Known techniques for modelling hysteresis characteristics of magnetic materials involve generating approximate data corresponding to an initial magnetisation curve of the magnetic materials. A disadvantage of this approach is that no account is taken of hysteresis effects. The present invention overcomes these disadvantages by generating a model of a magnetic material, comprising a first order non-linear differential equation for a first order non-linear dynamic system, the equation comprising a non-linear gain function and a non-linear lag function. A plurality of measurements of at least one parameter of the magnetic material are then made, and the first order gain and lag functions are empirically determined using the plurality of measurements. The apparatus thus generates a model of the magnetic material of improved accuracy and hence utility.