Chapter 4
Tunnelling Magnetoresistance (TMR)
4.1 Introduction on Tunnelling Magnetoresistance
4.1.1 Introductory Note
In the previous chapter, we have discussed the effect of spin-dependent scattering on
the electric current passing through the magnetic multilayer films to produce GMR.
Similarly, the magnetic field dependence of the electrical current passing through the
magnetic tunnel junctions (MTJs) is another subject of great interest.
4.1.2 What Is Magnetic Tunnel Junction (MTJ)?
Magnetic tunnel junction (MTJ) is basically two ferromagnetic layers, separated by
a non-magnetic insulating layer.
4.1.3 What Is Tunnelling Magnetoresistance (TMR)?
In order to obtain the GMR effect, the non-magnetic spacer layer between two ferromagnetic layers is supposed to be a conducting material, i.e., metallic. This means
GMR is an all-metallic device structure. However, if the metallic spacer layer is
replaced by an insulating layer, as in the case of MTJ, the conduction electrons
originating from one ferromagnetic electrode would undergo quantum tunnelling
across the insulating barrier to reach another ferromagnetic electrode. This means
that quantum mechanical tunnelling would be the conduction mechanism in this
case. More subtle feature is that such tunnelling process has been found to be spindependent and depends on the relative angle between the magnetization of those two
ferromagnetic layers. This phenomenon was first observed by Julliere in a Fe/Ge/Co
© Springer Nature Singapore Pte Ltd. 2021
P. Dey and J. N. Roy, Spintronics,
https://doi.org/10.1007/978-981-16-0069-2_4
103
Tunnelling Magnetoresistance (TMR)
4.1 Introduction on Tunnelling Magnetoresistance
4.1.1 Introductory Note
In the previous chapter, we have discussed the effect of spin-dependent scattering on
the electric current passing through the magnetic multilayer films to produce GMR.
Similarly, the magnetic field dependence of the electrical current passing through the
magnetic tunnel junctions (MTJs) is another subject of great interest.
4.1.2 What Is Magnetic Tunnel Junction (MTJ)?
Magnetic tunnel junction (MTJ) is basically two ferromagnetic layers, separated by
a non-magnetic insulating layer.
4.1.3 What Is Tunnelling Magnetoresistance (TMR)?
In order to obtain the GMR effect, the non-magnetic spacer layer between two ferromagnetic layers is supposed to be a conducting material, i.e., metallic. This means
GMR is an all-metallic device structure. However, if the metallic spacer layer is
replaced by an insulating layer, as in the case of MTJ, the conduction electrons
originating from one ferromagnetic electrode would undergo quantum tunnelling
across the insulating barrier to reach another ferromagnetic electrode. This means
that quantum mechanical tunnelling would be the conduction mechanism in this
case. More subtle feature is that such tunnelling process has been found to be spindependent and depends on the relative angle between the magnetization of those two
ferromagnetic layers. This phenomenon was first observed by Julliere in a Fe/Ge/Co
© Springer Nature Singapore Pte Ltd. 2021
P. Dey and J. N. Roy, Spintronics,
https://doi.org/10.1007/978-981-16-0069-2_4
103