tunneling magneto-resistive (hard disk) (TMR)
The TMR(Tunneling Magneto-Resistive) mechanism, a technique used in magnetic field sensors, involves a tunneling effect based on quantum physics. This effect occurs in layer systems with at least two ferromagnetic layers with an insulating layer in between.
The TMR effect can be explained by the fact that in extremely thin structures, on the order of molecules, even the thinnest insulators located between two conducting layers allow electrons to pass through. In tunneling magneto-resistance, a highly thin insulator is located between two ferromagnetic layers and changes its resistance value with the orientation of the magnetic field.
The advantage of this technique over the other magneto-resistive techniques, Anisotropic Magneto-Resistive( AMR) and Giant Magneto-Resistive( GMR), is the extremely small size of TMR sensors, which have edge lengths in the micrometer range.