Flipping Atoms in a Flash

Researchers have found a very fast way to flip the magnetic alignment of atoms in a layer of nickel and iron, using an ultrashort pulse of laser light. The finding, reported in the 3 May issue of Physical Review Letters, could be used in future generations of hard disks, which use magnetic orientation to store information.

A material becomes magnetic when most of its atoms--which behave like tiny magnets--point in the same direction. One way to flip the direction of atoms in a small region of the material to record a bit of information is to expose it to a magnetic field, created by running electricity through a tiny wire loop. But electricity can be sluggish, so it takes some time to get the atoms to move. "We thought there might be some way of circumventing that process using short pulses of light," says Arto Nurmikko, a physicist at Brown University in Providence, Rhode Island.

The trick was to create a material in which the laser could briefly unpin the atoms, enabling an external field to rapidly reverse their direction. Nurmikko and his colleagues used a slice of a material made up of layers of nickel iron at the bottom and nickel oxide on top. Nickel iron is ferromagnetic; an external magnetic field can align its atoms. Nickel oxide is antiferromagnetic: atoms in adjoining layers point in opposite directions. But the interaction of the two materials at their interface creates an internal magnetic field that aligns all the atoms in the nickel iron layers. Because nickel oxide is transparent, the researchers could shoot a laser pulse lasting just a trillionth of a second through it to reach the top nickel iron layer. The pulse shook up the electrons in this layer, freeing the atoms from the internal field. Once this happened, the atoms in the nickel iron layer could flip direction in response to another magnetic field that the researchers had applied from the outside. Their magnetization reversed in just 10 billionths of a second, more than 10 times faster than in a conventional disk drive.

"This is an extremely clever experiment," says William Doyle, a physicist at the University of Alabama, Tuscaloosa. But whether the method will ever make it into computers is debatable, says Marcos Lederman, a storage technologist at Read Rite, a company in Fremont, California. The use of lasers and the complexity of the material may make the technology too expensive to be viable, he says.

Posted in Physics, Math