Magnetic Reversal Mode Investigation of FeCo/Cu Multilayered Nanowires with Different Cu Layer Lengths

FeCo binary alloys with high saturation magnetization have been envisioned as the most promising compounds in the fabrication of solid-state devices, including hard drives. Forming multilayered nanowires (MNWs) of these alloys would allow for ultra-high density data storage by reversing spins in the 3D space. However, thorough experimental investigations into the angular magnetic properties of FeCo/Cu MNWs have not been performed yet. Here, we first electrochemically deposit FeCo/Cu MNWs into nanopores of anodic alumina membranes using a pulse method, and then comprehensively investigate their angular magnetic properties using a vibrating sample magnetometer equipped with first-order reversal curve (FORC) software. We also change the Cu layer length (LCu) in the range of 3-20 nm while keeping the FeCo layer length constant to 180 nm, and measure hysteresis loops and FORC diagrams for 0 degrees <= theta <= 90 degrees. We observe that the coercivity continuously increases with increasing theta from 0 degrees to 45 degrees when LCu <= 12 nm, and that it remains nearly constant for LCu = 20. For all LCu values, the angular dependence of hysteresis loop coercivity shows sharp reductions with increasing theta over 45 degrees, especially for theta >= 70 degrees. These events are accompanied with the appearance of perceptible single vortex states in the angular FORC diagrams and significant enhancements in magnetostatic interactions between the FeCo layers. Our evaluations based on the angular dependence of FORC coercivity peaks indicate that the magnetization reversal of the FeCo/Cu MNWs is dominated by a vortex mode, monotonically increasing the coercive field to above 3000 Oe at theta = 82.5 degrees for the lowest LCu.