Transition to Linear Domain Walls in Nanoconstrictions

Domain walls in nanoconstrictions are investigated with a focus on thermal properties. In general, the magnetization component perpendicular to the easy axis which in a domain wall usually occurs has a value different from the easy-axis bulk magnetization value with a separate phase transition at a critical temperature below the Curie temperature. Since this effect is the more pronounced the smaller the domain wall width is, we investigate it especially in domain walls with a confined geometry, using analytical arguments, mean-field theory, and Monte Carlo simulations. Our findings may contribute to the understanding of magnetoresistive effects in domain walls with sizes of only a few atomic layers, as, e.g., in nanocontacts or nanoconstrictions.

Figure 1

Sketch of the wall geometry. The magnetization of the first and the last plane are antiparallel along the easy axis. The magnetization rotates in a plane via the hard axis.

Figure 2

Ground state easy- and hard-axis magnetization profiles for constrained walls. Data points are from low temperature MF calculations; solid lines correspond to Eq. (2). $D/J=0.003$.

Figure 3

Easy- and hard-axis magnetization profiles in MF approximation for two different temperatures. $D/J=0.03$.

Figure 4

Temperature dependence of easy- and hard-axis order parameters and (reduced) inverse domain wall width from MF calculations. $L=50a$, $D/J=0.3$.

Figure 5

Anisotropy dependence of the two critical temperatures $T_c$ and $T_h$. Data points are from MF calculations as in Fig. 4, solid lines from Eq. (6).

Figure 6

Dependence of the critical temperature $T_h$ from the size of the constrained domain wall. Comparison of MC data, MF calculations, and Eq. (7) (solid line). The dashed line is a guide to the eye.