According to classical electromagnetism, a charged
particle moving in an external magnetic field experiences a force
that makes the particle’s path circular. This basic law of physics
are exploited in designing cyclotrons that work as particle
accelerators. When nanometer-size metal particles are placed in a
magnetic field, the field induces a circulating electron current
inside the particle. The circulating current in turn creates an
internal magnetic field that opposes the external field. This
physical effect is called magnetic shielding.
