The Earth Related Robust Interpreted Language Laboratory (MERRILL) is a computer program written in the Fortran language that can simulate ferromagnetic materials using the micromagnetic theory. This computer software is developed at the University of Edinburgh.
Since micromagnetics is a continuum description of a magnetic system but computer calculations are numerically discrete, the system have to be discretized. In the case of MERRILL this is done by applying the Finite Element method, where the system’s geometry is partitioned into a mesh of tetrahedral units. This is generally more accurate for the simulation of complex geometries (relevant in rock magnetic samples), compared to the alternative Finite Difference method, where the system is partitioned into a mesh of cuboid units. The main disadvantages of the Finite Element method are the difficulty to program and to optimize the code, and in some cases the generation of good quality meshes. In the figure a ferromagnetic sphere is modeled using both Finite Elements and Finite Differences, where it can be seen that the surface is better approximated with the Finite Element method. The code MERRILL is oriented towards rock magnetism thus it includes several functions and variables to simulate ferromagnetic materials at different temperatures.