where Sj = ±1 represents which of the two states in Fig. ) is present at site j in the lattice; J⊥ is the coupling constant of nearest neighbors (denoted ⟨ij⟩). Since the coupling in the ab plane is ferrohexapolar (J⊥ > 0), neighbors favour the same spin state. We parameterise the value of J⊥ by fitting simulated data to experimental scattering using a small, representative area of intense DS (shown in purple in Figure ). The procedure for calculating DS from our model and fitting to data is detailed in the S.I.. In this way, correlations present in the 2048 atoms of our supercells can be encoded with a single parameter: J⊥ /Teff = 0.1361.