Size-dependent magnetization switching characteristics and spin wave modes of FePt nanostructures

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 300nm. Quasi-static magnetization reversal analysis using first-order reversal curves (FORC) 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.

Resolving the Origin of Pseudo‐Single Domain Magnetic Behavior

“…With decreasing temperature, the peaks separate progressively (Figures a–d). These low‐temperature FORC diagrams resemble those associated with single vortex systems discussed above and reported by Brandt et al (), Dumas, Li, et al (), Dumas, Liu, et al (), Dumas et al (, ), Pike and Fernandez (), Winklhofer et al (), and Zhao et al (). Smirnov () recognized this possibility but dismissed it because the upper and lower peaks have significantly different magnitudes and because FORC diagrams for sample P1 lack the “butterfly” feature (Figure c) recognized by Pike and Fernandez ().…”

“…Smirnov () recognized this possibility but dismissed it because the upper and lower peaks have significantly different magnitudes and because FORC diagrams for sample P1 lack the “butterfly” feature (Figure c) recognized by Pike and Fernandez (). However, this asymmetry can be explained by different nucleation/annihilation fields (Brandt et al, ; Dumas, Li, et al, ; Dumas, Liu, et al, ; Dumas et al, ). Likewise, a “butterfly” feature will only be present when there are two distinct annihilation fields (Pike & Fernandez, ), which does not appear to be the case with the samples of Smirnov ().…”

Dynamic separation of nanomagnet sublattices by orientation of elliptical elements

“…To analyze the magnetization precession, the first 40-60 ps of the signal have been excluded and the bi-exponential background has been subtracted. 15 The Fourier spectra of the arrays with a single orientation (Figs. 1(c) and 1(d)) show different magnetization precession frequencies, at 6.6 and 3.5 GHz for parallel and perpendicular orientations relative to H ip , respectively, reflecting the different demagnetization field H d in the elliptic disks for the two orientations.…”

“…15 Briefly, a Ti:sapphire laser (Coherent MIRA 900F) and a second harmonic generator (Coherent SHG FEMTO) produce pump and probe pulse trains (pulse width $150 fs, repetition rate 76 MHz) at center wavelengths of 400 and 800 nm, respectively. The intense pump pulses (pulse energy 0.…”

Co/Pt Multilayers on Self-Organized Hexagonal Patterned Nanodots

“…Magnetic multilayers deposited on self-organized pattern formed of spherical polystyrene (PS) nanoparticles results in tilted nanostructure material. There have been extensive studies on deposition of thin films on such colloidal nanosphere arrays [14][15][16][17][18]. However, like all organic compounds, polystyrene cannot be used for the deposition of materials under high temperature or for the post-annealing of the nanomaterials, which limits the variety of nanomaterials that can be fabricated.…”