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Clarification of Mechanism of Ferromagnetism in Diluted Magnetic Semiconductor

Release Date
25 Feb, 2014
  • BL07LSU (University-of-Tokyo Synchrotron Radiation Outstation)

The University of Tokyo
Japan Atomic Energy Agency (JAEA)
Japan Synchrotron Radiation Research Institute (JASRI)
Hiroshima University

Key points
• High-resolution measurement focusing on low-concentration magnetic element in diluted magnetic semiconductor
• Understanding of the electronic state of magnetic element, which was difficult with conventional techniques, and clarification of microscopic mechanism of ferromagnetism in diluted magnetic semiconductor
• Possibility of designing materials for high-performance diluted magnetic semiconductors by clarifying roles of magnetic element

Diluted magnetic semiconductors*1 have attracted much attention in spintronics, which exploits the properties of magnets for electronics indispensable in industry.  These semiconductors have both electrical properties of a semiconductor and magnetic properties of a doped magnetic element.  Ga1-xMnxAs (GaMnAs) is a typical diluted magnetic semiconductor obtained by doping a small amount of manganese (Mn) into gallium arsenide*2 (GaAs).  Its practical application as a spintronics material is being examined because it exhibits ferromagnetism at a relatively high temperature.  However, the mechanism of ferromagnetism in GaMnAs has not been conclusively determined, and various physical models have been proposed.

In this study, the microscopic mechanism of ferromagnetism in GaMnAs has been clarified by accurately determining the electronic state of Mn (the magnetic element) using the University-of-Tokyo Synchrotron Radiation Outstation Beamline BL07LSU*4 at SPring-8.*3  The obtained electronic structure of Mn is successfully interpreted by the magnetic polaron model where the introduced career (hole) is weakly bound by the doped trivalent Mn, rather than the Zener's p-d exchange model where the career is itinerant while the doped Mn is divalent.
The research group was led by Masaki Kobayashi (special research fellow) of the School of Engineering, Yoshihisa Harada (associate professor) of the Institute for Solid State Physics, Masaharu Oshima (specially appointed professor) of the Synchrotron Radiation Research Organization, and Masaaki Tanaka (professor) of the School of Engineering, who are all affiliated with the University of Tokyo, in collaboration with JAEA, JASRI, and Hiroshima University.

The achievements of this research will provide a direction for designing materials for diluted magnetic semiconductors that will play a leading role in spintronics.  Details of the achievements were published online in the journal of the American Physical Society, Physical Review Letters, on 12th March 2014.

"Electronic Excitations of Magnetic Impurity State in Diluted Magnetic Semiconductor (Ga,Mn)As"
M. Kobayashi, H. Niwa, Y. Takeda, A. Fujimori, Y. Senba, H. Ohashi, A. Tanaka, S. Ohya, P. N. Hai, M. Tanaka, Y. Harada, and M. Oshima
Physical Review Letters. 112, 107203, Published 12 March 2014


Fig. 1 Crystal structure of Ga1-xMnxAs
Fig. 1 Crystal structure of Ga1-xMnxAs

A doped Mn ion replaces a Ga ion in Ga1-xMnxAs.

Fig. 2 Models for mechanism of ferromagnetism in Ga1-xMnxA
Fig. 2 Models for mechanism of ferromagnetism in Ga1-xMnxAs:
(a) Zener's p-d exchange model and (b) magnetic polaron model

The direction of the arrows in the upper figure indicates the direction of magnets.

Fig. 3	Soft X-ray emission spectrum of GaMnAs and simulation results
Fig. 3 Soft X-ray emission spectrum of GaMnAs and simulation results

The simulation result for Mn3+ (red) is in good agreement with the experimental spectrum (black).

*1 Diluted magnetic semiconductor

A material in which a host semiconductor is doped with a low concentration of magnetic element. Diluted magnetic semiconductors exhibit magnetic properties while retaining the electrical and optical properties of the semiconductor. A combination of these properties is expected to realize new device applications.

*2 Gallium arsenide
A typical compound semiconductor composed of trivalent gallium and pentavalent arsenic. Gallium arsenide strongly absorbs visible light in a certain wavelength range and is widely used for semiconductor devices and lasers.

*3 SPring-8
SPring-8 is a shared synchrotron radiation facility that delivers the world’s highest-brilliance synchrotron radiation. It is owned by RIKEN and located in Harima Science Park City, Hyogo Prefecture, Japan. The name “SPring-8” is derived from “Super Photon ring-8 GeV”. Synchrotron radiation is a type of light radiated when charged particles are forced to bend in magnetic fields. SPring-8 can produce X-rays with a high coherence because of the small size of circulating electron groups and high stability.

*4 University-of-Tokyo Synchrotron Radiation Outstation Beamline BL07LSU
The world's-highest-level soft X-ray undulator beamline is located at the long straight-line section of SPring-8. It is owned by the Materials Science Section of the Synchrotron Radiation Research Organization established directly under the President of the University of Tokyo in May 2006. The beamline has three permanent stations for advanced spectroscopy experiments and a free-port station into which users are allowed to bring their equipment. The shared use of the beamline started in October 2009.

For more information, please contact:
 Synchrotron Radiation Research Organization, The University of Tokyo
   Associate Prof. Yoshihisa Harada