We present results of theoretical study of initial stage of spinodal decomposition and magneto-diffusion transport in ferrofluids with single-domain ferromagnetic nanoparticles. Effect of magnetic field and the long-ranged interparticle correlations on kinetics of this transformation is analyzed. © 2023, The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature.