Magnetic semiconductor breakthrough may pave way for smaller, faster gadgets

Washington, Nov 26 : For the first time, researchers at the National Institute of Standards and Technology (NIST) have demonstrated the existence of a key magnetic, and not electronic, property, called antiferromagnetic coupling, of specially built semiconductor devices.

Antiferromagnetic coupling is a property of semiconductor devices in which one layer spontaneously aligns its magnetic pole in the opposite direction as the next magnetic layer.

The discovery of the new property may pave the way for even smaller and faster gadgets that could result from magnetic data storage in a semiconductor material, which could then quickly process the data through built-in logic circuits controlled by electric fields.

Currently, magnetic data storage is successfully utilized in consumer products such as computer hard drives and MP3 players- storage devices based on metallic materials. These conventional hard drives can only hold data; they have to send the data to a semiconductor-based device to process the data, which can slow down performance.

Now, researchers from NIST, Korea University and the University of Notre Dame have supported theories that thin magnetic layers of semiconductor material could exhibit antiferromagnetic coupling.

The discovery of antiferromagnetic coupling in metals was the basis of the 2007 Nobel Prize in Physics.

It was only recently that the property was considered useful in semiconductor materials. Semiconductors with magnetic properties would not only be able to process data, but also store it.

The most widely studied magnetic semiconductor is gallium arsenide (GaAs) with magnetic atoms (manganese) taking the place of some of the gallium atoms. It was predicted that by creating thin films of this material separated by a nonmagnetic material of just the right thickness and electrical properties, one could engineer antiferromagnetic (AF) coupling.

With magnetic fields, one could then switch the magnetization of one of the layers back and forth to create "spintronic" logic circuits, ones that operate not only under the usual control of electric fields but also the influence of magnetic fields (manipulating a property known as spin, which could be imagined as tiny internal bar magnets in particles such as electrons).

The researchers studied these multilayer stacks using a technique known as polarized neutron reflectometry, in which a beam of neutrons is bounced off the stacks.

Since neutrons are magnetic, and are able to easily penetrate through the entire stack, the reflected neutrons provide information about the magnetic properties of the individual layers.

At low temperatures and small magnetic fields, the polarized neutron data unambiguously confirm the existence of an antiparallel magnetic alignment of neighboring layers. When the magnetic field was increased, the neutron data indicated a parallel alignment of all layers.

The results showed that AF coupling is achievable in GaMnAs-based multilayers, a seminal property that now opens up a multitude of device possibilities for this novel material.

As the phenomenon only occurs at very cold temperatures in the material (about 30 K), the researchers believe these results will help inform theorists who could then better understand how to create room-temperature devices with the same magnetic properties.

ANI