In today’s electronics, logic operations take place in semiconductors while information is stored in magnetic media. If it were possible to combine both functions on the same chip, or even in the same “bit”, revolutionary new types of devices might be built. The ability to control and manipulate the dynamics of both charge carriers and spin by external electric and magnetic fields (as well as light) is expected to lead to novel applications. This dream has spawned the exciting area of research known as “spintronics”, which awaits the discovery of semiconductors which are also ferromagnetic.

Numerous candidate materials have been found, but so far the most promising are magnetic only at very low temperatures, restricting their use to those applications where extreme refrigeration is economical. A few samples have exhibited magnetism at room temperature, only to be found inhomogeneous, containing tiny inclusions of magnetic phases embedded in a nonmagnetic semiconductor.

But in the summer of 2005 a new candidate was found, the III-V semiconductor InSb (indium antimonide) doped with small amounts of Mn (manganese), which is ferromagnetic at room temperature: even with less than 1% Mn content, the samples can be picked up with a magnet like paper clips with a refrigerator magnet!
Given previous disappointments, caution was in order: perhaps the manganese had “clumped” to form small magnetic inclusions. Using X-ray diffraction, the samples (produced in Russia) were shown to be highly homogeneous. But the magnetism might still be confined to the surfaces, as in some other examples; this would not be detected by the magnetic susceptibility measurements that confirmed a strong ferromagnetism at room temperature.

So the samples were brought to TRIUMF to be studied with the most sensitive known probe of local magnetism: the positive muon. Using µSR, an international team confirmed that the materials are magnetic throughout their volume at temperatures well above room temperature, an exciting conclusion that may pave the way for commercial development of spintronics devices.

Caution is still advised, of course: although InSb is an excellent semiconductor in its pure state (boasting the smallest effective electron mass of any of the III-V semiconductors), the effect of doping up to 1% Mn on its electronic properties is not yet fully explored, and the crucial interactions between electrons, holes and magnetism are still a matter of theoretical speculation.
But there is reason for guarded excitement.•