The authors describe how reverse Monte Carlo (RMC) modelling may be used to analyse neutron diffraction data from a disordered magnetic material. By applying the technique to the amorphous binary alloy Dy₇Ni₃ they determine both an atomic structure and a magnetic structure which reproduce the diffraction data. The atomic structure is found to be essentially random close packed while the magnetic structure at low temperatures is dominantly ferromagnetic. The development of short and long range magnetic order can be followed as the temperature is decreased below the Curie temperature. They anticipate that this technique, already employed for the determination of many different types of disordered atomic structures, will also be of great use in the determination of disordered magnetic structures in amorphous and crystalline magnetic materials.