Professor Thomas Schrefl from the Center for Integrated Sensor Systems at Danube University gave a talk to the NGCM group on Wednesday 2nd December on the use of simulation of magnetic systems in order to inform design of new magnets for industrial use.
He began by giving a brief summary of the current types of magnetic materials, which contain rare earth elements. Due to both environmental and commercial concerns, the continued use of these elements in the manufacturing of magnets is problematic, especially as demand increases for use in machinery and transport, such as in electric vehicle motors.
Thomas talked about his use of simulations in magnetics using finite elements. In simulating the roughly 200nm magnetic domains found in most magnetic materials he talked about a method of using a regularised Voronoi construction over a set of points which is then meshed, while taking care that the resulting grain size distribution of a simulated sample is close to that of a real magnet. He spoke about the need for regularisation in order to ensure that the finite elements are not too distorted from the parent elements.
He talked about the simulation of around 100 grains at a time, using an energy functional with anisotropy, exchange and magnetostatic contributions, alongside an applied external field.
Speaking about the computational aspects of his work, Thomas spoke about how through the use of GPU computations, a simulation of 16 million tetrahedral elements takes around 4 and a half hours. He mentioned the use of the Python Escript finite elements software, which supports OpenMP and MPI and allows users to describe their partial differential equations through simply specifying the coefficients of the partial derivatives rather than the normal practice of writing out the weak form as in other software such as FEniCS.
He then went on to talk about the different techniques for improving the properties of magnets with reduced heavy earth components, through the use of grain boundary engineering. Simulations have shown that magnets which are heated to allow diffusion of rare earth elements through the material require fewer atoms of rare earth elements in order to reach desirable magnetic properties.