Light and Spins in III-V Ferromagnetic Semiconductors
Hiro Munekata
Tokyo Institute of Technology, Yokohama, Japan
e-mail : [email protected]
III-V ferromagnetic semiconductors (FS), such as (In,Mn)As [1,2] and (Ga,Mn)As [3,4],
are the semiconductor alloys which contain a large amount of magnetic ions (1020-1021 cm-3)
in the III-V semiconductor epitaxial films. This was realized by carrying out the epitaxial
growth at substrate temperature of Ts  200 – 300 C which is far below the values used for
the conventional epitaxial growth (Ts  400 - 6000 C). Studies carried out for more than a
decade have revealed that various transition metal elements could be incorporated beyond the
solubility limit in all III-V host crystals by properly choosing the growth conditions.
For the mid- and narrow gap III-V FS, Mn ions that occupy the group III sub-lattice sites
are electrically and magnetically active and form the spin-selective, acceptor states near the
top of the valence band. This spin-selective character causes both Mn ions and valence bands
to be spin polarized when electrons (or holes) are shared between the acceptor and valence
bands (hole-mediated ferromagnetism). This situation makes it possible to manipulate Mn
spins through carrier spins by the optical excitation.
Since the first demonstration of optical inducement of ferromagnetic order in (In,Mn)As
in 1997 [5], we have been pursuing optical manipulation of ferromagnetism. One such
striking example is the experiment of magnetization rotation in a ferromagnetic p-(Ga,Mn)As
layer induced by the optical spin injection using circularly polarized light [6,7]. Other
interesting experiments are the optically-induced precession of magnetization [8] and
ultra-fast demagnetization [9] in femto- and pico-second time regime. These studies would
lead us to the understanding of direct pathways of energy and momentum transfer among
electron, lattice, spin subsystems, and development of knowledge for the ultrafast
manipulation of magnetism.
[1] H. Munekata, et al., Phys. Rev. Lett. 63, 1849 (1989).
[2] H. Munekata, et al., J. Cryst. Growth 111, 1011 (1991).
[3] H. Ohno, et al., Appl. Phys. Lett. 69, 363 (1996).
[4] T. Hayashi, et al., J. Cryst. Growth 175/176, 1063 (1997).
[5] S. Koshihara, et al., Phys. Rev. Lett. 78, 4617 (1997).
[6] A. Oiwa, et al., Phys. Rev. Lett. 88, 137202 (2002).
[7] Y. Mitsumori, et al., Phys. Rev. B 69, 033203 (2004).
[8] A. Oiwa, et al., J. Superconductivity: Incorp. Novel Magnetism 18, 9 (2005).
[9] J. Wang, et al., Phys. Rev. Lett. 95, 167401 1-4 (2005).
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