Fundamental theory of spintronics

[Keio Spintronics Network - Miyake Laboratory , Osaka University]

Professor Kohno at Osaka University is doing theoretical research on spintronics, from the viewpoint of fundamental physics.

Spintronics uses both the charge and spin of electrons in solids, to achieve electronic devices with new capabilities. Research on spintronics is currently very vigorous worldwide.

Q. "Usually, the aim of spintronics research is to apply it in industry. But I'm studying spintronics theoretically, from the viewpoint of fundamental physics. Specifically, I'm studying phenomena that properties of magnets are manipulated by electric currents, and conversely, dynamical information about magnetization is converted to electrical signals and detected."

The impetus for this research came from an experiment on current-driven domain wall motion.

In that experiment, a magnetic domain wall was moved by a current passing through a wire made of ferromagnetic material. Professor Kohno attempted to explain this experiment theoretically.

Q. "We derived an equation of motion of a domain wall under an applied current. The equation revealed that there are two mechanisms that drives domain walls."

These two mechanisms are spin transfer and momentum transfer. Professor Kohno devised a theory of these mechanisms from the microscopic viewpoint. He also generalized this theory to situations other than domain walls. The equations Professor Kohno obtained led to the idea of driving magnetic vortices by currents, which he suggested to experimenters.

Q. "By attaching leads to a magnetic disk which contains a vortex and passing a current through them, experimenters have succeeded in exciting the vortex core motion, and detecting this motion electrically."

In addition, it's been discovered that, if the current is increased, the orientation of the core can be reversed electrically.

Q. "Next, I calculated theoretically the effects that currents have on general magnetic structures, including domain walls, vortices and all others. The magnetization follows an equation of motion of this form. When there's interaction with the conduction electrons, another term is added to the equation. This is the magnetization, and this is the spin of conduction electrons, and their cross product affects the motion of magnetization. In other words, it acts as a torque. We can derive the effective torques by eliminating conduction electrons. In particular, these alpha and beta terms come from a rather delicate process called spin relaxation, which has to be handled rather precisely. We are constructing a theoretical framework that can treat such effects."

Q. "We're also investigating the inverse effect of spin torque, that is, the effect that magnetization dynamics has on electrons. Suppose a domain wall is driven by, e.g., magnetic field and is in motion. It's been proposed that then an electromotive force is generated. We are also studying this effect theoretically, by including spin relaxation effects, and gauge invariance. This phenomenon itself can be regarded as a mean to convert the information about magnetization dynamics into electrical signals. However, this effect is very small, and detecting it is an experimental challenge. Success has been achieved only recently; In 2008, a group in Texas detected the effect using magnetic domain walls."

Category:

Science & Technology

Tags:

• spintronics
• Hiroshi
• Kohno
• Osaka
• University

[Darkwizzrobe]

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[RunLiberty]

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[brianmenendez]

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[karlcheah]

thanks for this video @keiouniversity

[maintoc]

Thank you.