Attractive new magnetic material

A material that temporarily transforms itself into a "permanent" magnet when a small voltage is applied has been discovered by scientists in Japan.

Although substances with similar behaviours have been describedbefore, these have worked in this way only at super-low temperatures close to absolute zero. But what sets this new material apart is that it exhibits this magnetic phenomenon at room temperature.

Tokyo University's Tomoteru Fukumura and his colleagues, who have announced the discovery in this week's edition of the journal Science, made the new magnetic material by replacing 10% of the titanium atoms in titanium dioxide (TiO2) with cobalt atoms. The resulting titanium cobalt oxide compound, they found, is naturally "paramagnetic", meaning that it is weakly attracted by an applied external magnetic field. But, if a small voltage is applied, then the material becomes magnetic in its own right.

By making fine measurements of an entity called the anomalous Hall Effect, the team discovered that, when electrons are pushed into the substance by a voltage, the electrons of the cobalt atoms are triggered to all adopt the same direction of spin, which is what underpins the magnetic field created by a ferromagnetic material. This effectively turns the material into a "permanent" magnet, at least until the voltage is shut off.

被称为“变色龙磁铁”由于他们的能力to change their appearance in this way, the discovery is very exciting because it has the potential to open up a range of applications in an emerging field known as spintronics.

For instance, electrons can tunnel from a magnetic source material through a barrier to a second magnetic target much more easily if the two have the same magnetisation. And so a magnet that can be turned on and off could provide a miniature microswitch or transistor.

Magnetic materials also alter the polarisation of light reflecting off their surfaces. So if a magnet can be turned on and off very quickly and with high resolution, coupled with a polarising filter such a system could be used to control the brightness of a light source very rapidly in order to send a greater density of data down the fibre-optics that underpin modern communications networks, including the Internet.