Introduction to tunnel magnetoresistance

Tunnel magnetoresistance (TMR) is a phenomenon in which the resistance of a magnetic tunnel junction (MTJ) changes as a function of the relative orientation of the magnetization of the two ferromagnetic layers separated by an insulating barrier. It arises from the quantum mechanical tunneling of electrons through the barrier, which depends on the spin orientations of the electrons in the ferromagnetic layers. As a result, TMR is a highly sensitive magnetoresistive effect that can be exploited for a variety of applications in magnetoelectronics and spintronics.

Principle of operation

The principle of operation of TMR can be explained by considering a typical MTJ consisting of two thin ferromagnetic layers separated by a thin insulating layer. When a voltage is applied to the MTJ, electrons can tunnel from one ferromagnetic layer to the other through the insulating layer. The probability of tunneling depends on the spin orientations of the electrons in the ferromagnetic layers, which are aligned parallel or antiparallel to each other. When the magnetizations are parallel, the tunneling probability is high and the resistance of the MTJ is low. Conversely, when the magnetizations are antiparallel, the tunneling probability is low and the resistance of the MTJ is high. This change in resistance is the TMR effect.

Applications of tunnel magnetoresistance

TMR has a wide range of applications in magnetic sensors, magnetic random access memory (MRAM), and spintronic devices. For example, TMR sensors are used in hard disk drives to detect the magnetic fields from the data on the disk. MRAM is a type of non-volatile memory that uses TMR to store data, which has advantages over traditional memory technologies such as faster access times, lower power consumption, and higher density. TMR can also be used in spintronic devices such as magnetic tunnel transistors, which can amplify signals and perform logic functions.

Example of tunnel magnetoresistance in technology

One example of TMR in technology is the TMR sensor used in computer hard disk drives. The TMR sensor consists of a small MTJ that is integrated into the read/write head of the disk drive. As the disk spins and data is read, the TMR sensor detects the magnetic fields from the data and converts them into electrical signals that can be processed by the computer. The TMR sensor has revolutionized the storage capacity and performance of hard disk drives, enabling them to store more data in smaller spaces and access it faster than ever before.