Induced Codeposition of Sm–Co Amorphous Films in Urea Melt and Their Magnetism

Abstract

The electroreduction of Co͑II͒ and Co͑II͒ + Sm͑III͒ in urea-acetamide-NaBr-MCl x melts were investigated by cyclic volatmmetry and chronoamperometry. The reduction of Co͑II͒ is an irreversible process. Sm͑III͒ cannot be reduced alone, but Sm-Co can be codeposited by induced deposition. The mechanism may involve a polynuclear complex containing Co͑II͒ and Sm͑III͒. An amorphous Sm-Co film comprised of nanoagglomerates has been synthesized. SEM shows that most of the agglomerates fall within a size range of 20-35 nm with a few agglomerates in the 50-90 nm range. The Sm content in the films varies from 7.9 to 79.16 wt % with the applied potential and the molar ratio of Sm͑III͒/Co͑II͒ in melt. The film could be crystallized by heattreatment at 900°C. Large crystal grains appeared after heat-treatment and their phase was confirmed as Sm 2 Co 17 . In addition, crystalline nanoparticles with the size of 10 nm were found on these large crystal grains. The magnetic properties of the Sm-Co films were determined using hysteresis loops, the coercive field H c of Sm ͑79.16 wt %͒-Co amorphous film is 2300 Oe at 5 K; and the remanent magnetization M R and the saturation magnetization M S are 0.536 and 1.429 emu g −1 , respectively.Rare earth ͑RE͒-transition metal ͑TM͒ alloys have excellent magnetic, optical, and electric properties and have been used to fabricate functional materials. Sm-Co alloys are widely used in permanent magnet applications because of their high-performance intrinsic magnetic properties such as very high Curie temperatures, high anisotropy fields, and relatively high saturation magnetizations. SmCo 5 alloy with the anisotropy larger than 10 8 erg cm −3 is expected to be a potential material for high-density recording media. 1 Permanent magnet materials based on Sm 2 Co 17 compound are the best candidates among all known materials for high-temperature applications. 2 Since the 1990s great progress has been made in the field of magnetic materials through the development of amorphous and nanocrystalline magnetic alloys, for example, the Finemet alloy and Nanoperm alloy which have proven to be excellent soft magnetic materials. 3,4 The amorphous RE-TM alloys, which are generally ferrimagnetic, have been intensively studied because of their potential practical applications. They can be used as magneto-optic recording media 5 because the crystallographic structure of amorphous alloys consists of a random array of atoms with very short-range correlations, leading to randomly distributed local anisotropy directions. 6 An amorphous phase may be used as a precursor to prepare a nanocrystalline structure upon crystallization. 7,8 When a certain amount of nanocrystalline phase is grown within the amorphous phase by annealing, the nanocomposite exhibits some peculiar characteristics which interest both materials scientists and engineers. 9,10 For instance, the exchange-spring magnet is prepared by the novel nanoassembly of known magnetic materials to create a composite with new and improved properties. They are based on...

Electrodeposition of RE–TM (RE=La, Sm, Gd; TM=Fe, Co, Ni) films and magnetic properties in urea melt

“…From the figure, it is found that the RE contents of the RE-TM films increases with decreasing applied potential (to shift negatively). At the same time, it is found that, when the potential is far away from −1.38 V, the electrode reaction becomes fast and the induced reduction of RE(III) becomes complicated, which results in the quick increase of TM(II) and the sharp decrease of RE content [28]. So, the deposition potential would be selected between −0.90 V and −1.40 V in our experiment.…”

“…From the EDS, a pure Sm-Fe film deposited from urea melt is prepared. The urea melt can remove impure water by itself owing to the hydrolyzation of urea at T > 334 K (that is, CO(NH 2 ) 2 + H 2 O = CO 2 ↑ + 2NH 3 ↑), as well as dissolve some metal oxides on the electrode surface [28], so the oxidation will not occur during the electrolysis. Of course, there may be a small amount of oxidation in the RE-TM films.…”

“…And hydrogen evolution is inevitable in the electrodeposition process, which lets the pH value shift to positive value and gives rise to the forming of the metal oxides [22]. Based on the above-mentioned reasons, a proper nonaqueous medium for metal electrodeposition, namely, a low-temperature urea molten salt has been selected [24][25][26][27][28]. The molten salt has lower eutectic point, higher conductivity, wider electrochemical window and greater solubility of metal chloride.…”

Electro-deposition of Co–La alloy films in urea melt and their performances

“…Because the content of Co of the Co-La coating is far more than that of La, so the remain cobalt in the deposit itself formed the hexagon cobalt phase (␣-Co). The structure of the IG-RE alloy prepared by electro-deposition in the melt is also amorphous phase [10,11].…”

“…Some rare earth alloys, such as Sm-Co, Tm-Co, Gd-Co, Nd-Co, etc. were successfully deposited from a urea melt salt [6][7][8][9][10][11]. The urea melt salt system has lower eutectic points below 134 • C, greater solubility of metallic salt, and a wide electrochemical window.…”