470
17 Magnetic Semiconductors
Fig. 17.7 Magnetization
M versus magnetic field H
for Zn 0.935 Mn 0.065 O thin
film at T = 10 and 300 K.
A hysteresis is obvious for
both temperatures
Zn Mn O
0.08
0.04
0
-0.04
-0.08
-3.5
0
3 . 5
7
-7
300K
10K
17.4 Spintronics
Spintronics (as opposed to electronics) is an emerging field that uses the electron spin rather than its
charge for transport, processing and storage of information. Prototype devices are the spin transistor
and the spin LED. A crucial point is spin injection, i.e. the creation of (highly) spin-polarized currents.
It remains to be seen whether spintronics can be developed to its theoretically envisioned potential and
will play a commercially important role in the course of microelectronics. The spin degree of freedom
also promises potential for quantum information processing due to its weak coupling to charge and
phonons and the resulting long dephasing time.
It shall be mentioned here that the magnetization alters also the ‘classical’ transport properties of the
semiconductor. The Hall effect is modified strongly and reflects the magnetic hysteresis, also termed
anomalous Hall effect (AHE).
4 This effect was already discovered by Hall in 1881 for Ni and Co
[1541]; a review of the AHE can be found in [1542]. Also the optical excitation of spin-polarized
carriers in non-magnetic materials causes AHE [1543]. For a magnetic material with topological band
structure, the internal field can be sufficient to evoke the QHE [1544]; this quantum anomalous Hall
effect (QAHE) has been reported for (Bi,Sb) 2 Te 3 :Cr [1545] and MnBi 2 Te 4 [1546].
17.4.1 Spin Transistor
In this device (for regular transistors cf. Chap. 24), spin-polarized electrons are injected from contact 1,
transported through a channel and detected in contact 2. During the transport, the spin rotates (optimally
by π ) such that the electrons cannot enter contact 2 that has the same magnetization as contact 1
(Fig. 17.8). The spin rotation is caused by spin-orbit interaction due to the electric field under the gate
contact. This effect is called the Rashba effect and is purely relativistic [1547]. As channel material, a
semiconductor with strong spin-orbit coupling such as InAs or (In,Ga)Sb is preferable. However, the
use of narrow-gap semiconductors and the increase of spin scattering at elevated temperatures [1548]
make the realization of such a transistor at room temperature difficult.
4 This use of the term ‘anomalous’ should be distinguished from the historical use of ‘anomalous’ Hall effect for the sign
reversal of the Hall voltage for hole conductors.
17 Magnetic Semiconductors
Fig. 17.7 Magnetization
M versus magnetic field H
for Zn 0.935 Mn 0.065 O thin
film at T = 10 and 300 K.
A hysteresis is obvious for
both temperatures
Zn Mn O
0.08
0.04
0
-0.04
-0.08
-3.5
0
3 . 5
7
-7
300K
10K
17.4 Spintronics
Spintronics (as opposed to electronics) is an emerging field that uses the electron spin rather than its
charge for transport, processing and storage of information. Prototype devices are the spin transistor
and the spin LED. A crucial point is spin injection, i.e. the creation of (highly) spin-polarized currents.
It remains to be seen whether spintronics can be developed to its theoretically envisioned potential and
will play a commercially important role in the course of microelectronics. The spin degree of freedom
also promises potential for quantum information processing due to its weak coupling to charge and
phonons and the resulting long dephasing time.
It shall be mentioned here that the magnetization alters also the ‘classical’ transport properties of the
semiconductor. The Hall effect is modified strongly and reflects the magnetic hysteresis, also termed
anomalous Hall effect (AHE).
4 This effect was already discovered by Hall in 1881 for Ni and Co
[1541]; a review of the AHE can be found in [1542]. Also the optical excitation of spin-polarized
carriers in non-magnetic materials causes AHE [1543]. For a magnetic material with topological band
structure, the internal field can be sufficient to evoke the QHE [1544]; this quantum anomalous Hall
effect (QAHE) has been reported for (Bi,Sb) 2 Te 3 :Cr [1545] and MnBi 2 Te 4 [1546].
17.4.1 Spin Transistor
In this device (for regular transistors cf. Chap. 24), spin-polarized electrons are injected from contact 1,
transported through a channel and detected in contact 2. During the transport, the spin rotates (optimally
by π ) such that the electrons cannot enter contact 2 that has the same magnetization as contact 1
(Fig. 17.8). The spin rotation is caused by spin-orbit interaction due to the electric field under the gate
contact. This effect is called the Rashba effect and is purely relativistic [1547]. As channel material, a
semiconductor with strong spin-orbit coupling such as InAs or (In,Ga)Sb is preferable. However, the
use of narrow-gap semiconductors and the increase of spin scattering at elevated temperatures [1548]
make the realization of such a transistor at room temperature difficult.
4 This use of the term ‘anomalous’ should be distinguished from the historical use of ‘anomalous’ Hall effect for the sign
reversal of the Hall voltage for hole conductors.