The anomalous Hall effect (AHE) is a phenomenon in ferromagnetic materials where a transverse voltage (Hall voltage) appears even in the absence of an external magnetic field. This effect arises due to intrinsic properties of the material, particularly spin–orbit coupling and magnetization.
How It Differs from the Ordinary Hall Effect:
- In the ordinary Hall effect, a magnetic field applied perpendicular to a current-carrying conductor causes charge carriers to deflect sideways, producing a voltage across the sample.
- In the anomalous Hall effect, this transverse voltage occurs spontaneously in ferromagnetic materials due to internal magnetic ordering and spin-dependent scattering.
Underlying Mechanisms:
- Intrinsic mechanism: Due to the Berry curvature in the material’s electronic band structure — an effect of spin–orbit interaction acting like a magnetic field in momentum space.
- Extrinsic mechanisms:
- Skew scattering: Asymmetric scattering of electrons off impurities depending on spin orientation.
- Side jump: Spin–orbit interaction causes a sideways displacement during scattering.
Importance and Applications:
- Offers insights into topological properties and spin–orbit physics.
- Crucial for spintronics, where electronic devices exploit spin in addition to charge.
- Helps characterize magnetic materials and their transport behavior.
The AHE is a striking example of how quantum mechanical effects and magnetic order can influence electron motion even without external fields.