Working Principle of Giant Magnetoresistance (GMR) Magnetic Field Sensor

The GMR effect is a magnetoresistance effect discovered in 1988. Since it is more than an order of magnitude larger than the traditional magnetoresistance effect, it is named Giant Magnetoresistor (GMR).

1. Principle of Giant Magnetoresistance (GMR), see Figure 1.

The GMR effect comes from the different spin states of current-carrying electrons and the different effects of the magnetic field, which leads to changes in resistance. This effect can only be observed in nanoscale film structures. With special structural design, this effect can also be adjusted to meet various performance requirements.

Conductive output characteristics in high resistance state during antiferromagnetic coupling (external magnetic field is 0), resistance: R1/2

When the magnetic multilayer film is in saturation state (the magnetic moments of adjacent magnetic layers are distributed in parallel) due to an external magnetic field, the resistance is in a low resistance state, and the conductive output characteristic is: R2*R3/(R2+R3), R2>R1>R3
Figure 1. Using the two-stream model to explain the mechanism of GMR

2. Giant Magneto-Resistor (GMR) Sensor Principle, see Figure 2. The GMR sensor uses four GMRs to form a Wheatstone bridge structure, which can reduce the impact of the external environment on the stability of the sensor output and increase the sensitivity of the sensor. When working, the "current input end" in the figure is connected to a 5V~20V regulated voltage, and the "output end" outputs a voltage signal under the action of an external magnetic field.

Figure 2 (1): Principle of the Wheatstone bridge in magnetic field sensor applications

Figure 2 (2): Changes in R1 and R2 in a Wheatstone bridge under an external magnetic field

3. Performance of giant magnetoresistance (GMR) sensor, see Figure 3 and Table 1.

Figure 3 shows the performance curve of the giant magnetoresistance (GMR) sensor in the external field, indicating that the sensor has good linearity in the magnetic field range of ±200Oe.

Figure 3: Performance curve of giant magnetoresistance (GMR) under an applied magnetic field

Table 1 Comparison of performance of giant magnetoresistance (GMR) sensors from various companies

4. Product Instructions

a. As an active device, the giant magnetoresistance (GMR) sensor must provide a 5~20V DC power supply for its operation . Moreover, the stability of the power supply directly affects the test accuracy of the sensor, so it is required to be provided by a regulated power supply; overvoltage power supply should also be avoided during use; b. As a high-precision magnetic sensitive sensor, the giant magnetoresistance (GMR) sensor also has certain requirements for the magnetic environment in which it is used. The model selection should be determined according to the magnetic field size of the use environment; c. The sensitivity of the giant magnetoresistance (GMR) sensor to the magnetic field is related to the direction. The sensitive axis marked on its external structure is the direction in which the sensor is most sensitive to the magnetic field, see Figure 4. When it is not parallel, the sensitivity decreases, and the relationship is Sθ=S0COSθ , where Sθ is the sensitivity when the angle between the magnetic field direction and the sensor sensitive axis is θ, and S0 is the sensitivity when the magnetic field direction is parallel to the sensor sensitive axis.

Figure 4: Giant magnetoresistance (GMR) sensor structure and wiring diagram

d. When the output characteristic is an even function with respect to the external magnetic field, an external bias magnetic field is required when the sensor is used for measurement. Ideally, the magnitude of the bias magnetic field is 1/2 of the magnetic field in the linear range of the sensor.