Structural and magnetic properties of CoNi surface alloys

The Co100-xNix (x = 20, 40 & 60) surface alloys were deposited on Si (100) substrate by dc-magnetron sputtering technique and were investigated using Grazing Incidence X-ray Diffraction (GIXRD), X-ray reflectivity (XRR), Energy dispersive X-ray analysis (EDAX) and Magneto-Optical Kerr Effect (MOKE) measurements. GIXRD measurements suggested a compositional induced structural transition from hcp to fcc structure at x = 40. MOKE measurements indicate that the prepared alloys are soft ferromagnet with the coercive field in the range of few mT. The MOKE microscopy domain image suggests that magnetization reversal occurring through domain wall motion and coherent rotation. The angle-dependent coercivity (H-c) is numerically fitted with a two-phase model of magnetization reversal. Large anisotropy dispersion is observed for hcp Co-Ni alloys compared to fcc Co-Ni alloys. The hcp Co80Ni20 alloy has highest value of coercivity at 0 degrees but for fcc Co60Ni40 and Co40Ni60 alloys, the coercivity became highest at 120 degrees. The magnetization reversal along hard axis occurs through coherent rotation for fcc Co60Ni40 and Co40Ni60 alloys whereas in hcp Co80Ni20 alloy magnetization reversal is governed by formation of fine domains.