Superparamagnetic nanoparticles have a randomly changing magnetic
moment57, and their assembly occurs when torque exerted by
a magnetic field exceeds nanoparticle thermal excitation energy54,57.
When magnetic nano particles placed in the magnetic field are sufficiently
close, they form 1D assemblies (chains) (Fig. 4a) or 3D
superlattices58. In chains, nano particles experience dipole–dipole
interactions with neighbouring nanoparticles, and to minimize the