Title of Presentation

“Spintronics －From Synthesis of III-V Magnetic Semiconductors to VLSI Applications－”

I have been engaged in the study of spintronics for nearly 30 years. Spintronics refers to “electronics utilizing the spin property of electrons.” Magnets, whose properties have been known since the times of the ancient Greeks and Chinese, are typical examples of material in which an orderly state of aligned spins exists. Used in electric motors and for non-volatile recording of data on hard disks, magnets are essential materials in today’s world.

While the properties of a magnet are inalterable once it is made, the resistance of a semiconductor, another essential material in today’s world, can subsequently be electrically altered. Finding potential ways to bridge the gap between these two types of materials was what I had in mind when embarking on my studies.

I first took a path in that direction whilst working in the laboratory of then IBM fellow Dr. Leo Esaki as a visiting scientist for 18 months, starting in 1988. Together with a group member at IBM, I set the objective of my research there to create a magnetic material using a group III-V compound semiconductor, a type that was increasingly being utilized in devices. Fortunately, we succeeded in synthesizing (In,Mn)As, a mixed crystal not found in nature, comprising a group III-V compound semiconductor, InAs, and a magnetic atom, Mn. We also discovered through applying a variety of growth conditions that it could be magnetized in low temperatures to become a ferromagnetic semiconductor.

I further pursued this theme at Tohoku University, where my initial activity was a research collaboration with Dr. Tomasz Dietl from Poland which demonstrated, by means of a theoretical model, carriers’ contributions to ferromagnetic phase stability. This opened up the possibility of electrical control of magnetic properties (or spin) because carrier concentrations can be electrically controlled. After overcoming some technical challenges, control of ferromagnetic properties using field effects at the interface between an insulator and a semiconductor was achieved. A series of experiments further demonstrated that the ferromagnetic phase transition temperature of a ferromagnetic material can be controlled through varying the number of carriers using electrical fields and that important properties of a magnet, such as coercivity and magnetic anisotropy, are modulated via spin-orbit interaction.

Starting with creation of a material, we ultimately demonstrated that properties of a magnet can be controlled even after it is made. Our results inspired a number of researchers to broaden the scope of research to metal magnetic materials. Now, energy-efficient non-volatile memory devices are being developed which utilize electric field-controlled magnetization switching.

The series of studies also led to the invention of a device with potential for various applications. This discovery came about during the process of applying electric field control to metallic materials. To enable electric field control, the ferromagnetic metal material needs to be a film as thin as several nanometers of thickness. With regard to a key combination for application — namely, CoFeB (magnet) and MgO (insulator) — with an ultra-thin CoFeB film, the perpendicular magnetic anisotropy at the interface between the insulator and the ferromagnetic metal successfully induced a perpendicular magnetization easy axis, which would be essential for realizing a high-performance device. Shortly thereafter, we fabricated a 40-nm scale microscopic spintronic device called a magnetic tunnel junction (MTJ) device, and we published the results after verifying that high performance had been achieved. That was in 2010. Today, the device structure has become a global standard and is widely used in spintronic devices for integrated circuits.

My presentation will also touch on some episodes for the purpose of sharing with the audience the excitement and dynamism of our research activities.

Profile

Web Site URL

http://www.ohno.riec.tohoku.ac.jp/
http://www.cems.riken.jp/en/?lang=en

A brief Biography

Hideo Ohno obtained his Ph.D. in Engineering from the School of Engineering at the University of Tokyo (1982). After serving successively as a lecturer (1982-1983) and an associate professor (1983-1994) in the Department of Electrical Engineering, Faculty of Engineering at Hokkaido University, he became a visiting scientist at the IBM Thomas J. Watson Research Center in the United States (1988-1990) before being appointed as a professor of the Department of Electronic Engineering, School of Engineering at Tohoku University (1994-1995), professor at the Research Institute of Electrical Communication, Tohoku University (1995-), and director of the Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University (2004-2010 and 2012-2013). At the University, he now serves concurrently as director of the Center for Spintronics Integrated Systems (2010-), principal investigator at the Advanced Institute for Materials Research (2010-), director of the Research Institute of Electrical Communication (2013-), professor at the Center for Innovative Integrated Electronic Systems (2012-) and director of the Center for Spintronics Research Network (2016-). Major research projects in which he has been involved include JSPS Research for the Future Program (Project Leader, 1994-2002); Strategic Basic Research Programs of the Japan Science and Technology Corporation (now the Japan Science and Technology Agency) (Research Director, 2002-2008); IT Program, RR2002, Ministry of Education, Culture, Sports, Science and Technology (Project Leader, 2002-2007); Research and Development Project for ICT Key Technology to Realize Future Societies by MEXT (Project Leader, 2007-2012); Research and Development for Next-generation Information Technology by MEXT (Project Leader, 2012-); Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program) by the Cabinet Office (Core Researcher, 2010-2014); Impulsing Paradigm Change through Disruptive Technologies Program by the Cabinet Office (Project Leader, 2014-). He is also a fellow of the Institute of Physics (UK), the Japan Society of Applied Physics, and the American Physical Society; a Distinguished Professor at Tohoku University; and a member of the Science Council of Japan (Secretary of Section III).

Details of selected Awards and Honors

1998	IBM Japan Science Prize
2003	IUPAP Magnetism Prize
2005	Japan Academy Prize
2005	Agilent Technologies Europhysics Prize
2011	Thomson Reuters Citation Laureate
2012	JSAP Outstanding Achievement Award
2012	IEEE David Sarnoff Award
2015	JSAP Compound Semiconductor Electronics Achievement Award
2016	Leo Esaki Prize
2016	C&C Prize

A list of selected Publications

H. Ohno, H. Munekata, T. Penney, S. von Molnár, and L.L. Chang, “Magnetotransport properties of p-type (In,Mn)As diluted magnetic III-V semiconductors,” Physical Review Letters, vol. 68(17), pp. 2664-2667, 1992

H. Ohno, A. Shen, F. Matsukura, A. Oiwa, A. Endo, S. Katsumoto, and Y. Iye, “(Ga,Mn)As: A new diluted magnetic semiconductor based on GaAs,” Applied Physics Letters, vol. 69 (3), pp. 363-365, 1996

H. Ohno, “Making nonmagnetic semiconductors ferromagnetic,” Science, vol. 281, pp. 951-956, 1998.

Y. Ohno, D. K. Young, B. Beschoten, F. Matsukura, H. Ohno, and D. D. Awschalom, “Electrical spin injection in a ferromagnetic semiconductor heterostructure,” Nature, vol. 402, pp. 790-792, 1999

T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, “Zener model description of ferromagnetism in zinc-blende magnetic semiconductors,” Science, vol. 287, pp. 1019-1022, 2000

H. Ohno, D. Chiba, F. Matsukura, T. Omiya, E. Abe, T. Dietl, Y. Ohno, and K. Ohtani, “Electric-field control of ferromagnetism,” Nature, vol. 408, pp. 944-946, 2000

S. Ikeda, K. Miura, H. Yamamoto, K. Mizunuma, H. D. Gan, M. Endo, S. Kanai, J. Hayakawa, F. Matsukura, and H. Ohno, “A perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction,” Nature Materials, vol. 9, pp. 721-724, 2010

S. Fukami, C. Zhang, S. DuttaGupta, A. Kurenkov, H. Ohno, “Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer system,” Nature Materials, vol. 15, pp. 535-541, 2016.

S. Kanai, F. Matsukura, and H. Ohno, “Electric-field-induced magnetization switching in CoFeB/MgO magnetic tunnel junctions with high junction resistance,” Applied Physics Letters, vol. 108, 192406 (4 pages), 2016.

S. Souma, L. Chen, R. O. dowski, T. Sato, F. Matsukura, T. Dietl, H. Ohno, and T. Takahashi, “Fermi level position, Coulomb gap, and Dresselhaus splitting in (Ga,Mn)As,” Scientific Reports, vol. 6, 27266 (10 pages), doi:10.1038/srep27266, 2016.