Spintronics: scientists find new magic in magnetic material
09 May 2013
Scientists have confirmed the presence of a magnetic field generated by electrons which hitherto had only been thought to exist in theory.
The discoveryg expands the potential for harnessing the 'spin' or magnetic properties of electrons, adding a fundamental new building block to the pioneering field of spintronics.
Today’s semiconductors, which are essential to the operation of a broad array of electronics, carry along the electrical charge of electrons, but make no use of their magnetic or spin properties. Professor John Xiao and his team at the University of Delaware (UD) are working to unveil those properties at UD’s Centre for Spintronics and Biodetection.
In the presence of a magnet, an electron will take a 'spin up' or 'spin down' position, correlating to the binary states of 1 or 0 that computers use to encode and process data. One spin state aligns with the magnetic field, and one opposes it. A spintronics device requires an excess number of either spin-up or spin-down electrons. Controlling the direction of the magnetisation is a major goal in this field.
For the past few years, scientists have succeeded in generating a pure spin current in which electrons with opposite spins move in opposite directions. This is achieved by passing an electrical current through a heavy metal that’s not magnetic, such as platinum, tungsten or tantalum.
However, in a double layer of heavy metal and ferromagnetic material (for example, iron or cobalt), this pure spin current will diffuse into the ferromagnetic material. When this occurs, Xiao and his team have detected a magnetic field, which can switch the material’s magnetisation.
This magnetic field is confined inside the ferromagnetic material unlike the conventional magnetic field generated from a magnet, which is difficult to shield. Xiao says this finding is particularly important to high-density integrated circuits, such as magnetic random access memory, in which shielding the magnetic field between cells is, in his words, “a nightmare.”
“This magnetic field was predicted previously but was never experimentally confirmed. We demonstrated that it’s there,” says Professor Xiao. “We now have a new means of generating a magnetic field and controlling the direction of a nanomagnet, as well as a new measurement technique to characterise the magnetic field.”