Tuning the interactions of a magnetic colloidal suspension.

We present a versatile experimental system of magnetic charged nanospheres dispersed in water that belongs to both dipolar and electrostatic systems. In this system, the interactions can be continuously tuned by varying the ionic strength I. At low I, the potential is a strongly repulsive Yukawa potential that leads to a phase diagram similar to the one of repulsive spheres (fluid and solid phases). At high I, the potential is a globally attractive Lennard-Jones potential that leads to a phase diagram similar to the one of atomic systems (gas, liquid, fluid, and solid phases).