Abstract
We present a comprehensive investigation of the size-dependent switching characteristics and spin wave modes of FePt nanoelements. Curved nanomagnets (“caps”) are compared to flat disks of identical diameter and volume over a size range of 100 to 300 nm. Quasi-static magnetization reversal analysis using first-order reversal curves shows that spherical caps have lower vortex nucleation and annihilation fields than the flat disks. As the element diameter decreases, the reversal mechanism in the caps crosses over sooner to coherent rotation than in the disks. The magnetization dynamics are studied using optically induced small angle precession and reveal a strong size dependence that differs for the two shapes. Flat disks exhibit well-known center and edge modes at all sizes, but as the diameter of the caps increases from 100 to 300 nm, additional oscillation modes appear in agreement with dynamic micromagnetic simulations. In addition, we show that the three-dimensional curvature of the cap causes a much greater sensitivity to the applied field angle, which provides an additional way for controlling the ultrafast response of nanomagnetic elements.
Highlights
High density magnetic nanostructure arrays are of interest for applications such as magnetic random access memory[1,2,3] and patterned magnetic data storage[4,5,6]
The material deposited on the spheres forms curved magnetic “caps” which have an easy axis that is parallel to the surface of the sphere and a radial thickness dependence from center to edge
We find that large magnets of both shapes switch by vortex annihilation, but the spherical caps switch to a coherent rotation mechanism at a larger diameter than the flat disks
Summary
High density magnetic nanostructure arrays are of interest for applications such as magnetic random access memory[1,2,3] and patterned magnetic data storage[4,5,6]. A series of flat magnetic disks with identical composition, total volume, out-of-plane thickness, and in-plane diameter to the spherical caps was fabricated by standard electron beam lithography and liftoff on a planar silicon substrate with a nonmagnetic antireflective (AR) coating (Fig. 1(b)). Both isolated magnetic elements as well as nanomagnet arrays with a center-to-center distance of twice the disk diameter were fabricated. Being able to probe individual magnetic nanostructures is essential to measuring the intrinsic magnetic properties
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