Effect of Na and Cl Ions on Coercivity of Electroplated Fe-Pt Film-Magnets

Abstract

Recently, we investigated the effect of Na ion concentration in plating baths on the coercivity of L1₀ ordered Fe-Pt thick-film magnets prepared by an electroplating method and pointed out that a possibility of enhancement in the coercivity by the Na ion. In the present study, we electroplated Fe-Pt films on Cu substrates from plating baths with various concentrations of the NaCl for obtaining further evidence of the coercivity enhancement, focusing on the L1₀ ordering process of the film. From an x-ray diffraction analysis, we found that the Δ2θ, which has a diffraction peak split between (002) and (200) of the L1₀ ordered phase (fct structure), increased with increasing NaCl concentration under the same annealing conditions, and confirmed that the annealed films with large Δ2θ tend to show high coercivity. When varying the amount of NaCl in the plating bath, not only the Na ion concentration but also the Cl ion one varies, suggesting that the Cl ion also has a possibility of coercivity enhancement. In order not to vary the Cl ion concentration, we changed the reagent, which supplies the Na ions into the plating bath, from NaCl to Na₂SO₄. Consequently, the coercivity of the films for the baths with Na₂SO₄ (the Na ion) showed higher value compared with those for the baths without Na₂SO₄. From these results, we concluded that Na ion effectively works to enhance the L1₀ ordering and the coercivity for the electroplated Fe-Pt thick film-magnets.