Spintronic devices promise to solve major problems in today's computers, which use massive amounts of electricity to generate heat. This requires expending even more energy for cooling. By contrast, spintronic devices generate little heat and use relatively minuscule amounts of electricity. Spintronic computers would require no energy to maintain data in memory. They would also start instantly and have the potential to be far more powerful than today's computers.
While electronics depend on the charge of electrons to generate the binary 1s or 0s of computer data, spintronics depends on the property of electrons called spin. Spintronic materials register binary data via the “up” or “down” spin orientation of electrons — like the north and south of bar magnets — in the materials. A major barrier to development of spintronic devices is generating and detecting the infinitesimal electric spin signals in spintronic materials.
Advances in spintronic devices could lead to new technology for computing and data storage. One advance is a method to detect signals from spintronic components made of low-cost metals and silicon, which overcomes a major barrier to wide application of spintronics. Previously, such devices depended on complex structures that used rare and expensive metals such as platinum.
A new technique detects the spin currents in a simple two-layer sandwich of silicon and a nickel-iron alloy called Permalloy. All three components are both inexpensive and abundant, and could provide the basis for commercial spintronic devices. They also operate at room temperature.
One side of the Permalloy-silicon bi-layer sandwich was heated to create a temperature gradient that generated an electrical voltage in the bi-layer. The voltage was due to a phenomenon known as the spin-Seebeck effect. The resulting “spin current” in the bi-layer could be detected due to another phenomenon known as the inverse spin-Hall effect. More efficient magnetic switching in computer memories could lead to development of such devices.
A key property for spintronics materials — called antiferromagnetism — could be generated in silicon, opening an important pathway to commercial spintronics, given that silicon is inexpensive and can be manufactured using a mature technology with a long history of application in electronics.
Ferromagnetism is the property of magnetic materials in which the magnetic poles of the atoms are aligned in the same direction. In contrast, anti-ferromagnetism is a property in which the neighboring atoms are magnetically oriented in opposite directions. These “magnetic moments” are due to the spin of electrons in the atoms, and are central to the application of the materials in spintronics.
Antiferromagnetism was detected in the two types of silicon — n-type and p-type — used in transistors and other electronic components. N-type semiconductor silicon is doped with substances that cause it to have an abundance of negatively charged electrons; p-type silicon is doped to have a large concentration of positively charged holes. Combining the two types enables switching of current in such devices as transistors used in computer memories and other electronics.
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