A study of the magnetic properties of iron nanowires with varying aspect ratios by micromagnetic simulation

Micromagnetics is a powerful continuum theory that is widely used to calculate spin configurations in ferromagnetic materials. This research micromagnetic modeled iron nanowires with various aspect ratios between the diameter (9, 12.6, 36, and 54 nm) and length 200 nm of the wire. Analyzing the hysteresis loops revealed that the coercive field 1.2 T of Fe nanowires with diameter of 9 nm. Introduction: Magnetic nanowires possess unique magnetic properties, making them ideal for advanced devices. Studies have been conducted on nanowires modeled with micromagnetic simulation of Ni, Fe, Co, and FeCo [1, 2]. Two categories of studies exist about nanowires: the fabrication of magnetic nanowires and the use of micromagnetic simulations to understand processes [3, 4]. Our research has important implications for designing magnetic nanowire-based devices and introduces micromagnetic simulation as a valuable tool for studying ferromagnetic materials. Simulation description: This study used ubermag software and finite difference method (FDM) for simulation [5, 6]. Nanowire diameter was (9, 12.6, 36, and 54 nm), while length was 200 nm. Cell lengths are dx = dy = 1.8 nm and dz = 2.5 nm. BCC iron material properties were used [7]. Magnetic field was varied from -1.5 T to +1.5 T to simulate a hysteresis loop. Fig. 1 illustrates a schematic of the discretization cell and nanowire. Figure 1. Schematic of the geometry of (a). a cell, (b). a nanowire. Result and discussion: Fig. 2 displays hysteresis curves with varying diameters. Coercive field decreases as diameter increases, consistent with other studies [7, 8]. Aspect ratio plays a crucial role in nanowire magnetization behavior; decreasing aspect ratio results in a lower coercivity field required for magnetization reversal. This means it becomes harder to reverse magnetization in nanowires with higher aspect ratios due to the anisotropy energy. In other words, coercivity decreases due to the competition of magnetic anisotropy and creating a domain wall. Another result, if the aspect ratio of the nanowires exceeds approximately 11, the hysteresis loop shape appears similar; indicating that any decrease in D beyond this point would yield the same result for reversal magnetization. As a result, the impact of shape anisotropy on nanowires with an aspect ratio greater than 10 remains constant. Figure 2- Hysteresis loops for an individual nanowire with L=200 nm and D values of , (a) 9 nm, (b) 12.6 nm, (c) 36 nm, and (d) 54 nm. Fig. 3 shows the magnetic moment variations for different diameters of nanowires, mostly aligned along their long axis. Fig. 3 shows that the magnetization distribution differs between the top and center of the nanowire. It is also evident that the hysteresis curve of magnetization averaged over the nanowire. Fig. 4 displays the 3D distribution of static magnetic moments, revealing a tilt of the magnetic moment at the edge of the nanowire. The phenomenon of moment rotation on top of nanowires has been observed in various other studies too [1]. Figure 3- The magnetization vector field is observed from above in the top z-plane and the x-y-plane, (a) 9 nm, and (b) 54 nm. Figure 4- The distributions of static magnetic moments for the nanowire with diameters of 54 nm. Conclusion: Results indicate that the aspect ratio strongly influences the magnetization behavior of the nanowire and that the coercivity field for magnetization reversal decreases with decreasing aspect ratio for nanowires. This decrease in coercivity may be attributed to the use of domain wall motion in nanowires with an aspect ratio of less than 10, facilitating magnetization reversal and competition of magnetic anisotropy.