Magnetic Reversal on Vicinal Surfaces

We present a theoretical study of in-plane magnetization reversal for vicinal ultrathin films using a one-dimensional micromagnetic model with nearest-neighbor exchange, four-fold anisotropy at all sites, and two-fold anisotropy at step edges. A detailed "phase diagram" is presented that catalogs the possible shapes of hysteresis loops and reversal mechanisms as a function of step anisotropy strength and vicinal terrace length. The steps generically nucleate magnetization reversal and pin the motion of domain walls. No sharp transition separates the cases of reversal by coherent rotation and reversal by depinning of a ninety degree domain wall from the steps. Comparison to experiment is made when appropriate.Comment: 12 pages, 8 figure

Hyperfine splitting and isotope shift in the atomic D2D_2 line of 22,23^{22,23}Na and the quadrupole moment of 22^{22}Na

The hyperfine structure of the $D_2$ optical line in $^{22}$Na and $^{23}$Na has been investigated using high resolution laser spectroscopy of a well-collimated atomic beam. The hyperfine splitting constants $A$ and $B$ for the excited $3p$ $^2P_{3/2}$ level for both investigated sodium isotopes have been obtained. They are as follows: $A(22) = 7.31(4)$ MHz, $B(22) = 4.71(28)$ MHz, $A(23) = 18.572(24)$ MHz, $B(23) = 2.723(55)$ MHz. With this data, using the high precision MCHF calculations for the electric field gradient at the nucleus, the electric quadrupole moment of $^{22}$Na has been deduced: $Q_s(22) = + 0.185(11)$ b. The sign of $Q_s(22)$, determined for the first time, indicates a prolate nuclear deformation. A precise value of the isotope shift $^{22,23}$Na in the $D_2$ line has also been obtained