Elsevier

Journal of Alloys and Compounds

Volume 611, 25 October 2014, Pages 243-248
Journal of Alloys and Compounds

Structural, morphological and magnetic characterization of electrodeposited Co–Fe–W alloys

https://doi.org/10.1016/j.jallcom.2014.05.157Get rights and content

Highlights

  • Small W additions (up to 9 at.%) to the Co35Fe65 binary system.

  • Electrodeposited Co–Fe–W alloys characterization by XRD, SEM, TEM, Mössbauer spectroscopy and magnetic measurements.

  • Production of Co–Fe–W alloys with low values of coercivity and high saturation magnetization.

  • Potential materials for applications in magnetic devices such as read/write heads and hard disks.

Abstract

Structural, morphological and magnetic characterization of electrodeposited Co–Fe–W alloys, containing small amounts of W (up to 9 at.%), were performed using X-ray diffractometry, scanning (SEM) and transmission (TEM) electron microscopy, Mössbauer spectroscopy and magnetization measurements. Electrodeposited (Co100−xFex)100−yWy films (x = 63–72 at.% Fe, y = 4–9 at.% W) were successfully produced varying the applied cathodic current density (ic) between 0.5 and 10 mA cm−2. X-ray diffraction results revealed a bcc-like structure for all studied compositions with average crystallite size ranging from 16 to 35 nm, as also confirmed by TEM results. SEM images indicated that needle-type morphology is dominant for the deposits containing lower W content (up to 4.5 at.%.), while a cauliflower-type behavior is observed for higher W content deposits. Room temperature Mössbauer spectra indicate the presence of two magnetic species for all samples; one component associated with an ordered Co–Fe–W fraction (crystalline grain core) and a magnetic disordered Co–Fe–W contribution, which can be attributed to the grain boundaries/grain surfaces. Magnetization was observed to be in the film plane along the film direction, except the sample prepared at ic = 10 mA cm−2 that is slightly canted from in- to out-of-plane geometry. Magnetic measurements show high saturation magnetization values accompanied by low coercivity ones for the electrodeposited Co–Fe–W alloys, making these alloys potential materials for applications in magnetic devices such as read/write heads and hard disks.

Introduction

In the last decades, much attention has been paid to the Co–Fe system, in particular to the Co35Fe65 alloy, due to its excellent magnetic and mechanical properties [1], [2], [3]. Such properties include high saturation magnetization (>2.4 Tesla) and Curie temperature (>1000 °C), high electric permeability and good thermal stability. Moreover, the addition of refractory elements (W, Mo or V) to the Co–Fe binary system results in improvement on hardness and corrosion resistance, enhancement of durability, and increase of thermal resistance, among others.

In this context, Co–Fe–M (M = W, Mo, V or Re) alloys have been lately produced by different techniques including sputtering, molecular beam epitaxy (MBE), physical vapor deposition (PVD), and electrodeposition etc. [4], [5], [6], [7]. Among these synthesis techniques, electrodeposition has stood out due to the following important features: cost-effectiveness, high quality deposits, production at room temperature (no need of high vacuum), and easy operating conditions. Therefore, various Co–Fe–M ternary alloys have been fabricated by electrodeposition with different purposes and applications [8], [9], [10]. The Co–Fe–M alloys, in particular the Co–Fe–W alloys, are also interesting from theoretical viewpoint because this system shows simultaneously the phenomena of anomalous [11], [12], [13] and induced co-deposition in electrodeposition processes [14], [15], [16], [17]. Specifically, the above two effects have been described in detail by Esteves et al. [18] for electrodeposited Co–Ni–Mo thin films, and recently by our group for electrodeposited Co–Ni–W alloys from a glycine-containing bath [19].

Consequently, the present work is aimed to study the structure, morphology, atomic arrangements and magnetic properties of electrodeposited Co–Fe–W alloys, with composition close to Co35Fe65 and addition of low W contents (up to 9 at.%). Several works have been reported on the electrodeposition of Co–Fe binary alloys. However, as far as we know there are only three published papers concerning electrodeposited Co–Fe–W alloys hitherto [10], [20], [21]. In general, these works were focused on high W concentration, while the present work is aimed to add small W amounts (up to 9 at.%) to the Co–Fe system. Capel et al. [10] proposed the electrodeposition of Co–W and Co–Fe–W alloys onto stainless steel as an alternative to electrodeposited hard chrome. The authors studied the hardness and wear properties, and found that the Co–W alloy containing 27 at.% W exhibits the highest hardness after heat treatment (1185 kgf mm−2), a value even higher than electrodeposited hard chromium (848 kgf mm−2). For the Co43Fe30W27 alloy, on the other hand, the measured hardness value was 838 kgf mm−2. The others two Co–Fe–W papers were published by the same group in different journals [20], [21]. Using Mössbauer spectroscopy (MS), they have been able to discussed the formation of amorphous state in Co–W–Fe alloys with W concentration higher than 14 at.% [21]. Therefore, in the present work, we focus on the structural, morphological and magnetic characterization of electrodeposited Co–Fe–W alloys for W concentration lower than 10 at.%. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Mössbauer spectroscopy and magnetic measurements have been used to analyze the structural and magnetic properties of electrodeposited Co–Fe–W films.

Section snippets

Experimental details

Co–Fe–W alloys were galvanostatically (constant current application) prepared by using an EG & G PAR M283 potentiostat/galvanostat. A Tait-type cell was used for all electrodeposition experiments. The (1 × 1) cm2 copper plates (purity > 99.99%) were used as substrate. The alloys were electrodeposited from a citrate-containing unstirred bath composed of 0.04 M Fe2(SO4)3, 0.05 M CoSO4, 0.01 M Na2WO4, 0.2 M H3BO3 and 0.2 M citrate (Na3C6H5O7). By using this particular bath formulation, Fe-rich Co–Fe alloys

Compositional analysis

Fig. 1 shows the potential vs. time (E × t) profiles used to obtain the Co–Fe–W alloys at different ic-values. Considering the fact that the passed charge was kept constant (35 C), the total time for each experiment is decreased with the increase of ic. In addition, it can be noted that when the ic-quantity is increased, the potential (E) decreases to more negative values, as would be expected. It was also possible to evaluate the thicknesses of the films and the cathodic current efficiency (CCE)

Conclusions

The structural, morphological and magnetic characterization of electrodeposited Co–Fe–W alloys, containing small contents of W (up to 9 at.%), were investigated by XRD, SEM, TEM, Mössbauer spectroscopy and magnetic measurements. By varying the applied cathodic current density (ic), electrodeposited (Co100xFex)100yWy films (x = 63–72 at.% Fe, y = 4–9 at.% W) were successfully prepared. The XRD results revealed a bcc Fe-like structure for all studied compositions with average crystallite size

Acknowledgments

The authors gratefully acknowledge financial support and scholarships from the Brazilian funding agencies CNPq, Fapesp, Prope/Unesp and Fapes. Authors also thank the Brazilian Nanotechnology National Laboratory by TEM analyses.

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