Theoretical Prediction of Ferromagnetism
in Semiconductor Dot Array
Hiroyuki Tamura, Kenji Shiraishi, and Hideaki
Takayanagi
Materials Science Laboratory
Ferromagnetism in non-magnetic semiconductor
dot arrays is theoretically predicted. It
has been known that a ferromagnetic spin-state
is induced by electron-electron interactions
in a certain type of lattice structure having
dispersion-less band, so called flat band
[1]. However, there has been no clear evidence
of observing flat-band ferromagnetism so
far, because it is difficult to synthesize
or fabricate materials in such a way that
the flat band is formed. The present work
proposes that the use of semiconductor-dot
array (Fig. 1) would be the most promising
way to realize flat-band ferromagnets (Fig.
2) [2].
Ferromagnets of non-magnetic semiconductor-dots
have several great advantages in application.
First, one can make ferromagnets just by
utilizing existing LSI fabrication techniques.
For example, conventional MOS transistors
and magnetic devices, such as sensors or
memories, made by semiconductor-dot ferromagnets
can be fabricated on the same silicon chip.
This allows us to reduce the chip size and
the number of fabrication processes. Second,
one can modulate the electron filling by
changing the gate voltage, and ferromagnetic
and paramagnetic states can be freely switched
by changing the gate voltage. This controllability
of magnetic states can lead to the possibility
of ultra-fast switching devices or ultra-sensitive
sensors made by the proposed semiconductor-dot
ferromagnets.
[1] E. H. Lieb, Phys. Rev. Lett. 62 (1989) 1201.
[2] H. Tamura, K. Shiraishi, and H. Takayanagi,
Jpn. J. Appl. Phys. 39 (2000) L241.
Fig. 1. Schematic two-dimensional dot array
exhibiting ferromagnetism.
Fig. 2. Example of flat-band (in the middle
of three subbands).
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