New simple way to control electron 'spin' may help develop faster computers

Washington, June 24 : Researchers at UC Riverside say that they have devised a simple technique for controlling the "spin" of electrons and current flow, which may help change how information in computers can be transported or stored.

The researchers believe that the discovery they made accidentally while working in their lab might help in the development of spin-based semiconductor technology, such as ultrahigh-speed computers.

They have revealed that they made this discovery while experimenting with ferromagnet/semiconductor (FM/SC) structures, which are key building blocks for microelectronic devices that perform logic operations using the spin of electrons.

The FM/SC structure is sandwich-like in appearance, with the ferromagnet and semiconductor serving as microscopically thin slices between which lies a thinner still insulator made of a few atomic layers of magnesium oxide (MgO).

During the study, the researchers observed that just by simply altering the thickness of the MgO interface, it was possible to control which kinds of electrons, identified by spin, travelled from the semiconductor, through the interface, to the ferromagnet.

Writing about their findings in Physical Review Letters, the researchers have pointed out that the spin of an electron is represented by a vector, pointing up for an Earth-like west-to-east spin; and down for an east-to-west spin.

While experimenting with the FM/SC structures, the researchers found that both spin up and spin down electrons could travel from the semiconductor to the ferromagnet.

The researchers observed that when the structure's MgO interface was very thin (less than two atomic layers), spin down electrons passed through to the ferromagnet, while spin up electrons were reflected back, leaving only spin up electrons in the semiconductor.

They also observed that when the interface was thicker than six atomic layers, both spin up and spin down electrons were reflected back, leaving electrons with zero net spin in the semiconductor.

However, the researchers were surprised to see that at an intermediate thickness, ranging from two to six atomic layers, the selectivity of the interface completely changed.

"We see a dramatic and complete reversal in the spin of electrons that pass through the interface. This time, spin up electrons pass through while spin down electrons are reflected back to the semiconductor. In other words, the thickness of the MgO interface determines whether spin up or spin down electrons are allowed to pass through it," said Roland Kawakami, an assistant professor of physics who led the research team.

The researchers are of the opinion that such a "spin reversal" can be used to control current flow.

"Electron spins are oriented at random in an ordinary electric circuit, and, therefore, do not affect current flow. But if spin is polarized, that is, aligned in one direction, you can manipulate the flow of current and the transport of information - a feature that would be of great interest to the semiconductor industry. What is amazing is that only a couple of atomic layers of MgO can completely reverse the spin selection of the interface. This is unexpected because MgO is not a magnetic material," said Yan Li, the first author of the research paper, who made the discovery.

She revealed that the research team would next try to develop electronic devices based on the spin reversal.

"This will not only test its feasibility for applications, but also help determine the cause of the spin reversal, which is still unclear," she said.

ANI