Spintronics

Abstract

The field of spintronics is introduced and differentiated from magnetoelectronics. Augmentation of the capabilities of nanoelectronics by the addition of two spin degrees of freedom to the preexisting two charge degrees of freedom is explained. The spin degrees of freedom can also be used alone to create functional devices. The role of spintronics as a bridge between semiconductor ICs and magnetic storage is elucidated. The technologically recognized spintronic device working on giant magnetoresistance effect is compared with normal magnetoresistance. The operation of magnetic tunnel junction devices for providing high magnetoresistance ratios is described. Performance of MRAM is compared with SRAM, DRAM and flash memory devices. Besides fast access, the capability of spin transfer torque RAM to decrease the write current in comparison to MRAM is indicated. The main application areas of spintronics in computer hard disks and magnetic random access memory devices are highlighted.

Review Exercises

• 11.1 What is the full form of ‘spintronics ’? What are the other names by which ‘spintronics’ is called?

• 11.2 Define spintronics. What is the difference between spintronics and magnetoelectronics ?

• 11.3 Name two intrinsic properties of electron besides its spin. What are the two allowed values of electron spin and how are they represented?

• 11.4 Explain how does spintronics extend the capability of semiconductor nanoelectronics by adding two spin degrees of freedom to the existing two charge degrees of freedom. What advantages accrue from the additional degrees of freedom?

• 11.5 How does spintronics act as a bridge between semiconductor integrated circuits and magnetic storage devices? Elaborate.

• 11.6 What are the problems faced in incorporating magnetic materials used in spintronics into semiconductor nanoelectronics?

• 11.7 What are the application areas of metallic spintronics and semiconductor spintronics? Which of the two branches of spintronics is still in infant stage?

• 11.8 Name a spintronic device, which is established industrially. Where is it used?

• 11.9 What is magnetoresistance effect? What is the meaning of ‘anisotropic magnetoresistance (AMR) ’? What is the extent of change in resistance?

• 11.10 How does giant magnetoresistance effect differ from normal magnetoresistance effect? How much does the degree of resistance change produced in GMR differ from that in AMR ? Is GMR restricted only to films of thickness in the nanoscale?

• 11.11 Explain the origin of GMR effect in terms of the parallel/antiparallel alignment of adjacent ferromagnetic layers.

• 11.12 Does GMR effect only take place in nanostructures fabricated by molecular beam epitaxy? Name a less expensive method of producing such nanostructures.

• 11.13 A magnetoresistive device can provide a much higher magnetoresistance ratio than the GMR device. What is this device called? What value of the ratio is achieved with this device?

• 11.14 Describe how are the different layers of a magnetic tunnel junction arranged. How is the magnetization of one layer fixed? How does the free layer respond to an applied magnetic field? What is the effect on magnetoresistance of this device in a magnetic field?

• 11.15 What is the main application of spintronics? What are the three stages in the operational scheme of spintronic devices?

• 11.16 How is information written in MRAM? How is it read from MRAM? How does MRAM compare in performance with respect to SRAM , DRAM and flash memory?

• 11.17 What is meant by spin polarized current ? Where is it used? In what ways is STT-RAM superior to MRAM ?

• 11.18 What kind of tasks the metallic spintronic devices cannot perform? Why is it necessary to develop semiconductor spintronic devices?