Most familiar magnets are metals. They contain atoms that host tiny magnetic bar magnets, or moments, that can point up or down, and the atoms are surrounded by a sea of electrons. But researchers have long been interested in a different type of magnet, one consisting of widely separated magnetic ions embedded in a semiconductor. Unlike a metal, the number of free electrons in a semiconductor changes when it’s exposed to electric current or light, so these materials should provide new ways to influence the magnetic properties, via the electrons. Light can flip the magnetization–the total magnetic moment of atoms in a region–from up to down, for example. But until now, experimenters needed very bright light to weaken the magnetization enough to reorient it.
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replaced about one percent of the gallium atoms with the magnetic atom manganese. At temperatures below about 25 Kelvin
Sounds like a job for gadolinium (or a summer in San Francisco).