No abstract

Topologically protected magnetic structures such as skyrmions and domain walls (DWs) have drawn a great deal of attention recently due to their thermal stability and potential for manipulation by spin current, which is the result of chiral magnetic configurations induced by the interfacial Dzyaloshinskii-Moriya Interaction (DMI). Designing devices that incorporate DMI necessitates a thorough understanding of how the interaction presents and can be measured. One approach is to measure growth asymmetry of chiral bubble domains in perpendicularly magnetized thin films, which has been described elsewhere by thermally activated DW motion. Here, we demonstrate that the anisotropic angular dependence of DW energy originating from the DMI is critical to understanding this behavior. Domains in Co/Ni multi-layers are observed to preferentially grow into non-elliptical teardrop shapes, which vary with the magnitude of an applied in-plane field. We model the domain profile using energetic calculations of equilibrium shape via the Wulff construction, which explains both the teardrop shape and the reversal of growth symmetry at large fields.

Marine renewable energy has the potential to solve both the energy-security and coastal-protection problems affecting coastal societies. In this article, the potential benefits arising from the combination of marine renewable energy technologies with infrastructural needs for coastal protection and other local needs are analysed. Classifications of technologies are developed to inform future coastal planning. Explanations of the resources and technologies are presented in layperson's term. The threat of coastal inundation under climate-change scenarios is a major global issue. The investment in new infrastructure demanded by cities, ports and communities at risk of inundation could very substantially reduce the levelised cost of electricity from renewable sources, provided the infrastructure is designed with the dual purpose of power generation and coastal protection. Correspondingly, the sale of electricity from such infrastructure could defray the long-term cost of installing coastal protection. Furthermore, many marine renewable energy technologies provide a platform on which other forms of renewable energy generation could be mounted. It is noted that the complex geophysical and engineering issues arising from this opportunity must be assessed considering socioeconomic factors.

Spin-transfer-torque magnetic random access memory (STT-MRAM) is the most promising emerging non-volatile embedded memory. For most applications, a wide range of operating temperatures is required, for example −40 °C to +150 °C for automotive applications. This presents a challenge for STT-MRAM, because the magnetic anisotropy responsible for data retention decreases rapidly with temperature. In order to compensate for the loss of thermal stability at high temperature, the anisotropy of the devices must be increased. This in turn leads to larger write currents at lower temperatures, thus reducing the efficiency of the memory. Despite the importance of high-temperature performance of STT-MRAM for energy efficient design, thorough physical understanding of the key parameters driving its behavior is still lacking. Here we report on CoFeB free layers diluted with state-of-the-art non-magnetic metallic impurities. By varying the impurity material and concentration to modulate the magnetization, we demonstrate that the magnetization is the primary factor driving the temperature dependence of the anisotropy and thermal stability. We use this understanding to develop a simple model allowing for the prediction of thermal stability of STT-MRAM devices from blanket film properties, and find good agreement with direct measurements of patterned devices.

No abstract