Memory and Storage

Semiconductor Material Enables Spintronics Devices

20 February 2015

Researchers at the University of Michigan were successful in using a new compound acceptable to build spintronic properties into a material that's stable at room temperature and tailored to a variety of applications.

The new semiconductor compound could eventually be used as the base material for spintronic processors and other devices, much like silicon is the base for electronic computing devices.

Spintronics, unlike electronics, use both electrical charge and magnetic spin of electronics to store information, whereas electronics use only electrical charge. The advantage of spin-based circuits is they are smaller than charge-based circuits enabling more integrated devices in a single processor.

"You can only make an electronic circuit so small before the charge of an electron becomes erratic," said Ferdinand Poudeu, assistant professor of materials science and engineering at the University of Michigan.

Poudeu explained that the spin of electrons remains stable at much smaller sizes, which enables spintronics to be used in next-generation computing devices.

Another major advantage for spintronics devices is that data can be retained after power is shut off. This enables device designers to combine functions into a single device, as opposed to having different functions in separate components with current computing devices. For example, a single spintronic chip could handle three functions--a processor to make calculations, RAM memory for primary storage and a hard drive for secondary storage. This dramatically reduces the size and power consumption of computers.

The challenge has been to develop spintronic semiconductors with precise levels of both magnetism and conductivity that can maintain its properties over a range of temperatures. The obstacle has been the crystalline structure that makes up semiconductors.

Semiconductors are made of crystals with simple, symmetrical patterns, in microscopic lattices. The properties of those repetitive semiconductor lattices are controlled by adding atoms of different elements to the holes in a lattice. For example, adding bismuth increases conductivity, adding iron increases magnetism.

In spintronics fit atoms of different sizes need to fit with holes that are all similarly sized and regularly spaced. Podeu said researchers have been working to find new ways to add atoms to commonly used crystalline structures, to no avail.

Poudeu's team create an entirely new crystal structure, a mixture of iron, bismuth and selenium to create a complex crystal that offers much greater flexibility. Their low-symmetry crystal has holes of varying size placed at varying distances in multiple, overlapping layers.

The new crystal enables atoms to be arranged in multiple number of different combinations where conductivity and magnetism can be manipulated independently. The level of control opens spintronics to be manageable devices for an entire slew of applications, according to Poudeu.

The project used a cross-disciplinary team from chemistry, crystallography and computer science to build a new crystal.

His team tested the new compound in powder form and needs to make in thin film for use in a spintronic device.

The project research was supported by the National Science Foundation and the U.S. Department of Energy, Office of Basic Energy Sciences.

The online version of "Coexistence of High-T Ferromagnetism and n-Type Electrical Conductivity in FeBi2Se4" is in Journal of the American Chemical Society.

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