Yu He

Uranus and Neptune have long puzzled scientists: their magnetic fields are heavily tilted and tangled, nothing like Earth's. The answer lay in an exotic form of water — superionic ice, which fills their interiors.

Just as Water changes phase, freezing into ice or evaporating into vapor, forsterite, a key mineral of Earth's mantle, under pressures of hundreds of thousands of atmospheres, reassembles its crystal lattice.

Picture an orchestra in which violins and trumpets play different parts but together create a powerful sound. In a crystal of the layered magnet Fe5GeTe2 doped with nickel, tiny regions of a different phase, Fe6GeTe2 nanoprecipitates, take on the role of those instruments. It is they, not the nickel itself, that keep the material magnetic at 478 kelvin, that is, at 205 degrees Celsius.