Tohoku University

Tohoku University Research News of Engineering (Tune) is a biannual publication of School of Engineering (SoE), Tohoku University, Sendai, Japan. Each Tune volume provides the scientific community with the latest research results of SoE on a selected topic.


Probing the Dynamics of Spins Inside the Wall
Samik DUTTAGUPTA (Research Institute of Electrical Communication (RIEC), Tohoku University)

Probing the Dynamics of Spins Inside the Wall

The development of the modern semiconductor technology relies on the utilization and transport of the charge property of electron. However, it completely ignores another fundamental property: the electron spin. To go beyond the Moore’s law, the exploration of the spin property of the electron becomes important for technological advances in the nanoscale regime. Starting from 2013, I am working under the supervision of Prof. Hideo Ohno at the Laboratory of Nanoelectronics and Spintronics in Research Institute of Electrical Communication (RIEC). We work with ultrathin magnets and its dynamics. The main challenges were to understand the basic interaction in these systems and then to utilize them in demonstrating practical applications through novel devices. Thus, my research is directed towards the exploration of basic interactions in ultrathin magnetic systems.

The concept of spintronics emerged in the middle of 20th century after the establishment of quantum mechanics. The interesting results in metal-semiconductor-metal trilayer junctions led to the discovery of Giant Magnetoresistance in alternately arranged magnetic non-magnetic metallic multilayers. This paved the way of modern magnetic read heads in Hard Disk Drives. Subsequently, it was realized that the performance of GMR devices could be improved further with the discovery of Tunnel Magnetoresistance (TMR) where the non-magnetic metallic layer was replaced by a thin layer of insulator, which is the current center of attraction. The research on spintronics then progressed forward and today, encompasses a wide variety of topics bringing together different areas of sciences allowing successful exchange and sharing of several discoveries.

We know that magnets have two poles, the north and the south, representing the direction of the orientation of their moments. The transition region between the north and south poles, which is called a magnetic domain wall (DW). Magnetic DWs are prospective for the next- generation spintronic memory devices in terms of high speed, low energy consumption and reduction of the bit size. To achieve a successful implementation of DW memory devices, it is necessary to understand the interactions of the magnetic DW under the application of external magnetic field or spin-polarized electric current which is the focus of my research. The response of these magnetic DW on the application of these different forces enables the understanding of the basic physical laws governing the dynamics, these serving as important parameters for development of DW motion memory devices.

Our research encompasses several steps and systematic experiments. We start from the investigation of ultrathin magnetic thin films and subsequently fabricate devices for the understanding of DW motion in magnetic metallic systems. As the adage says, “seeing is believing,” sowe started with the investigation of the DW motion driven by magnetic field and current using optical measurement techniques. This versatile technique enables us to probe the dynamics of our system while visualizing down to the micrometer range. With our experiments at different temperatures (T) starting from room temperature in both low and high T regime, we are investigating the mechanism of DW motion in ultrathin metals when driven by magnetic field and current.

From a practical point of view, spintronics has an immense potential with direct impact on different sectors of society. The exploration of physics at the nanoscale, coupled with device technology and their successful implementation in practical applications, is taking us on a wonderful journey.