# Magneto Resistor – Definition, Working, Types, Uses & Characteristics

Magneto Resistor

What is a Magneto Resistor?

Magneto resistor is a type of resistor whose resistance changes when an external magnetic field is applied. In other words, the flow of electric current through the magneto resistor changes when an external magnetic field is applied to it. Magnetic field is the region present around a magnetic object within which other objects experience an attractive or repulsive force.

History of the Magneto Resistor

Magneto Resistor was found by Sir William Thomson that, when the iron pieces were kept in magnetic feild, their electrical resistance somehow changed when the direction of magnetic feild with respect to the current flow through them changed. This effect was found when he experimented with nickel too. Thus a new effect or phenomenon was introduced to the world and it was named magneto-resistance. This effect was then further studied and a new type of variable resistor was formed. This resistor would have its electrical resistance vary with the magnetic field strength around it. The flow of the current through this resistor also changes with change in magnetic force applied to it.

As you already know that magnetic field is a vector quantity meaning, it us specified in both direction and magnitude, just as a current.

What is the Symbol of Magneto Resistor?

Schematically, in circuit diagram the magneto resistance is represented by the symbol shown below. The arrow through the resistor symbol signifies a variable resistor, while “x” below it denotes that the variable resistor used is “magneto resistor”

Working Principal of Magneto Resistor

How magneto resistors work?

The working of the magneto resistor is quite easy; it is based on the effect already mentioned: the magneto resistance.

The magneto resistors that are placed in the magnetic field will experience a change in resistance. When the strength of the magnetic field is increased, the resistance of magneto resistors also increases. On the other hand, when the strength of magnetic field is reduced, the resistance of magneto resistors decreases. This change in resistance is caused by the magneto resistive effect.

In the absence of magnetic field, the charges carriers in the material move in a straight path. Therefore, electric current flows in a straight path. When the magnetic field is applied to the material, the magnetic forces cause the mobile charge carriers (free electrons) to change their direction from direct path to indirect path. This increases the length of electric current path.

Hence, large number of free electrons collides with the atoms and loses their energy in the form of heat and only a small number of free electrons flow through the conductive path. The small number of free electrons moving from one place to another place carries the electric current. Therefore, the resistance of the material increases with increasing magnetic field.

Effects of Magneto Resistors

Magneto resistive effect is the property of some materials, which causes them to change their resistance under the presence of magnetic field. This magneto resistive effect occurs in materials such as semiconductors, non-magnetic metals, and magnetic metals.

An Irish mathematical physicist and engineer William Thomson first discovered this magneto resistive effect in 1856. He observed that resistance of the pieces of iron increased when the electric current is flowing in the same direction as the magnetic force or magnetic field and the resistance is decreased when the electric current is flowing at 90° to the magnetic field or magnetic force.

After that, he performed the same experiment with nickel and he found that the resistance of the nickel is affected in the same manner but the magnitude of this magnetic field was much greater than before. This effect is called Anisotropic Magneto Resistance (AMR).

Types of Magneto Resistors

According to the types of magneto-resistance effect, magneto resistor are also categorized into three groups. Lets discuss about them in brief.

(1) Giant Magneto Resistance (GMR)
(2) Extraordinary Magneto Resistance (EMR)
(3) Tunnel Magneto Resistance (TMR)

Giant Magneto Resistance (GMR)
Albert Fert and Peter Grunberg discovered the Giant Magneto Resistance (GMR) in 1988. This effect is observed in the ferromagnetic materials. The resistance of the ferromagnetic material is depends on the whether the magnetization of adjacent ferromagnetic layers are aligned parallel or anti-parallel. The resistance is high for the ferromagnetic layers with anti-parallel alignment whereas the resistance is low for the ferromagnetic layers with parallel alignment.

Extraordinary Magneto Resistance (EMR)
The extraordinary magneto resistive effect is discovered in 2000. The magnetic field effect of EMR (Extraordinary Magneto Resistance) is much greater than (GMR) Giant Magneto Resistance. The EMR effect occurs in semiconductor metal hybrid systems when a transverse magnetic field is applied.

In the absence of magnetic field, the resistance of semiconductor metal hybrid system is very low whereas in the presence of strong magnetic field, the resistance of semiconductor metal hybrid system is high.

Tunnel Magneto Resistance (TMR)
M. Julliere discovered the Tunnel Magneto Resistance (TMR) in 1975. The Tunnel Magneto Resistance (TMR) occurs in Magnetic Tunnel Junction (MTJ). Magnetic Tunnel Junction (MTJ) is a component consists of two ferromagnets separated by an insulator. The electrons will flow from one ferromagnet to another ferromagnet through the tunnel barrier or insulator. The amount of electric current or charge carriers flowing through the tunnel is depends on orientation of magnetizations.

Uses and Applications of Magneto Resistor

Owing to their dependency on the magnetic field, these magneto resistors find use in magnetic field sensing devices. These include, electromagnetic compass, magnetometers which measure magnetic field intensity and direction, position sensors and ferrous metal detection. Position sensors can be angle , rotary or linear position sensors. They also find use in bio sensors and hard disk drives.

Short & Important Notes on Magneto Resistors

Magneto-resistors: variable resistor whose resistance depends on magnetic field strength.
Direction if current = direction of magnetic force, then magnetic field intensity is high. This means the resistance is high.
Resistance of magneto-resistor is directly proportional to the strength of magnetic field.
This effect is called magneto resistance, discovered by Sir William Thomson
Three types of magneto resistance effect: Giant magneto resistance, Extraordinary magneto resistance and tunnel magneto resistance.
The characteristic curve shows the dependency of resistance on the magnetic field strength.
Most prominent uses include those involving magnetic field sensors, like electromagnetic compass, magnetometers etc. Also used in bio sensors and hard disk drives.