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John O | January 2019

MIT advancing research into spintronic memory devices with new process to make skyrmions


By Josh Perry, Editor
jperry@coolingzone.com

 

Researchers from the Massachusetts Institute of Technology (MIT) in Cambridge, Mass. have published three separate papers demonstrating the ability to produce record-setting, stable, and fast-moving skyrmions, magnetic quasi-particles with the potential for use in spintronics memory devices, at room temperature.

 


Could spintronics be the future of memory storage devices? MIT researchers advanced that study with three papers. (Wikimedia Commons)

 

Skyrmions, according to the report from MIT, are circular clusters of electrons that have a spin orientation the opposite of the surrounding electrons. The spin is either clockwise or counter-clockwise.

 

In one experiment, the scientists created a wire from a stack of 15 layers of a metal alloy composed of platinum, a magnetic material of cobalt-iron-boron, and magnesium-oxygen. The interface between the platinum and the magnetic layer is where skyrmions can form after an external magnetic field is applied.

 

“Notably, under a 20 milliTesla field, a measure of the magnetic field strength, the wire forms skyrmions at room temperature,” the report explained. “At temperatures above 349 kelvins (168 degrees Fahrenheit), the skyrmions form without an external magnetic field, an effect caused by the material heating up, and the skyrmions remain stable even after the material is cooled back to room temperature.”

 

The researchers were able to create a theoretical framework for determining the internal skyrmion size and structure and what composition of layers will produce what size skyrmion.

 

A second study used a different magnetic layer, gadolinium cobalt alloy, and tantalum oxide. Using these materials, researchers created skyrmions as small as 10 nanometers, which is a world record at room temperature. They also moved the skyrmions, using current driven domain wall motion, at a speed of 1.3 kilometers per second, also a world record.

 

“In a ferromagnet, such as cobalt-iron-boron, neighboring spins are aligned parallel to one another and develop a strong directional magnetic moment,” the article noted. “To overcome the fundamental limits of ferromagnets, the researchers turned to gadolinium-cobalt, which is a ferrimagnet, in which neighboring spins alternate up and down so they can cancel each other out and result in an overall zero magnetic moment.”

 

Using X-ray holography with partners in Germany, images of skyrmions were taken.

 

According to the report, “Solid-state devices built on these skyrmions could someday replace current magnetic storage hard drives. Streams of magnetic skyrmions can act as bits for computer applications.”

 

The research was recently published in Advanced Materials, Nature Nanotechnology, and Physical Review B. The abstract from the Advanced Materials paper read:

 

“Magnetic skyrmions promise breakthroughs in future memory and computing devices due to their inherent stability and small size. Their creation and current driven motion have been recently observed at room temperature, but the key mechanisms of their formation are not yet well?understood.

 

“Here it is shown that in heavy metal/ferromagnet heterostructures, pulsed currents can drive morphological transitions between labyrinth?like, stripe?like, and skyrmionic states. Using high?resolution X?ray microscopy, the spin texture evolution with temperature and magnetic field is imaged and it is demonstrated that with transient Joule heating, topological charges can be injected into the system, driving it across the stripe?skyrmion boundary.

 

“The observations are explained through atomistic spin dynamic and micromagnetic simulations that reveal a crossover to a global skyrmionic ground state above a threshold magnetic field, which is found to decrease with increasing temperature.

 

“It is demonstrated how by tuning the phase stability, one can reliably generate skyrmions by short current pulses and stabilize them at zero field, providing new means to create and manipulate spin textures in engineered chiral ferromagnets.”

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