Experimental observation of switching in ferromagnetic nanoscale double disks

Abstract

We investigated a system of two overlapping ferromagnetic permalloy disks, called a hysteron. For sufficiently small disk diameters the hysteron contains only one vortex which is displaced off the center of the disk hosting it. By swapping the vortex from one side of the disk to the other via an in-plane magnetic field, the magnetization in the appended disk is reversed. The magnetization reversal process based on these off-center magnetic vortex states was theoretically found to have low switching fields, as magnetization reversal does not require wall nucleation. Here we investigate hysterons experimentally by studying magnetization reversal and configuration by means of Lorentz transmission electron microscopy and electron holography. For the smallest hysterons with individual disk diameters below ϳ200 nm we found the peculiar switching scheme suggested recently.

Phase diagram of magnetic nanodisks measured by scanning electron microscopy with polarization analysis

“…However, the previous MFM imaging studies could not determine the nanodisk phase diagram near the triple point since those measurements were often limited to perpendicularly magnetized nanodisks 23,26 or magnetic disks larger than 100 nm in diameter. 25 Lorentz and holographic transmission electron microscopy methods also provide an incomplete picture since they are limited to imaging magnetization components perpendicular to the electron beam, 27,28 and these studies have also focused on larger nanodisks. 29 Determining the phase diagram of magnetic nanodisks has been a challenge for magnetic microscopy since it requires a noninvasive measurement of both the in-plane and out-of-plane magnetization components with high resolution.…”

Arrangement effects of triangular defects on magnetization reversal process in a permalloy dot

“…In this respect, magnetic vortex structures which are frequently observed in submicron-sized ferromagnetic particles may play an important role [6][7][8][9][10][11][12]. The vortex nucleation and annihilation mechanisms have been widely investigated for nanodots with different shapes, both experimentally and theoretically [13][14][15][16][17][18]. The characteristic intermediate states appear during the switching process which evolve from onion state to vortex state include C, S and W state [19,20].…”

“…The characteristic intermediate states appear during the switching process which evolve from onion state to vortex state include C, S and W state [19,20]. Recently, there are some studies focus on the intermediate states in circular and square elements that investigate their size effects and the states of minimum energy as functions of the thickness, edge length, and material parameters [20][21][22][23][24][25]. However, no internal mechanism was reported to be able to induce the change of the intermediate state, which could influence the nucleation process of the vortex.…”

Magnetic Vortices in Ferromagnetic Nanodots

“…The coupling between rotations of vortices in double disk structures was considered in [44][45][46]. The coupling between cores was discussed in [45]. It was mentioned that the most significant consequences of this interaction are the reduction of the resonance frequency of coupled modes and asymmetry of the spectrum.…”

“…An understanding of the dynamic interaction between vortex cores and between magnetic nanodot arrays is very important. The coupling between rotations of vortices in double disk structures was considered in [44][45][46]. The coupling between cores was discussed in [45].…”