Novel magnetic nanocomposites (see Figure) are obtained by the self‐assembly in water of
polypeptide‐based diblock copolymers of polybutadiene‐block‐poly (glutamic acid)
combined with hydrophobically modified γ‐Fe 2 O 3 nanoparticles. These hybrid
supramolecular objects are either filled micelles (three dimensional) or hollow vesicles with
a magnetic membrane (two dimensional), the deformation of which, under an applied
magnetic field, has been evidenced.