4 - Effects

Hall effect is widely and conventionally used in several types of magnetic sensors. Assuming that l>>w, the charge carriers of the electric current through the conducting or semiconducting sample will flow parallel to the length at the center of the device. Therefore, a perpendicular electric field to the current direction arises to compensate the Lorentz force acting on the carriers moving perpendicularly to the magnetic field. The Hall voltage appearing on the Hall electrodes is: where I is the current, B the magnetic field, t the thickness of the sample, and R_H the Hall-constant. The Hall-voltage is improved for a material with high mobility, low conductivity (e.g. GaAs, InSb) and thin device geometry.

The resistance of solid-state devices is changed with the applied magnetic field and this is called megnetoresistive effect. There are two causes of the resistance change, i.e., the change of the resistivity of the material and the change of the current path under magnetic field. In a magnetic sensor using this basis, such as a magnetoresistor, both effects contribute the change in the resistance value. The former effect requires high mobility and InSb is the only candidate among semiconductor materials. On the other hand, in ferromagnetic materials, such as Ni-Co and Ni-Fe, the second type magnetoresistive effect is commonly used because of their spontaneous magnetization in a relatively low magnetic field. The current path is changed according to their domain structure redistribution under varying magnetic field.

The dimensions of ferromagnetic materials is changed with the applied magnetic field and this is called megnetostrictive effect. The dimension is changed according to their domain structure redistribution (shiftig and rotating) under varying magnetic field. Each material has a magnetostrictive coefficient, which is defined as fraction of lenght change between zero and maximum magnetization (saturation).

The magnetoelastic effect is the inverse of the magnetostrictive effect. Permeability changes as mechanical deformation is applied on ferroelectric materials. This can be measured different way, eg. change in inductivity, voltage, or current.