Pulsed Aqueous Electrodeposition of Sm-Co Permanent Magnets

Abstract

Pulse current electrodeposition of Sm-Co alloys from aqueous solutions has been studied at various current densities (PCD), solution temperatures, frequency (ν), Ton and duty cycles (γ). A deposit content of 20 at %Sm was obtained at 25oC, higher than at 60oC in contrast to DC from bath of 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine at pH6. This composition is sufficient to obtain the high performance permanent magnet intermetallics, Sm2Co17 (10.5 at %) and SmCo5 (16.7 at %), by appropriate heat treatment. Increased PCD, Ton, g and decreased solution temperature or frequency increased Sm deposit content and decreased current efficiency (CE). Magnetic saturation(Ms) decreased linearly with increased Sm deposit content as DC and sputtered films. Increased Sm content resulted in significant decrease in Hc⊥ but Hc|| varied little.

Electrodeposition of Magnetic SmCo Films from Deep Eutectic Solvents and Choline Chloride-Ethylene Glycol Mixtures

“…The SmCo deposited in the glycine-containing solution shows a coercive field of 100 Oe (8.0 kA/m), higher than Co film and compatible with those reported in literature for electrodeposition from aqueous baths. [13][14][15] On the other hand, SmCo film grown in a 1ChCl:2EG solution without glycine presents a significantly higher coercive field H c = 270 Oe (21.5 A/m), in agreement with the value reported for the 1ChCl:2U system. [4][5][6] The out-of-plane direction is again a hard axis for the magnetization (Figure 6b).…”

“…Different studies on aqueous solutions report the 3[Gly]: [Co] 2+ ratio as the most suitable for codeposition of Co and Sm; a higher concentration of glycine would in fact hinder the Sm deposition. [13][14][15] The same concentration ratio has been selected also for our systems despite based on different chemistry. From the CV curve (Figure 3), it is evident the effect of glycine on the electrochemical behavior of the bath, especially for the 1ChCl:4.5EG solution.…”

“…The amount of glycine added was three times the cobalt concentration; such a ratio was reported as effective for the codeposition of SmCo in aqueous system. Wei et al [13][14][15] demonstrated how a higher glycine quantity leads to a lower Sm content in the deposit; the same [Gly]/ [Co] 2+ has been adapted to our system. Results in potentiostatic conditions are in agreement with cyclic voltammetry where a more evident reduction process was observed.…”

“…[7][8][9] In literature, works on this alloy from both waterbased 10-16 and non-aqueous solution are reported. 17 In the former case, fundamental is the employment of glycine as complexing agent as shown by Wei et al [13][14][15] However, in-plane coercivities in the order of H c|| = 100 Oe were observed with the formation of SmO, Sm(OH) 3 and Co(OH) 2 .14 These values are referred to films produced by electrodeposition, an interesting technique from the fabrication point of view but with a huge limitations in terms of compositional and purity control with respect to traditional methods as casting or sputtering through which hard SmCo magnets are obtained (H c|| ∼ kOe).This work consists in the study of different mixtures based on ethylene glycol and choline chloride (1ChCl:2EG and 1ChCl:4.5EG) in order to evaluate the effect of ChCl concentration on SmCo codeposition and its magnetic properties. Studies on the physical properties of solutions with different ChCl:HBD (Hydrogen Bond Donor) molar ratio are reported in literature.…”

“…46-79 wt% Sm, while the optimal composition for the best magnetic performances is 23-25 wt% Sm, corresponding to the Sm 2 Co 17 phase. [7][8][9] In literature, works on this alloy from both waterbased [10][11][12][13][14][15][16] and non-aqueous solution are reported. 17 In the former case, fundamental is the employment of glycine as complexing agent as shown by Wei et al [13][14][15] However, in-plane coercivities in the order of H c|| = 100 Oe were observed with the formation of SmO, Sm(OH) 3 and Co(OH) 2 .…”