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8 Terahertz Spintronics
picosecond time scale, which is much faster than what can be achieved through
conventional charge-based electronics).
8.4 Why Do We Need Terahertz Spintronics?
Spintronic read head sensors and magnetic random access memory (MRAM) have
already impacted on multibillion dollar industry due to its intriguing features like
non-volatility, fast switching, low switching energy and capabilities of increased integration densities compared to the conventional semiconductor devices. But recently,
the field effect transistor (FET) is reaching its cutoff frequency up to 1 THz. On
the other hand, optical fiber communication as well as LAN (local area network)
are about to reach terahertz bandwidth. Hence, spintronic technology, operating at
gigahertz range, urgently needs to transfer its functionalities from GHz to THz.
The use of spintronics in terahertz range may be of twofold. It may (i) speed up
existing computing and (ii) bring a paradigm shift incorporating three-dimensional
chip structures or using plasmons or magnons for computing. Though integration
densities (number of transistor per unit area) are still increasing, yet frequency
clocking remains almost stagnant (at few gigahertz) in last decades. THz spintronics
can pave the way of closer synchronization between processing and memory clock
by combining ultrafast optics and spintronics. THz spintronics will not be confined
with ultrafast computing only; it will extend its periphery in the field of imaging,
sensing, security, bio-medical science and many more due to its intriguing features.
Terahertz spintronics will be feasible if we observe that the fundamental concepts
and phenomena of spintronics also work at terahertz frequency domain. Fortunately, observations are favourable towards the implementation of spin-dependent
phenomena in THz scale and are given below.
• Giant magnetoresistance (GMR), for which the Nobel Prize was awarded, has
been observed in THz frequency.
• Mott’s two current model is functional at THz frequency.
• Operation of spin transfer torque (STT) at THz frequency domain has been
reported.
• MRAMs are also operative at THz frequency through MTJ (magnetic tunnel
junction) based bits.
• THz fields can access elementary spin couplings (e.g., to phonons).
• Spin Hall effect and spin Seebeck effects are operative up to 10 s of THz.
• Inverse spin Hall effect is still operative in THz frequencies.
It has also been reported that the power of spintronic terahertz emitters is at par
with GaP- and ZnTe-based electronic THz emitters. However, the spintronic terahertz emitters have much larger bandwidth 1–30 THz. Recently, it has been reported
that the magnetization direction of emitter can comfortably modify the polarization
of terahertz pulse, which accelerates the development of powerful terahertz near field
sources. One important advantage of spintronic-based THz emitters is the possibility
8 Terahertz Spintronics
picosecond time scale, which is much faster than what can be achieved through
conventional charge-based electronics).
8.4 Why Do We Need Terahertz Spintronics?
Spintronic read head sensors and magnetic random access memory (MRAM) have
already impacted on multibillion dollar industry due to its intriguing features like
non-volatility, fast switching, low switching energy and capabilities of increased integration densities compared to the conventional semiconductor devices. But recently,
the field effect transistor (FET) is reaching its cutoff frequency up to 1 THz. On
the other hand, optical fiber communication as well as LAN (local area network)
are about to reach terahertz bandwidth. Hence, spintronic technology, operating at
gigahertz range, urgently needs to transfer its functionalities from GHz to THz.
The use of spintronics in terahertz range may be of twofold. It may (i) speed up
existing computing and (ii) bring a paradigm shift incorporating three-dimensional
chip structures or using plasmons or magnons for computing. Though integration
densities (number of transistor per unit area) are still increasing, yet frequency
clocking remains almost stagnant (at few gigahertz) in last decades. THz spintronics
can pave the way of closer synchronization between processing and memory clock
by combining ultrafast optics and spintronics. THz spintronics will not be confined
with ultrafast computing only; it will extend its periphery in the field of imaging,
sensing, security, bio-medical science and many more due to its intriguing features.
Terahertz spintronics will be feasible if we observe that the fundamental concepts
and phenomena of spintronics also work at terahertz frequency domain. Fortunately, observations are favourable towards the implementation of spin-dependent
phenomena in THz scale and are given below.
• Giant magnetoresistance (GMR), for which the Nobel Prize was awarded, has
been observed in THz frequency.
• Mott’s two current model is functional at THz frequency.
• Operation of spin transfer torque (STT) at THz frequency domain has been
reported.
• MRAMs are also operative at THz frequency through MTJ (magnetic tunnel
junction) based bits.
• THz fields can access elementary spin couplings (e.g., to phonons).
• Spin Hall effect and spin Seebeck effects are operative up to 10 s of THz.
• Inverse spin Hall effect is still operative in THz frequencies.
It has also been reported that the power of spintronic terahertz emitters is at par
with GaP- and ZnTe-based electronic THz emitters. However, the spintronic terahertz emitters have much larger bandwidth 1–30 THz. Recently, it has been reported
that the magnetization direction of emitter can comfortably modify the polarization
of terahertz pulse, which accelerates the development of powerful terahertz near field
sources. One important advantage of spintronic-based THz emitters is the possibility