26
2 Basic Elements of Spintronics
from the paramagnet. It should be noted that if a ferromagnetic detector transmits
only one kind of spin, then the spin detection efficiency is 100%. In analogy to optics,
sometimes spin detectors are referred to as ‘spin analysers’.
2.3 Spin Generation and Injection
In spintronics, generation of spin-polarized electrons plays a pivotal role for making
spintronic devices (Ohno et al. 1999; Jedema et al. 2001; Appelbaum et al. 2007;
Saikin 2004; Yu et al. 2012; Suzuki et al. 2009; Tang et al. 2002; Schmidt et al. 2000;
Wu and Jiang 2010). Several methods are taken up for generation of spin-polarized
electron in non-magnetic (NM) materials (see Fig. 2.2) (Hirohataa et al. 2020). They
are (i) spin injection from a ferromagnetic (FM), (ii) a magnetic field, (iii) an electric
field, (iv) electromagnetic wave introduction, (v) Zeeman splitting, (vi) spin motive
force, (vii) a thermal gradient and (viii) mechanical rotation. The frequently used
method is spin injection from a ferromagnetic material. Here, conventional ferromagnetic metals, half-metallic ferromagnets and dilute magnetic semiconductors (DMS)
are attached to a non-magnetic metal or semiconductor through an ohmic contact or
a tunnel barrier. Though a stray field at the edge of a FM can induce a population
difference in spin-polarized electrons in a non-magnetic material, yet it is not easy to
control due to its well-defined edge shape. An electric field can initiate the movement
of spin-polarized electrons in a NM material towards a desired direction based on
spin Hall effects. Circularly polarized light stimulates spin-polarized electrons in a
semiconductor. Through reverse effect, circularly polarized light can be produced
by a spin-polarized electron current. This can also be extended for spin generation
by electromagnetic waves. Thermal gradient-driven spin Seebeck and Nernst effects
can also generate spin-polarized carrier. In a DMS, spin imbalance can be induced
at the Fermi level through Zeeman splitting.
Fig. 2.2 Different methods
for generation of
spin-polarized electron in
non-magnetic (NM)
materials (Taken from
Hirohata et al. 2020)
2 Basic Elements of Spintronics
from the paramagnet. It should be noted that if a ferromagnetic detector transmits
only one kind of spin, then the spin detection efficiency is 100%. In analogy to optics,
sometimes spin detectors are referred to as ‘spin analysers’.
2.3 Spin Generation and Injection
In spintronics, generation of spin-polarized electrons plays a pivotal role for making
spintronic devices (Ohno et al. 1999; Jedema et al. 2001; Appelbaum et al. 2007;
Saikin 2004; Yu et al. 2012; Suzuki et al. 2009; Tang et al. 2002; Schmidt et al. 2000;
Wu and Jiang 2010). Several methods are taken up for generation of spin-polarized
electron in non-magnetic (NM) materials (see Fig. 2.2) (Hirohataa et al. 2020). They
are (i) spin injection from a ferromagnetic (FM), (ii) a magnetic field, (iii) an electric
field, (iv) electromagnetic wave introduction, (v) Zeeman splitting, (vi) spin motive
force, (vii) a thermal gradient and (viii) mechanical rotation. The frequently used
method is spin injection from a ferromagnetic material. Here, conventional ferromagnetic metals, half-metallic ferromagnets and dilute magnetic semiconductors (DMS)
are attached to a non-magnetic metal or semiconductor through an ohmic contact or
a tunnel barrier. Though a stray field at the edge of a FM can induce a population
difference in spin-polarized electrons in a non-magnetic material, yet it is not easy to
control due to its well-defined edge shape. An electric field can initiate the movement
of spin-polarized electrons in a NM material towards a desired direction based on
spin Hall effects. Circularly polarized light stimulates spin-polarized electrons in a
semiconductor. Through reverse effect, circularly polarized light can be produced
by a spin-polarized electron current. This can also be extended for spin generation
by electromagnetic waves. Thermal gradient-driven spin Seebeck and Nernst effects
can also generate spin-polarized carrier. In a DMS, spin imbalance can be induced
at the Fermi level through Zeeman splitting.
Fig. 2.2 Different methods
for generation of
spin-polarized electron in
non-magnetic (NM)
materials (Taken from
Hirohata et al. 2020)