What is Magnetoresistor？

Definition: When the resistance of certain metals and semiconductor materials changes in the presence of a magnetic field, this phenomenon is referred to as the magnetoresistance effect. The components that exhibit this effect are called magnetoresistors. Put simply, a magnetoresistor is a type of resistor whose resistance value fluctuates with the strength and direction of an external magnetic field.

Magnetoresistors play a crucial role in detecting the presence of a magnetic field, measuring its strength, and determining the direction of the magnetic force. They are typically fabricated from semiconductor materials such as indium antimonide or indium arsenide, which possess unique electrical properties that make them highly sensitive to magnetic fields.

Working Principle of Magnetoresistor

The operation of a magnetoresistor is based on the principle of electrodynamics. According to this principle, the force acting on a current-carrying conductor in a magnetic field can change the direction of the current. When there is no magnetic field, the charge carriers in the magnetoresistor move along a straight path.

However, in the presence of a magnetic field, the direction of the current changes and flows in the opposite direction. The circuitous path of the current increases the mobility of the charge carriers, which leads to collisions. These collisions result in the loss of energy in the form of heat, and this heat causes an increase in the resistance of the magnetoresistor. Only a very small magnitude of current flows in the magnetoresistor due to the presence of a limited number of free electrons.

The deflection of electrons in a magnetoresistor depends on their mobility. The mobility of charge carriers in semiconductor materials is higher compared to that in metals. For instance, the mobility of indium arsenide or indium antimonide is approximately 2.4 m²/Vs.

Characteristics of Magnetoresistor

The sensitivity of a magnetoresistor depends on the strength of the magnetic field. The characteristic curve of a magnetoresistor is shown in the figure below.

In the absence of a magnetic field, the magnetization of the magnetoresistor element is zero. As the magnetic field begins to increase slightly, the resistance of the material approaches the value corresponding to point b. The presence of the magnetic field causes the magnetoresistor element to rotate by an angle of 45º.

With a further increase in the magnetic field strength, the curve reaches a saturation point, denoted by point C. The magnetoresistive element typically operates either at the initial state (point O) or near point b. When operating at point b, it exhibits a linear characteristic.

Types of Magnetoresistors

Magnetoresistors can be categorized into three main types:

Giant Magnetoresistance (GMR)

In the Giant Magnetoresistance effect, the resistance of the magnetoresistor is significantly reduced when its ferromagnetic layers are aligned parallel to each other. Conversely, when these layers are in an antiparallel alignment, the resistance increases dramatically. The structural configuration of a GMR device is illustrated in the figure below.

Extraordinary Magnetoresistance (EMR)

In the case of Extraordinary Magnetoresistance, the resistance of the metal shows a distinct behavior. In the absence of a magnetic field, the resistance is relatively high. However, when a magnetic field is applied, the resistance drops significantly, demonstrating a notable change in electrical properties in response to the magnetic influence.

Tunnel Magnetoresistor (TMR)

In a Tunnel Magnetoresistor, current conduction occurs in a unique way. The current traverses from one ferromagnetic electrode, passing through an insulating layer. The amount of current that tunnels through this insulating barrier is highly dependent on the relative orientation of the magnetization in the ferromagnetic electrodes. Different magnetization directions can lead to significant variations in the magnitude of the tunneling current, making this property crucial for various applications that rely on precise control and detection of magnetic states.

A relatively large current will flow when the magnetization directions of the electrodes are parallel to each other. Conversely, an antiparallel arrangement of the magnetization directions significantly increases the resistance between the layers.