Direct Observation of Internal Spin Structure of Magnetic Vortex Cores

Abstract

Thin film nanoscale elements with a curling magnetic structure (vortex) are a promising candidate for future nonvolatile data storage devices. Their properties are strongly influenced by the spin structure in the vortex core. We have used spin-polarized scanning tunneling microscopy on nanoscale iron islands to probe for the first time the internal spin structure of magnetic vortex cores. Using tips coated with a layer of antiferromagnetic chromium, we obtained images of the curling in-plane magnetization around and of the out-of-plane magnetization inside the core region. The experimental data are compared with micromagnetic simulations. The results confirm theoretical predictions that the size and the shape of the vortex core as well as its magnetic field dependence are governed by only two material parameters, the exchange stiffness and the saturation magnetization that determines the stray field energy.

Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

“…Vortices have a winding number of n = + 1 and a polarity of p = ± 1, whereas antivortices have n = − 1 (refs 1-3). Magnetic vortices are characterized by an in-plane curling magnetization (chirality) and a nanometer-sized central region with an out-of-plane magnetization (polarity) [4][5][6] . The latter is defined by a clockwise (c = 1) or counter-clockwise (c = − 1) rotation of the in-plane magnetization.…”

Self-Similar Nested Flux Closure Structures in a Tetragonal Ferroelectric

“…Of course, depolarizing fields are likely to be present at the edges of the PZN-12PT lamellae, and these should drive flux closure in some form. However, previous work on BaTiO 3 [19] and Pb(Zr,Ti)O 3 [17], has already established that the effects of depolarizing fields can be successfully accommodated by flux closure at a single length scale (mesoscale). Additional internal depolarizing fields caused within a mesoscale flux closure object should not be present.…”

Direct dynamic imaging of non-adiabatic spin torque effects

“…Simplified geometries such as disks and squares that exhibit a flux closure domain state (Landau state) can be used to circumvent some of the limitations of nanowire geometries. In a flux-closure or vortex state, the magnetization curls around in a clockwise (CW) or counter-CW (CCW) direction [12][13][14] . In square structures, the magnetization tends to follow the edges of the square to minimize the dipolar energy and diagonal Bloch walls form to reduce the quantum mechanical exchange energy.…”