|The researchers were experimenting with ferromagnet/semiconductor (FM/SC) structures, which are key building blocks for semiconductor spintronic devices (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).
The researchers found that by simply altering the thickness of the MgO interface they were able to control which kinds of electrons, identified by spin, traveled from the semiconductor, through the interface, to the ferromagnet.
|The researchers found that when the structure's MgO interface is very thin (less than two atomic layers), spin down electrons pass through to the ferromagnet, while spin up electrons are reflected back, leaving only spin up electrons in the semiconductor.
They also found that when the interface is thicker than six atomic layers, both spin up and spin down electrons are reflected back, leaving electrons with zero net spin in the semiconductor.
But the surprising result for the researchers was that at an intermediate thickness, ranging from two to six atomic layers, the selectivity of the interface completely changes.
"We see a dramatic and complete reversal in the spin of electrons that pass through the interface," said Roland Kawakami, an assistant professor of physics who led the research team. "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."
According to his research team, such a "spin reversal" can be used to control current flow.