5.6 Possible Applications of Spin-Transfer Torques
143
Nevertheless, even smaller values of critical currents are desirable. For instance,
critical currents of 0.1 mA could possibly control magnetic bits employing
minimum-area silicon CMOS transistors. This in turn could feasibly materialize
the realization of very dense memory circuits.
5.6.2 Spin-Transfer Torque-Driven Microwave Sources
and Oscillators
As already mentioned in Sect. 5.3, dynamical magnetic modes, corresponding to
microwave frequency, can be excited by DC spin-transfer torques. Recently, such
experiments are under rigorous investigations for the use of high-speed signal
processing, as nanoscale microwave sources, oscillators and amplifiers. The spintransfer torque devices, executing precession motion, may be implemented as
sources and detectors for wireless chip-to-chip communications (Kiselev et al. 2003;
Krivorotov et al. 2005).
5.7 Conclusions
In this chapter, we have introduced the concept and definition of spin-transfer torque.
Furthermore, we have discussed spin-transfer torque effect in layer structures, both
for single and double ferromagnetic (FM) layers. We have also addressed interesting
topic like spin-transfer torque-driven magnetization dynamics, both in absence and
presence of spin-transfer torque. Few experimental results, such as point contact
device, multilayer nanopillar etc., have also been discussed in this case. We have
also taken into account some possible applications of spin-transfer torques, such as
magnetic random access memory, spin-transfer torque-driven microwave sources
and oscillators etc., in this chapter. However, in an attempt to employ spin-transfer
torque-based magnetic sensor in current-perpendicular-to-the-plane GMR magnetic
read heads, spin-transfer torques has been found to generate noise and reduce the
effectiveness of the sensor. Therefore, a detailed understanding of spin-transfer torque
excitations is indeed important for reduction of these hazardous effects. Presently, a
lot of research is actively going on in this field of STT.
5.8 Exercises
1. What is spin-transfer torque process?
2. Why is the spin-transfer torque limited to nanoscale samples?
3. What are the different processes used to identify the mechanism of spin-transfer
torque in the nanoscale samples?
143
Nevertheless, even smaller values of critical currents are desirable. For instance,
critical currents of 0.1 mA could possibly control magnetic bits employing
minimum-area silicon CMOS transistors. This in turn could feasibly materialize
the realization of very dense memory circuits.
5.6.2 Spin-Transfer Torque-Driven Microwave Sources
and Oscillators
As already mentioned in Sect. 5.3, dynamical magnetic modes, corresponding to
microwave frequency, can be excited by DC spin-transfer torques. Recently, such
experiments are under rigorous investigations for the use of high-speed signal
processing, as nanoscale microwave sources, oscillators and amplifiers. The spintransfer torque devices, executing precession motion, may be implemented as
sources and detectors for wireless chip-to-chip communications (Kiselev et al. 2003;
Krivorotov et al. 2005).
5.7 Conclusions
In this chapter, we have introduced the concept and definition of spin-transfer torque.
Furthermore, we have discussed spin-transfer torque effect in layer structures, both
for single and double ferromagnetic (FM) layers. We have also addressed interesting
topic like spin-transfer torque-driven magnetization dynamics, both in absence and
presence of spin-transfer torque. Few experimental results, such as point contact
device, multilayer nanopillar etc., have also been discussed in this case. We have
also taken into account some possible applications of spin-transfer torques, such as
magnetic random access memory, spin-transfer torque-driven microwave sources
and oscillators etc., in this chapter. However, in an attempt to employ spin-transfer
torque-based magnetic sensor in current-perpendicular-to-the-plane GMR magnetic
read heads, spin-transfer torques has been found to generate noise and reduce the
effectiveness of the sensor. Therefore, a detailed understanding of spin-transfer torque
excitations is indeed important for reduction of these hazardous effects. Presently, a
lot of research is actively going on in this field of STT.
5.8 Exercises
1. What is spin-transfer torque process?
2. Why is the spin-transfer torque limited to nanoscale samples?
3. What are the different processes used to identify the mechanism of spin-transfer
torque in the nanoscale samples?