2.12 Field- and Heat-Driven Spintronics Effect
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quantum interference device microscope, with high spatial resolution, might enable
us for this kind of measurement by measuring local magnetic fields.
Physics of spin Hall effect (SHE)
The phenomenon spin Hall effect is related to the spin accumulation at opposite edges
of a given slab. This seems to imply the generation of a current flowing perpendicular
to electrical charge current. This effect may occur in both magnetic and non-magnetic
materials. It is well known that when electrical current flows through a non-magnetic
material it becomes magnetic. Some semi-classically defined mechanisms, such as
intrinsic, skew scattering and side-jump scattering causes the generation of spinpolarized current, which is the origin of SHE. In order to understand these mechanisms, we have to discuss the types of perpendicular current, which are generated by
SHE and inverse SHE (ISHE). Two types of perpendicular currents are as follows:
1. Band current (intrinsic current)
2. Scattering current (extrinsic current).
1. Band current: This type of current occurs when the number of electrons moving
in one direction is different from the number of electrons moving in the opposite
direction. This happens when the probability of an electron scattering in one direction is different from the scattering probability in opposite direction. This is caused
by the external electric field. For instance, under the application of electric field in
x-direction, the scattering probability of electrons to a state (k x + k x , k y , k z ) is larger
than to a state (k x − Δk x , k y , k z ). Such direction-dependent scattering probability
is due to the conduction electrons gaining/losing energy when they are accelerating/decelerating in the electric field. Ordinary Hall effect and the current along
electric field are the examples of band current.
2. Scattering current: In case of a conduction electron, after it suffers a scattering, in
addition to the movement direction, its spatial position is also getting changed as well.
Scattering current occurs when shift in position of the electron after it encounters
scattering is different for two opposite directions. Consequently, the electron is found
to be constantly shifted in one direction after consecutive scatterings. This is actually
the case when because of the presence of an external field the scattering probability
of an electron in one position is different from the scattering probability in opposite
position. As an example, we may mention that under the application of an electric
field in x-direction, scattering probability to a state (x + Δx, y, z) is larger than to a state
(x − Δx, y, z). Consequently, the electrons are supposed to be continuously drifted
along x-direction. The reason for spacial dependence of the scattering probability is
that the energy of quantum states gradually becomes large along the electric field.
Therefore, scattering of an electron to a lower energy state has a lower probability.
Tunnelling current, hoping current and current in a low conductivity metal are the
examples of such scattering current.
Coming back to the discussion of SHE, it essentially gives the description of the
creation of spin-polarized current. As discussed in last paragraph, there are only two
65
quantum interference device microscope, with high spatial resolution, might enable
us for this kind of measurement by measuring local magnetic fields.
Physics of spin Hall effect (SHE)
The phenomenon spin Hall effect is related to the spin accumulation at opposite edges
of a given slab. This seems to imply the generation of a current flowing perpendicular
to electrical charge current. This effect may occur in both magnetic and non-magnetic
materials. It is well known that when electrical current flows through a non-magnetic
material it becomes magnetic. Some semi-classically defined mechanisms, such as
intrinsic, skew scattering and side-jump scattering causes the generation of spinpolarized current, which is the origin of SHE. In order to understand these mechanisms, we have to discuss the types of perpendicular current, which are generated by
SHE and inverse SHE (ISHE). Two types of perpendicular currents are as follows:
1. Band current (intrinsic current)
2. Scattering current (extrinsic current).
1. Band current: This type of current occurs when the number of electrons moving
in one direction is different from the number of electrons moving in the opposite
direction. This happens when the probability of an electron scattering in one direction is different from the scattering probability in opposite direction. This is caused
by the external electric field. For instance, under the application of electric field in
x-direction, the scattering probability of electrons to a state (k x + k x , k y , k z ) is larger
than to a state (k x − Δk x , k y , k z ). Such direction-dependent scattering probability
is due to the conduction electrons gaining/losing energy when they are accelerating/decelerating in the electric field. Ordinary Hall effect and the current along
electric field are the examples of band current.
2. Scattering current: In case of a conduction electron, after it suffers a scattering, in
addition to the movement direction, its spatial position is also getting changed as well.
Scattering current occurs when shift in position of the electron after it encounters
scattering is different for two opposite directions. Consequently, the electron is found
to be constantly shifted in one direction after consecutive scatterings. This is actually
the case when because of the presence of an external field the scattering probability
of an electron in one position is different from the scattering probability in opposite
position. As an example, we may mention that under the application of an electric
field in x-direction, scattering probability to a state (x + Δx, y, z) is larger than to a state
(x − Δx, y, z). Consequently, the electrons are supposed to be continuously drifted
along x-direction. The reason for spacial dependence of the scattering probability is
that the energy of quantum states gradually becomes large along the electric field.
Therefore, scattering of an electron to a lower energy state has a lower probability.
Tunnelling current, hoping current and current in a low conductivity metal are the
examples of such scattering current.
Coming back to the discussion of SHE, it essentially gives the description of the
creation of spin-polarized current. As discussed in last paragraph, there are only two