To measure magnetisation relaxation rates at longer timescales, the technique of direct current (DC) magnetisation decay is often employed. In this approach, the sample is magnetised in a large external field, which is then quickly switched off, and the magnetisation versus time is measured. While any single molecule in a sample is expected to show a mono-exponential magnetisation decay, ensemble effects generally lead to the appearance of multi-exponential decays, which are commonly modelled via a stretched exponential function (SEF):