  The paper describes some characteristics of the "P" curves for structural
characterization of magnetic nano-particles suspensions (complex fluids,
complex powders, complex composite materials, or living biological materials
having magnetic properties). In the case of these materials, the magnetic
properties are conferred to various carrier liquids by artificially integrating
in their structure ferromagnetic particles of different sizes. The magnetic
properties are usually shown by the hysteresis curve. The structure can be seen
on (electronic) micrography. The P curves offer another possibility to
determine the structure of the magnetic component of a complex fluid by
numerical analysis of the magnetization curve experimentally obtained. The
paper presents a detailed approach of the P curves and some limitations in
their use.
