Interactions in Nanoscale Arrays of Soft Magnetic Bi-Layers
Magnetic bi-layers are becoming increasingly popular as a medium for perpendicular patterned media. In order to understand the net interactions between the layers and between adjacent magnetic elements in an array, we use a coupled Preisach model to model the hysteresis loops we measured for a sample consisting two magnetically soft layers of FeCoTaZr, separated by an 0.8-nm Ru spacer layer. The model reproduces the major hysteresis loop to decent agreement. The model was then decoupled to reveal the reversal behavior of the individual layers. This paper demonstrates that coupled Preisach modeling of the hysteresis loop is an effective tool to analyze such interacting material systems.
Micromagnetic structure of Co stripe arrays with tuned anisotropy
An interwire magnetostatic coupling is one of the most important effects in the micro- and nanowire arrays, because of it strongly influences on the magnetization switching, spin-wave dynamics and magneto-transport properties. Manipulation of the magnetostatic coupling is possible not only by variation of a dimension of nanowires and geometry of arrays, but also by changing the magnetic anisotropy. In this paper, we report on an investigation of the magnetic behavior of arrays consisting of finite number of Co microstripes with two mutually perpendicular induced anisotropies. We have studied an effect of the interwire coupling on the switching field of magnetization and analyzed the domain structure of the arrays under an impact of the induced anisotropies.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.