Researchers have created a material that acts as a magnetic diode, transferring magnetism from one object to another but not the other way around.
An electric current flowing through a coil of copper wire induces a magnetic field in the coil. This magnetic field can then transfer to a nearby magnetic object, such as a second coil of wire. The laws of electromagnetism, and experimental demonstrations to date, predict that this transfer is symmetric, meaning that magnetic fields move both from coil A to coil B and from coil B to coil A. Prat-Camps and his colleagues wondered if they could break this so-called magnetic reciprocity and make the magnetic-field transfer one way. The answer, they found, is yes, if both coils are placed in between the two walls of a hollow, rotating, conducting cylinder, where the walls have a U-shaped cross section.