The Investigation into Magnetic Skyrmion Dynamics Under the Influence of the Interfacial Spin-Transfer Torque

Traditionally manufacturing processes have used a wide variety of sensors to provide process control, quality and productivity metrics. Industry 4.0 introduces the concept of combining and analysing sensor derived production data to offer greater insights into all aspects of manufacturing operations. A key area of advancement is the ability to process and analyse large volumes of data, in real-time, to provide to process control. The objective of this thesis is to define a framework that enables adaptive, optimised production control via the use of automated machine learning algorithm selection. The complete framework is capable of adaptively processing streamed production data directly from manufacturing processes along with other appropriate sources. To achieve this, a second longer term channel is used to autonomously evaluate and optimise competing algorithms and data strategies to select the most appropriate solution for near real-time control. A series of experiments demonstrates that the framework is suitable for production control applications which benefit from a focus on single or multiple accuracy metrics. The framework can automatically switch algorithms via a supervisory mode. This allows it to take into account additional factors such as concept drift, production changes, computational complexity and algorithm stability. Algorithm switching is based on a flexible optimisation strategy for algorithm performance over variable time periods. Experimental results are provided for two optimisation methodologies. Further development of the framework will involve full automation of the real-time algorithm selection method. This will remove the need for specialist data processing knowledge and hence allow the framework to be deployed in a wide range of existing manufacturing companies

Role of an additional interfacial spin-transfer torque for current-driven skyrmion dynamics in chiral magnetic layers

Skyrmions can be driven by spin-orbit torques as a result of the spin Hall effect. Here we model an additional contribution in ultra-thin multilayers, arising from the spin accumulation at heavy metal / ferromagnetic interfaces and observe the effects on a large range of skyrmion diameters. The combination of the interfacial spin-transfer torque and the spin-orbit torque results in skyrmion motion which helps to explain the observation of small skyrmion Hall angles for skyrmion diameters less than 100 nm. We show that this additional term has a significant effect on the skyrmion dynamics and leads to rapidly decreasing skyrmion Hall angles for small skyrmion diameters, as well as a skyrmion Hall angle versus skyrmion velocity dependence nearly independent of the surface roughness characteristics. Also, the effect of various disordered energy landscapes, in the form of surface roughness, on the skyrmion Hall angle and velocity is shown to be largely drive-dependent. Our results show good agreement with those found in experiments thus concluding that the interfacial spin-transfer torque should be included in micromagnetics simulations for the reproduction of experimental results

Computation of magnetization, exchange stiffness, anisotropy, and susceptibilities in large-scale systems using GPU-accelerated atomistic parallel Monte Carlo algorithms

Monte Carlo algorithms are frequently used in atomistic simulations, including for computation of magnetic parameter temperature dependences in multiscale simulations. Even though parallelization strategies for Monte Carlo simulations of lattice spin models are known, its application to computation of magnetic parameter temperature dependences is lacking in the literature. Here we show how, not only the unconstrained algorithm, but also the constrained atomistic Monte Carlo algorithm, can be parallelized for any spin–lattice crystal structure. Compared to the serial algorithms, the parallel Monte Carlo algorithms are typically over 200 times faster, allowing computations in systems with over 10 million atomistic spins on a single graphical processing unit with relative ease. Implementation and testing of the algorithms was carried out in large-scale systems, where finite-size effects are reduced, by accurately computing temperature dependences of magnetization, uniaxial and cubic anisotropies, exchange stiffness, and susceptibilities. In particular for the exchange stiffness the Bloch domain wall method was used with a large cross-sectional area, which allows accurate computation of the domain wall width up to the Curie temperature. The exchange stiffness for a simple cubic lattice closely follows an mk scaling at low temperatures, with k < 2 dependent on the anisotropy strength. However, close to the Curie temperature the scaling exponent tends to k = 2. Furthermore, the implemented algorithms are applied to the computation of magnetization temperature dependence in granular thin films with over 15 million spins, as a function of average grain size and film thickness. We show the average Curie temperature in such systems may be obtained from a weighted Bloch series fit, which is useful for analysis of experimental results in granular thin films

A philosophy to fit “the character of this historical period”? Responses to Jean-Paul Sartre in some British and American philosophy departments, c. 1945 - 1970.

Anglophone philosophers are often associated with rejecting philosophy’s moral guidance function after 1945. This article builds on existing work on Jean-Paul Sartre’s reception in universities to show that, actually, many British and American philosophers embraced moral guidance roles by engaging with his work and that they promoted creativity and choice in society as a result. Sartre first came to philosophers’ attention in the context of post-war Francophilia, but interest in him quickly went beyond the fact that he was French and expanded to include the wider existentialist movement that he was a part of. Sartre had enduring popularity among English speaking philosophers because his philosophy resonated with the older British and American philosophies idealism and pragmatism that, like his, were inspired by Hegel. Sartre’s respondents also valued existentialism because, to them, it made certain Judeo-Christian principles relevant, thus protecting religion at a time when they believed it was threatened with decline, and by the advance of specialisation. Anglophone philosophers who were interested in Sartre spread their responses to him through teaching an expanding student population, but also reached the wider public through activism, journalism, broadcasting, and government advisory roles. In doing so, philosophers integrated existential ideas into several aspects of culture in post-war Britain and America