Structural and magnetic tunability of Co/Cu multilayer nanowires induced by electrolyte acidity and spacer layer thickness

Abstract

Co/Cu multilayer nanowires (MNWs) were ac pulsed electrodeposited into the 50 nm diameter nanopores of anodic aluminum oxide (AAO) templates in 2.5, 3.8 and 5.25 pH values using the single bath technique. In each acidity, thickness of the Co magnetic layers (tCo) was kept constant (∼45 nm) and that of the non-magnetic Cu layers (tCu) was changed (3, 15, 32, 65, 160 and 260 nm) by adjustment of pulse numbers. Structural and magnetic properties of the samples were studied by X-ray diffraction (XRD) patterns, transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), hysteresis loops and first order reversal curve (FORC) diagrams. TEM images confirm the formation of multilayer structure and uniformity in thickness of the layers. XRD patterns show strong effect of the acidity and Cu-layer thickness on crystallographic characteristics. The acidity along with Cu-layer thickness caused the c-axis direction to change from parallel to perpendicular to the wires axis. A strong relation between crystalline features as preferred orientation and magnetic properties of the samples was also observed by hysteresis loops and FORC diagrams. As shown, both the acidity and tCu affect magnetic response of the magnetic system. FORC diagrams also showed that magnetostatic interactions between the magnetic layers significantly decrease with the increase in tCu, regardless of the electrolyte acidity. The coercivity distribution was also seen to vary through both crystalline structure and magnetostatic interactions.