Nd-Fe-B hard magnetic materials have been investigated intensively in recent years because of their high coercivities and maximum energy products. In this study we have examined the properties of the quaternary alloy Nd-Dy-Fe-B. Experiments revealed the underlying magnetic properties of these samples and these have been related to a theoretical model of the magnetization process. Samples were prepared in the form of particles either in the free state, in a randomly oriented state or in a field-oriented state obtained from solidification under an external field. Modeling results and microstructure analysis showed that compacting process strongly influenced the final magnetic properties through the change in the coupling coefficient resulting from one- or two-dimensional couplings among the particles which were totally different from those of the same materials in bulk state.