electrodeposited from fresh solutions on Si substrate with a 200 nm sputtered Cu seed layer cut into ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2008.04.133 à Corresponding author. Tel.: +353 21 490 4331; fax: +353 21 427 0271. E-mail address: saibal.roy@tyndall.ie (S. Roy).