As reported by Philip Ball in Nature, the material is an aerogel: a solid so porous that it is almost entirely air. It is made of small particles of silica, the fabric of sand and window glass, in a rigid yet tenuous network that is seasoned with tiny magnetic particles. Fine grains of a strongly magnetic mixture of neodymium, iron and boron, denoted Nd2Fe14B, are blended with the reagents that make the silica particles. The resulting magnetic aerogel is more or less transparent, albeit darkened.
Others have made magnetic aerogels before by similar means. These have tended to incorporate ‘soft’ magnetic particles – applying a magnetic field flips the alignment of their magnetic poles relatively easily. Soft magnets are unsuitable for some applications. For example, if they are used for recording magnetic information, nearby magnetic fields can wipe the memory rather easily, and information can also vanish if it is stored too densely.
Hard magnets like Nd2Fe14B, on the other hand, are difficult to flip, making them attractive for permanent memories. It takes a large magnetic field to flip the field orientation of the new aerogel. A magneto-optic display made from a transparent magnet like this could work rather like a conventional liquid-crystal display, containing pixel windows that switch between open and closed to the passage of polarized light. But they would be switched by magnetic rather than electric fields.
This research by developers Mart Gich and coworkers is reported in Applied Physics Letters.