Counterclockwise 'Spin' Proven After 60 Years... A Step Forward for Spin Semiconductors

Schematic diagram of the left precession motion of the magnetic material (left) and schematic diagram of the right precession motion of the magnetic material.

[Asia Economy Reporter Junho Hwang] The Quantum Spin Team at the Quantum Technology Research Institute of the Korea Research Institute of Standards and Science (KRISS) unexpectedly detected a counterclockwise rotating spin one early morning while conducting spin research, which initially upset their mood. They thought the strange data resulted from mishandling equipment while dozing off during the experiment. After rechecking the equipment the next day and repeating the experiment, the team obtained the same data. Through further verification, the team realized that they had discovered the counterclockwise spin wave for the first time in 60 years since its theoretical introduction. The team also experimentally proved the counterclockwise spin wave for the first time in the world through additional research.

The KRISS Quantum Spin Team announced that they experimentally demonstrated the counterclockwise rotating spin wave, which had only been theoretically known since the 1960s, and that the related paper was published in Nature Materials on the 30th (local time).

Experimental Proof of Counterclockwise Rotating Spin Wave

The research team, in collaboration with Dr. Sugil Lee, Professor Gapjin Kim, and Professor Segwon Kim from the Korea Advanced Institute of Science and Technology (KAIST), measured spin waves exhibiting left-handed precessional motion (a type of motion where the rotation axis of a rotating body itself rotates) in the CoGd ferrimagnet, where the transition metal cobalt and rare earth gadolinium are mixed in a certain ratio, and revealed the related physical phenomena based on this.

When a magnet is divided down to the size of an electron, it exhibits precessional motion rotating clockwise. However, in the case of cobalt and gadolinium aligned antiparallel, the overall system can exhibit counterclockwise rotation due to the magnetization of gadolinium, which has a larger rotational inertia.

The public research team experimentally verified the theory using Brillouin light scattering, a technique that utilizes the collision between light and spin waves. They irradiated light onto the CoGd ferrimagnet to collide with the spin waves and analyzed the reflected light to determine the energy and momentum of the spin waves. The team observed left-handed motion for the first time in the tens of picoseconds (ps, one trillionth of a second) range and newly revealed phenomena such as the spin wave energy converging near zero at the magnetization compensation temperature of the ferrimagnet and the angular momentum compensation temperature increasing with the magnetic field.

Senior Researcher Chanyong Hwang of KRISS stated, "Until now, theories and experiments have been based only on magnetization rotating to the right. By identifying the left-handed motion of spin waves for the first time, we expect a new horizon to open in the development of next-generation spintronic devices."

The research team anticipates that additional research will enable the development of ultrafast, low-power semiconductor devices. By analyzing the spin rotation direction and further studying the physical causes and control methods related to spin precession, it will be possible to freely control the electron spin direction and use this to store information. This paves the way for the development of next-generation semiconductor devices.

In particular, spin waves operate at very high frequencies ranging from several gigahertz (GHz) to terahertz (THz), which means power consumption is very low, making it possible to develop ultrafast, low-power semiconductor devices.

Meanwhile, semiconductor-based electronic devices have achieved today's advancements by controlling only the charge of electrons with electric fields, one of the two properties of electrons: charge and spin. However, as these devices face physical limitations such as memory storage capacity and heat dissipation limits due to miniaturization, research utilizing spin is rapidly emerging.

This content was produced with the assistance of AI translation services.