Measurements of configurational anisotropy in isolated sub-micron square permalloy dots

Abstract

We measure a shape dependent anisotropy energy in isolated square permalloy dots with characteristic dimensions as small as 200 nm. The magnetization behavior is characterized using the anisotropic magnetoresistance to determine the magnetic state of the sample. The behavior is consistent with the sample adopting a quasi-single-domain magnetization with a direction determined by an anisotropy intrinsic to the square geometry. We quantify the magnitude of this anisotropy through two independent measurements and confirm the observed magnetic behavior with micromagnetic simulations.

Emergent 1/f Noise in Ensembles of Random Telegraph Noise Oscillators

“…We also examine the range of energy barriers the Van der Ziel model would predict necessary to generate 1/f noise, and compare it to our experimentally determined barrier height distribution for the individual dots [17]. There have been numerous studies of RTN and 1/f noise in semiconductors and in magnetic tunnel junctions [1,18,19], as well as observation of both 1/f and RTN in other systems [20], but an unambiguous quantification of the individual, discrete RTN signals leading to the 1/f noise spectrum has not yet been explicitly demonstrated.…”

“…Using the configurational anisotropy model developed by Endean, et. al [17], and relying on the Stoner-Wolfharth model [24], the energy landscape E(θ) is a function of both the configurational anisotropy [1,3]. The inset shows a schematic of the sample geometry; square dots (dark red) are electrically connected together by gold contacts (light green) entering the frame from the edges.…”

“…For the dots discussed here, their configurational anisotropy energies [22,23] are similar to those previously reported by Endean, et. al [17], with the easy axes of the magnetization perpendicular to the sides of the square dots. The center-to-center spacing of 1 µm is sufficient to ensure that adjacent dots do not couple either magnetostatically, or through spin-torque when a current is applied.…”

Multibit Memory Cells Based on Spin-Orbit Torque Driven Magnetization Switching of Nanomagnets with Configurational Anisotropy

“…In order to increase the memory density, one can use the fact that the anisotropy of magnets can be tailored by material and shape engineering. For example, imposing symmetry on the magnet and the introduction of certain defects have been shown to lead to interesting effects such as configurational anisotropy [1], and nucleating centers [2]. Configurational anisotropy, which is a high order form of shape anisotropy, leads to the introduction of multiple easy axes in some magnetic materials of special shapes (e.g.…”

Hysteresis and anisotropy in ultrathin Fe/Si(001) films

“…1 Overall magnetic anisotropy of ultrathin films, one of the important magnetic properties, is usually determined by the competition of shape anisotropy, magnetocrystalline anisotropy (MCA) and surface anisotropy. [2][3][4][5][6][7][8] On the other hand, domain wall displacement also plays an important role in determining the magnetization reversal. [9][10][11][12] Most studies have been focused on either coherent rotation or domain wall displacement in order to explore the detailed magnetic properties.…”