6
1 An Overview of Spintronics
1.4 Evolution of Spintronics
Let us go back into the history of spintronics. It emerged from the discoveries of
the spin-dependent electron transport phenomena in solid-state devices in 1980s.
Such discovery is about the injection of spin-polarized electron from a ferromagnetic to a normal metal by Johnson and Silsbee (1985) and the giant magnetoresistance by Albert Fert (Baibich et al. 1988) and Peter Grünberg (1988) (Baibich
et al. 1989), independently. The Nobel Prize in Physics 2007 was awarded jointly
to Albert Fert and Peter Grünberg for this discovery of giant magnetoresistance.
Furthermore, beginning of spintronics can be tracked back from the pioneering
ferromagnet/superconductor tunnelling experiments, carried out by Meservey and
Tedrow and also from the early experiments performed on magnetic tunnel junctions
by Julliere in 1970s (Julliere 1975). The concept of incorporation of semiconductors
for spintronics applications was introduced through the theoretical proposal of a spin
field effect transistor by Datta and Das (1990). Subsequently in spintronics, a new
field of research, merging the technology of semiconductor and magnetism, has been
developed. In this attempt, spin information of the electrons is intended to be utilized
for extending the functionalities of the common transistor. This leads to the development that lead to ‘going beyond transistor-based circuits’, hence prompting a model
shift from the electronically driven to an entirely magnetically controlled digital
logic. Based on magnetoresistive elements, the first design concepts for magnetic
logic AND and OR gates have been proposed. This constituted the basic building
blocks for the magnetic random access memory. Noteworthy, the non-volatile logic
output of magnetic elements poses an immense advantage in comparison to that
of conventional semiconductor-based electronics technology. This advent of technology is expected to decrease the consumption of power by several orders of magnitude. In 2012, IBM scientists observed and mapped the creation of persistent spin
helices of synchronized electrons. Such observation of spin helices persisting for
more than a nanosecond is actually a 30-fold increase from the previously observed
results (Walser et al. 2012). This is even longer than the duration of a modern
processor clock cycle. This finding opens new avenues of research for employing
electron spins in information processing.
1.4.1 History of Spin
Stern–Gerlach Experiment
In 1925, Ralph De LaerKronig, George Uhlenbeck and Samuel Goudsmit, based on
the anomalous Zeeman effect, postulated that along with orbital angular momentum,
an electron possesses an additional angular momentum, arising out of the spinning
motion about its own axis. Such spinning motion of electron is much like earth
1 An Overview of Spintronics
1.4 Evolution of Spintronics
Let us go back into the history of spintronics. It emerged from the discoveries of
the spin-dependent electron transport phenomena in solid-state devices in 1980s.
Such discovery is about the injection of spin-polarized electron from a ferromagnetic to a normal metal by Johnson and Silsbee (1985) and the giant magnetoresistance by Albert Fert (Baibich et al. 1988) and Peter Grünberg (1988) (Baibich
et al. 1989), independently. The Nobel Prize in Physics 2007 was awarded jointly
to Albert Fert and Peter Grünberg for this discovery of giant magnetoresistance.
Furthermore, beginning of spintronics can be tracked back from the pioneering
ferromagnet/superconductor tunnelling experiments, carried out by Meservey and
Tedrow and also from the early experiments performed on magnetic tunnel junctions
by Julliere in 1970s (Julliere 1975). The concept of incorporation of semiconductors
for spintronics applications was introduced through the theoretical proposal of a spin
field effect transistor by Datta and Das (1990). Subsequently in spintronics, a new
field of research, merging the technology of semiconductor and magnetism, has been
developed. In this attempt, spin information of the electrons is intended to be utilized
for extending the functionalities of the common transistor. This leads to the development that lead to ‘going beyond transistor-based circuits’, hence prompting a model
shift from the electronically driven to an entirely magnetically controlled digital
logic. Based on magnetoresistive elements, the first design concepts for magnetic
logic AND and OR gates have been proposed. This constituted the basic building
blocks for the magnetic random access memory. Noteworthy, the non-volatile logic
output of magnetic elements poses an immense advantage in comparison to that
of conventional semiconductor-based electronics technology. This advent of technology is expected to decrease the consumption of power by several orders of magnitude. In 2012, IBM scientists observed and mapped the creation of persistent spin
helices of synchronized electrons. Such observation of spin helices persisting for
more than a nanosecond is actually a 30-fold increase from the previously observed
results (Walser et al. 2012). This is even longer than the duration of a modern
processor clock cycle. This finding opens new avenues of research for employing
electron spins in information processing.
1.4.1 History of Spin
Stern–Gerlach Experiment
In 1925, Ralph De LaerKronig, George Uhlenbeck and Samuel Goudsmit, based on
the anomalous Zeeman effect, postulated that along with orbital angular momentum,
an electron possesses an additional angular momentum, arising out of the spinning
motion about its own axis. Such spinning motion of electron is much like earth