Effect of Current Density on the Microstructure and Magnetic Properties of Electrodeposited Co₂FeSn Heusler Alloy

Abstract

Synthesis of Co 2 FeSn Heusler alloy using a simple and low-cost electrodeposition method is reported for the first time. The effect of deposition current density on crystal structure, chemical composition, morphology and magnetic properties of the samples was studied. The electrodeposited Co 2 FeSn alloy showed a nanocrystalline structure. Magnetic measurement reveals that the obtained Co 2 FeSn are soft magnetic at room temperature with the coercivity of 32 Oe. The saturation magnetic moment of the electrodeposited Co 2 FeSn alloy at 5 K is estimated to be 4.5 μ B /f.u. The relationship between the microstructure and magnetic properties of the samples was discussed.The Co 2 YZ (Y = transition metals, Z = main group element) Heusler compounds are of special interest for applications as they exhibit a large saturation magnetization and high value of Curie temperature. They are a remarkable class of magnetic materials that hold the greatest potential to achieve half-metallicity at room temperature and are also ideal for spintronics. 1,2 Up to now, a large number of Co 2 YZ compounds have been synthesized and their structures and physical properties have been investigated. 3 Various methods include magnetron sputtering, 4,5 molecular beam epitaxy, 6 arc melting 7 and ballmilling 8 are commonly used to prepare the Heusler alloys.Recently, there has been a renaissance of the electrochemical deposition method for the synthesis of compositionally modulated alloys, because the electrodeposition process is cheap and is possible for industrial production. 9-11 The advantages of electrodeposition over physical deposition methods are numerous: no need of vacuum equipment, easier handling, higher deposition rates. 12 Moreover, electrodeposition has the potential to yield amorphous and microcrystalline alloys which cannot be obtained from the corresponding thermally produced alloys of the same chemical composition. 13 Regretfully, up to now, there are no studies on the synthesis of Co 2 YZ Heusler alloys using the electrodeposition method.Co 2 FeSn is a cheap Heusler alloy and is predicted to have considerably large magnetic moment according to Slater-Pauling behavior. 14,15 In Co 2 YZ Heusler compounds with the cubic L2 1 ordered structure, Co atoms occupy the Wyckoff position 8c (1/4, 1/4, 1/4), Y and Z atoms are located at 4a (0, 0, 0) and 4b (1/2, 1/2, 1/2), respectively. Depending on site exchangeability, various types of site disorders have been identified: if all atomic sites are equivalent, the Co 2 YZ Heusler alloy will show an A2-type disorder [body-centered cubic (bcc) lattice]; while if only Y and Z atoms are exchangeable, the 4a and 4b positions become equivalent, the Co 2 YZ Heusler alloy will show a B2 ordered structure (simple cubic lattice). 16 In our previous work, Heusler Co 2 FeSn nanoparticles in a B2-type cubic structure have been synthesized by using a solution reduction method. 17 The obtained Heusler Co 2 FeSn nanoparticles were ferromagnetic at room temperature and showed a saturation magnetization (...

B2 long-range order in mechanically alloyed Fe53.3−0.6x Co46.7−0.4x Sn x (2 ≤ x ≤ 26) annealed at moderate temperatures

“…Three types of alloy structures have been reported according to the preparation method, bcc (A2), B2, and L2 1 . Ternary Fe-Co-Sn alloys were prepared by electrodeposition: as-prepared alloys, among which Co 2 FeSn and alloys whose compositions are close to those investigated here (see ''Nanocrystalline mechanically alloyed p-Fe 50-y/2 Co 50-y/2 Sn y '' section), were established to be bcc (A2) [12,13]. Small amounts of Co 3 Sn 2 were observed to form according to the current densities [12].…”

“…Ternary Fe-Co-Sn alloys were prepared by electrodeposition: as-prepared alloys, among which Co 2 FeSn and alloys whose compositions are close to those investigated here (see ''Nanocrystalline mechanically alloyed p-Fe 50-y/2 Co 50-y/2 Sn y '' section), were established to be bcc (A2) [12,13]. Small amounts of Co 3 Sn 2 were observed to form according to the current densities [12]. Li et al used a reduction method of metal chlorides and sulfate, with sodium hypophosphite as a reducing agent, to prepare nanoparticles of B2 Co 2 FeSn [14].…”

Preparation of Co2FeSn Heusler alloys by electrodeposition method

“…As the deposition potential decreases, the H c decreases and reaches its minimum (H c ∼ 60 Oe) at −1.5 V, then increased at below −3.6 V. In general, the coercivity is affected by many factors, such as defects, grain size, and Co content in the films. 6,9 In our case, using XRD data in Fig. 4, the grain size of the stoichiometric samples is smaller than that of non-stoichiometric one according to Scherrer equation.…”

“…5 However, there are only a few reports on the electrodeposition methods for the Heusler alloys and their related systems. 6 Electrodeposition is a non-equilibrium process as well as vacuum-based physical deposition processes like sputtering, electron beam evaporation, and chemical vapor deposition. Consequently, we expect that thermodynamically unstable phase such as Co 2 FeSn can be synthesized.…”

“…The solution was composed of CoSO 4 (0.075 M), FeSO 4 (0.05 M), and SnSO 4 (0.0083 M) on the basis of the earlier reports by Chisholm et al 10 and Duan and Kou. 6 Other additives are sodium gluconate (NaC 6 H 11 O 7 ) (120 g/l) for complexing agent, peptone (0.1 g/l) to make a dense glossy surface, ascorbic acid (2 g/l) for stabilizer, and borbic acid (0.3 M) for buffering. NaCl (0.3 M) was added in the electrolytes to improve the electronic conductivity of the bath.…”