R&D: Fast Control Scheme of Ferromagnet for Energy-Efficient Storage

From Tohoku University, Japan

The digital data generated around the world every year is now counted in zettabytes, or trillions of billions of bytes – equivalent to delivering data for hundreds of millions of books every second.

The amount of data generated continues to grow. If existing technologies remained constant, all the current global electricity consumption would be devoted to data storage by 2040.

Researchers at the Université de Lorraine, France and Tohoku University, Japan, reported on an innovative technology that leads to a drastic reduction in energy for data storage.

The established technology utilizes an ultrafast laser pulse whose duration is as short as 30 femto seconds – equal to 0.0000000000000003 seconds. The laser pulse is applied to a heterostructure consisting of ferrimagnetic GdFeCo, nonmagnetic Cu and ferromagnetic Co/Pt layers.

“Previous research, conducted by a subset of the current research group, observed magnetic switching of the ferromagnetic layer after the ferrimagnetic layer had been switched.” This time, the researchers uncovered the mechanism accounting for this peculiar phenomena and found that a flow of electron spin, referred to as a spin current, accompanying the switching of ferrimagnetic GeFeCo plays a crucial role in inducing the switching of ferromagnetic Co/Pt (Fig. 1).

(Fig. 1) A schematic illustration of the demonstrated ultrafast and energy efficient switching of ferromagnet driven by a single femtosecond laser pulse. The laser pulse demagnetizes the ferrimagnetic layer and generates a spin current, which travels through the nonmagnet and finally induces the switching of the ferromagnet. The lower image shows an observed magneto-optical Kerr effect micrograph showing the switching of the ferromagnetic layer.
(Ⓒ Shunsuke Fukami and Stéphane Mangin)

Based on this insight, they demonstrated a much faster and less energy consuming switching of the ferromagnet. This was driven by a single laser pulse without a switching of the ferrimagnetic layer. “This is very good news for future data-storage applications as this technology can provide an efficient scheme to write digital information to a magnetic medium, which is currently based on a magnetic-field-induced switching,” says Shunsuke Fukami, co-author of the study.

The partnership between the Université de Lorraine and Tohoku University is driven, in large part, by the exchanges of graduate students and post-docs between the two universities. More than a dozen exchanges on both sides have already taken place for periods of several months. This partnership was supported by Presidents Hideo Ohno and Pierre Mutzenhardt, who signed a consortium agreement in 2019 during the World Materials Forum.

Article: Energy Efficient Control of Ultrafast Spin Current to Induce Single Femtosecond Pulse Switching of a Ferromagnet

Advanced Science has published an article written by Quentin Remy, Université de Lorraine, Institut Jean Lamour, UMR CNRS, Nancy, 7198 France, Junta Igarashi, Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, Satoshi Iihama, Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 6‐3 Aramaki Aza Aoba, Sendai, 980‐8578 Japan, and Center for Spintronics Research Network, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan,Grégory Malinowski, Michel Hehn, Jon Gorchon, Julius Hohlfeld, Université de Lorraine, Institut Jean Lamour, UMR CNRS, Nancy, 7198 France, Shunsuke Fukami, Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, WPI Advanced Institute for Materials Research, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, Center for Science and Innovation in Spintronics, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, Center for Spintronics Research Network, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, and Center for Innovative Integrated Electronic Systems, Tohoku University, 468‐1 Aramaki Aza Aoba, Sendai, 980‐0845 Japan, Hideo Ohno, Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, WPI Advanced Institute for Materials Research, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, Center for Science and Innovation in Spintronics, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, Center for Spintronics Research Network, Tohoku University, 2‐1‐1 Katahira, Aoba, Sendai, 980‐8577 Japan, and Center for Innovative Integrated Electronic Systems, Tohoku University, 468‐1 Aramaki Aza Aoba, Sendai, 980‐0845 Japan, and Stéphane Mangin, Université de Lorraine, Institut Jean Lamour, UMR CNRS, Nancy, 7198 France.

Abstract: “New methods to induce magnetization switching in a thin ferromagnetic material using femtosecond laser pulses without the assistance of an applied external magnetic field have recently attracted a lot of interest. It has been shown that by optically triggering the reversal of the magnetization in a GdFeCo layer, the magnetization of a nearby ferromagnetic thin film can also be reversed via spin currents originating in the GdFeCo layer. Here, using a similar structure, it is shown that the magnetization reversal of the GdFeCo is not required in order to reverse the magnetization of the ferromagnetic thin film. This switching is attributed to the ultrafast spin current and can be generated by the GdFeCo demagnetization. A larger energy efficiency of the ferromagnetic layer single pulse switching is obtained for a GdFeCo with a larger Gd concentration. Those ultrafast and energy efficient switchings observed in such spintronic devices open a new path toward ultrafast and energy efficient magnetic memories.“