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2 Basic Elements of Spintronics
electron population that could be well described by Maxwell–Boltzmann statistics.
Under the application of a suitable electrical bias across the interface, electrons
flow takes place from the paramagnetic semiconductor into the half-metallic ferromagnetic contact. It can be well understood that electrons incoming from the bulk
of the semiconductor are spin unpolarized and that the half-metallic ferromagnet
accepts only majority spins electrons in the half-metal (say, up-spin electrons). This
implies that minority spin electrons (here down-spin electrons) cannot pass through
the ferromagnet, rather scatter into it. Therefore, a cloud of down-spin electrons must
accumulate at the interface between the half-metallic ferromagnet and the paramagnetic semiconductor. This in turn results in the formation of a local spin-dipole
configuration close to the interface. Now, at a critical current magnitude, the semiconductor region near the interface becomes completely depleted of a particular
species of electrons, which are actually majority spins electrons in the half-metallic
contact. Such phenomenon has been referred to as ‘spin blockade’ by Pershin and Di
Ventra. Furthermore, spin flip scattering events (discussed in detail in Chap. 3) at the
interface are neglected in this case, and the interface is modelled as a planar junction.
The one-dimensional drift-diffusion equations are used to study spin extraction from
the paramagnetic semiconductor.
2.12 Field- and Heat-Driven Spintronics Effect
Spintronic devices depend on a systematic generation, transportation and detection
of spin currents. These functionalities can be executed by different spintronic effects.
Spin–orbit interaction has two significant consequences: (i) it can exert torques and
thereby induce a precession of the electron spin and (ii) it can regulate the orbital
motion of electrons leading to the transport of spin angular momentum. The latter
includes the spin-dependent Hall effect and the spin-dependent Seebeck effect. Spintronic phenomena may be field-driven or heat-driven. Field-driven effects are spindependent Hall effect (e.g., the anomalous Hall effect, the spin Hall effect and inverse
Hall effect), magnetoresistance effects (such as the giant, tunnelling and spin Hall
magnetoresistance), spin pumping and its inverse. Significantly, their realization is
not to be limited to DC driving currents only. It can also be extended to free-space
terahertz electromagnetic radiation-driven ultrafast charge current.
Let us discuss two phenomena: (i) field-driven Hall effect and (ii) heat-driven
Seebeck effect in detail.
2.12.1 Field-Driven Hall Effect
Background
As a prelude, we may mention the history of the Hall effect in 1879 after the
discovery of a small transverse voltage appeared across a current carrying thin metal
2 Basic Elements of Spintronics
electron population that could be well described by Maxwell–Boltzmann statistics.
Under the application of a suitable electrical bias across the interface, electrons
flow takes place from the paramagnetic semiconductor into the half-metallic ferromagnetic contact. It can be well understood that electrons incoming from the bulk
of the semiconductor are spin unpolarized and that the half-metallic ferromagnet
accepts only majority spins electrons in the half-metal (say, up-spin electrons). This
implies that minority spin electrons (here down-spin electrons) cannot pass through
the ferromagnet, rather scatter into it. Therefore, a cloud of down-spin electrons must
accumulate at the interface between the half-metallic ferromagnet and the paramagnetic semiconductor. This in turn results in the formation of a local spin-dipole
configuration close to the interface. Now, at a critical current magnitude, the semiconductor region near the interface becomes completely depleted of a particular
species of electrons, which are actually majority spins electrons in the half-metallic
contact. Such phenomenon has been referred to as ‘spin blockade’ by Pershin and Di
Ventra. Furthermore, spin flip scattering events (discussed in detail in Chap. 3) at the
interface are neglected in this case, and the interface is modelled as a planar junction.
The one-dimensional drift-diffusion equations are used to study spin extraction from
the paramagnetic semiconductor.
2.12 Field- and Heat-Driven Spintronics Effect
Spintronic devices depend on a systematic generation, transportation and detection
of spin currents. These functionalities can be executed by different spintronic effects.
Spin–orbit interaction has two significant consequences: (i) it can exert torques and
thereby induce a precession of the electron spin and (ii) it can regulate the orbital
motion of electrons leading to the transport of spin angular momentum. The latter
includes the spin-dependent Hall effect and the spin-dependent Seebeck effect. Spintronic phenomena may be field-driven or heat-driven. Field-driven effects are spindependent Hall effect (e.g., the anomalous Hall effect, the spin Hall effect and inverse
Hall effect), magnetoresistance effects (such as the giant, tunnelling and spin Hall
magnetoresistance), spin pumping and its inverse. Significantly, their realization is
not to be limited to DC driving currents only. It can also be extended to free-space
terahertz electromagnetic radiation-driven ultrafast charge current.
Let us discuss two phenomena: (i) field-driven Hall effect and (ii) heat-driven
Seebeck effect in detail.
2.12.1 Field-Driven Hall Effect
Background
As a prelude, we may mention the history of the Hall effect in 1879 after the
discovery of a small transverse voltage appeared across a current carrying thin metal