DM anisotropy in nanomagnets with in-plane magnetization

Dzyaloshinskii-Moriya anisotropy in nanomagnets with in-plane magnetization.
M. Cubukcu, J. Sampaio, K. Bouzehouane, D. Apalkov, A. V. Khvalkovskiy, V. Cros, and N. Reyren
Phys. Rev. B 93, 020401(R) (2016)

DMI-induced anisotropy orthogonal to the shape anisotropy as observed by MFM and simulations. All scale bars are 200 nm long. The arrows indicate the mean magnetization. (a) Experimental MFM phase images are displayed. The actual topographical shape is indicated by a dotted line. The MFM phase is coded in the same way as in Fig. 1. The approximate sizes are 730×260,250×100, and 160×50 nm2. (b) Corresponding simulations for different D values (all the other micromagnetic parameters fixed), using an ideal dipolar MFM tip 30 nm above the magnetic layer. The observations of the magnetization direction in ellipses of different shapes (but same materials) allow constraining the Dzyaloshinskii-Moriya interaction strength D: The shadings indicate the D values compatible with observations. In the intermediate case, the magnetization does not align along one of the axes, reflecting the minute energy difference between the states with different magnetization directions. (c) Map of the DMI and exchange energy densities (darker means lower energy density) for the case D=2.1 mJ/m2. The energy gain concentrates close to the edges.