We present experimental results on magnetization reversal for a class of nanoscale magnetic films with perpendicular magnetic anisotropy and develop a model that describes a variety of related experiments.In this Inodel the sample is divided into identical single domain cells that interact through dipolar fields and a nearest-neighbor domain-wa11 interaction. Monte Carlo simulations give insights into the relationship between the macroscopic magnetic parameters and the reversal behavior and demonstrate the important role that thermal activation plays in the reversal process.Among the most exciting advances in modern condensed-matter and materials physics is the incipient development of an ability to understand and design structures with nanometer-length scales. ' These structures and the technologies based on them will be important in areas such as information storage, electronic devices, and biotechnology.As the dimensions of the fundamental building blocks or cells of magnetization, polarization, etc. , become smaller and smaller, the temporal stability of an ordered phase within the ce11 becomes of crucial importance. This problem is also intimately connected to the mechanism by which a reversal or switch of the order parameter in the cell occurs as the result of an applied stimulus.This paper is concerned with time decay and reversal phenomena in an important class of nanostructured thin films, amorphous magnetic multilayers with characteristic layer thicknesses of a few atomic diameters. Such films have considerable potential in future ultra-highdensity magneto-optic data storage systems. Magnetization reversal has been studied in a number of nanostructured thin-film and amorphous rareearth -transition-metal systems. ' These earlier measurements explicitly show that the reversal behavior in these systems tends to fall between one of two limiting categories: (a) continuous nucleation with the magnetization varying approximately as ln(t) for a significant period of time, and (b) slow nucleation followed by rapid domain growth.These two limiting behaviors are illustrated in Fig. 1 for Dy/Fe compositionally modulated multilayer samples, where the polar Kerr angle 0&, which is proportional to the magnetization M, is plotted as a function of time. " These measurements were carried out by first saturating the sample with a large magnetic field perpendicular to the film and then reversing the field to a value near the coercive field H, (the applied field for which M=0) and holding it constant while the Kerr rotation was monitored. The dashed line shows the time dependence of the polar Kerr rotation of a Dy(5 A)/Fe(8. 1 A) sample, which illustrates type-(a) behavior. The Kerr rotation completely reverses only for applied fields greater than the saturation field (the applied field for which Otf irst reaches its maximum value), and at longer times the 0.2 0.1 0.0 -0.1 -0.2 2PP 400 600 Time (s} 800 FIG. 1. Measured Kerr rotation angle as a function of time after field reversal for Dy(5 A)/Fe(5. 6 A) (solid line) an...

Co 3 Sn 2 S 2 , a quasi-two-dimensional system with kagome lattice, has been found as a magnetic Weyl semimetal recently. In this work, the anisotropies of magnetization and transport properties of Co 3 Sn 2 S 2 were investigated. The high field measurements reveal a giant magnetocrystalline anisotropy with an out-of-plane saturation field of 0.9 kOe and an in-plane saturation field of 230 kOe at 2 K, showing a magnetocrystalline anisotropy coefficient K u up to 8.3 × 10 5 J m -3 , which indicates that it is extremely difficult to align the small moment of 0.29 μ B /Co on the kagome lattice from c axis to ab plane. The out-of-plane angular dependences of Hall conductivity further reveal strong anisotropies in Berry curvature and ferromagnetism, and the vector directions of both are always parallel with each other. For in-plane situation, the longitudinal and transverse measurements for both I // a and I  a cases show that the transport on the kagome lattice is isotropic. These results provide essential understanding on the magnetization and transport behaviors for the magnetic Weyl semimetal Co 3 Sn 2 S 2 .

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