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Conceptual Graphene Node with Filtered Electron Spin Function: The blue nickel layer and the red iron layer contain electrons in two spin states (up and down). A few layers of graphene (graphene, a quasi-two-dimensional plane consisting of single-layer carbon atoms, Lei Fengnet) are placed between the two metal thin films to form a conductive path that allows electrons in only one direction to pass through. . After the current passes through this metal junction, it becomes a spin-polarized current.
In the history of spintronics, graphene has an unusual history. This kind of electronics uses the spin state of the electron itself to encode information, instead of using the electron's own charge to encode it. Initially, graphene did not appear in the field of vision. Because when the electrons spread through the plane of graphene, the spin state does not change, and the direction of electron movement is still random, and does not form a certain path.
However, a recent experimental result shows that graphene may have a great effect on spintronics, which also changes the opinion of scientific research project managers.
A team from the United States Naval Laboratory (NRL) recently conducted an experiment. They put a layer of graphene in the middle of several layers of nickel and iron. This layered structure, for the first time, realizes film-like nodes that can filter electron spins at room temperature.
This result may be of great help to the development of next-generation magnetoresistive random access memory (MRAM). The principle of MRAM is to use spin-polarized pulses to flip the magnetic information of the storage bits from 0 to 1 and vice versa.
Spin filtering this phenomenon makes it possible to acquire highly spin-polarized carriers. In fact, the principle of such a device is the same as that of a filter, which allows only one spin direction electron to pass through and hinders another spin direction electron. This allows the "up" and "down" spins of the electrons to be distinguished, thus forming "0" and "1" in the digital logic.
In this stacked structure, the spin-filtration phenomenon is caused by the interaction of the quantum mechanical properties of graphene and crystalline nickel films. After the nickel layer and the graphene layer are aligned, this structure allows only one electron in a particular spin direction to flow from the material to the other end.
“Spin filtration was theoretically predicted before, but it was previously confirmed only under low-temperature, high-resistance structures,†said Dr. Enrique Cobas, chief researcher at the NRL Materials Science and Technology Division, at a conference. "The new results confirm that this effect (spin filtering, Lei Fengwang note) can also exist in the low-resistance structure of various device matrices at room temperature."
In the journal ACS Nano's article, NRL researchers are exploring the electrical conductivity of graphene stacks and how they interact with other materials. To this end, NRL's team has created a new method that can directly fabricate large-scale multilayer graphene films on a flat sheet of nickel alloy film. This method maintains the magnetic properties of nickel alloy thin films so that they arrange these thin films into switch matrix nodes.
“We still have room for improvement, because theoretically, by finely adjusting the number of layers of graphene, this effect can be increased by an order of magnitude,†said Dr. Olaf van't Erve, a researcher at the NRL Materials Science and Technology Department at a press conference. . “However, the current model does not include the spin-rotation that occurs in ferromagnetic contact. When we take those effects into account, we can really approach the ideal state of 100% spin polarization. This can be achieved by We modify and optimize current equipment configurations and materials to maximize the effect."
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