Effect of NiFe layer thickness on properties of NiFe/Cu superlattices electrodeposited on titanium substrate

Abstract

NiFe/Cu superlattices having different ferromagnetic NiFe layer thicknesses were grown on polycrystalline titanium substrate from a solution containing nickel, iron and copper ions under potentiostatic control. The NiFe layer thickness of the superlattices was changed from 1.5 to 8 nm while the Cu layer thickness was kept constant at 1 nm. The energy dispersive X-ray analysis revealed that, as the NiFe layer thickness increases, the Ni content of the samples increases, the Cu content decreases and Fe content decreases slightly. NiFe/Cu superlattices were polycrystalline face centred cubic (fcc) structure with NiFe and Cu layers adopting the fcc structure due to the low amount of Fe content in the deposits. The crystal orientation of the superlattices was obtained as {111}. The lattice parameters were calculated and slightly decrease from 0.36012 to 0.35382 nm with increase in the NiFe layer thickness. According to the Scanning Electron Microscopy images, when the NiFe layer thickness increases, the cauliflower region becomes less and then the granular-like regions were seen on the surface of the samples. And, the magnetic measurements showed that the saturation magnetization gradually increased from 12.9 to 291.3 emu/cm(3) with increasing NiFe layer thickness from 1.5 to 8 nm, confirming the increase of the Ni contents and decrease of the Cu amount in the superlattices. Also, the coercivities ranging from 25.1 to 63.2 Oe are between the soft and hard magnetic properties. The superlattices having NiFe layer thickness less than 5 nm showed giant magnetoresistance (GMR) while the superlattices having greater NiFe layer thicknesses showed aniotropic magnetoresistance. The GMR values of up to 2% were observed for NiFe/Cu superlattices deposited on titanium substrate. It is seen that this material may have the potential applications in sensor and recording media.