1063-7397/01/3004- $25.00 © 2001 MAIK “Nauka /Interperiodica”
0258
Russian Microelectronics, Vol. 30, No. 4, 2001, pp. 258–260. Translated from Mikroelektronika, Vol. 30, No. 4, 2001, pp. 302–304.
Original Russian Text Copyright © 2001by Randoshkin, Saletskii, Sysoev, Chervonenkis.
The speed of magnetooptic controlled transparen-
cies (MOCTs) to a great extent depends on the switch-
ing rate in single-domain cells made in bismuth-substi-
tuted single-crystal garnet ferrite (BSGF) films [1]. The
conventional switching mechanism is treated in terms
of domain-wall movement [2–11]. Obviously, the
MOCT speed can be improved by increasing the wall
velocity. The wall velocity can be raised by introducing
rhombic magnetic anisotropy, increasing the gyromag-
netic ratio near the point of angular momentum com-
pensation, or by applying a permanent magnetic field in
the MOCT plane [12]. Also, the speed of MOCTs can
be improved if switching takes place through magneti-
zation rotation [13, 14].
In this work, still another way of improving the
MOCT speed is considered. It combines a new config-
uration of a single-domain magnetooptic cell (Fig. 1)
and the known switching mechanism that involves the
movement of end domain walls [1, 8]. In the usual cell
configuration, switching occurs when the domain wall
travels a distance that equals the cell dimension. For the
new configuration (Fig. 1), this distance equals the
thickness
h
c
of the magnetooptic film in the cell.
For the practical use of MOCTs, single-domain
cells must have a size of ~100
µ
m. Such cells can
readily be created in BSGF films of thickness
h
~
10
µ
m
with a relatively low saturation magnetization
4
π
M
s
(and, hence, with a large characteristic length). How-
ever, single-domain cells of such a size may have a
greater
4
π
M
s
if the thickness of the film is small (
h
~
0.1
µ
m) [15–17]. It is essential that, as the magnetiza-
tion of BSGF films grows, so does the specific Faraday
rotation. The magnetooptic figure of merit necessary
for the effective MOCT operation is provided if a laser
with a wavelength of
λ
= 0.44
µ
m is used as a light
source [2].
The mechanism of switching through the movement
of end domain walls is realized by producing a layer
with lower magnetic anisotropy in a BSGF film [1, 8].
Such a layer usually forms spontaneously at the initial
stage of epitaxial growth [1, 18, 19]. Another way to
produce the layer is the use of controllable ion implan-
tation [1, 6, 7].
To achieve the ultimate MOCT speed, single-
domain cells of the new configuration (Fig. 1) should
have a high velocity of domain walls (
≥
1000 m/s). In
the practical range of magnetic fields
H
, such a value is
observed at the point of angular momentum compensa-
tion in
(Bi, Gd, Tm)
3
(Fe, Ga)
5
O
12
(111) films (Fig. 2,
curve
1
) and in
(Bi, Y, Lu, Pr)
3
(Fe, Ga)
5
O
12
(210) films
with rhombic anisotropy (Fig. 2, curve
2
). However, in
the former films, the domain wall velocity drastically
drops even at a distance of ~10 K from the point of
angular momentum compensation [17]. With the new
cell configuration (Fig. 1), this disadvantage becomes
insignificant, since, for nonuniform
(Bi, Gd, Tm)
3
(Fe,
Ga)
5
O
12
films, a temperature range where the wall
velocity reaches 1000 m/s or more greatly extends [20].
To increase the saturation magnetization of films with
angular momentum compensation, some
Tm
3+
ions
must be replaced by rare-earth magnetic ions with a
higher magnetic moment (such as by Ho
3+
or
Dy
3+
ions)
[20]. Such a replacement, however, decreases the wall
mobility.
In
(Bi, Y, Lu, Pr)
3
(Fe, Ga)
5
O
12
films with rhombic
magnetic anisotropy, the wall motion is unsteady and,
accordingly, the wall velocity is anisotropic.
An end domain wall in a single-domain cell (Fig. 1)
forms due to the motion of a wave of magnetic moment
breaking [1]. The formation time depends only on the
rise time of a switching pulse. For
h
c
= 0.1
µ
m and
V
=
1000 m/s, the switching time of the cell in Fig. 1 was
estimated at 0.1 ns.
On Increasing the Switching Rate
in a Single-Domain Magnetooptic Cell
V. V. Randoshkin*, A. M. Saletskii**, N. N. Sysoev**, and A. Ya. Chervonenkis*
* Mordovian State University, Magnitooptoelektronika Joint Laboratory of the Institute of General Physics,
Russian Academy of Sciences, Bol’shevistskaya ul. 68, Saransk, 430000 Russia
** Department of Physics, Moscow State University, Vorob’evy gory, 119899 Russia
Received June 2, 2000
Abstract
—A single-domain cell for magnetooptic controlled transparencies that improves their speed is sug-
gested.
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