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J. Masell and K. Everschor-Sitte
hinders the straight motion of the skyrmion through the nanowire. To enhance the
speed of the magnetic data, (synthetic) antiferromagnetic instead of ferromagnetic
materials have been studied within the recent years. An antiferromagnetic coupling
would also resolve the problem with the skyrmion Hall effect as in this case the forces
in the direction perpendicular to the current direction typically cancel [115, 116].
Moreover, similar devices with closely packed skyrmions or other similar solitons
have been suggested as the information encoded in not well-defined inter-skyrmion
distances is very fragile [88].
Bubble memory. In the 1970s and 1980s, before magnetic racetracks were discussed, memory devices exploiting magnetic bubbles have been commercially available. These are non-volatile two-dimensional shift register memories that exploit the
magnetic field-driven motion of small magnetized areas—the bubbles [89, 90].
Magnetic transistor. Transistors as key elements for controlling integrated circuits
and logic devices have also been proposed to be implemented based on magnetic textures, such as a domain wall based transistor [91] or a skyrmion based transistor [92]
These exploit the gate-voltage controlled motion of the magnetic nanostructures.
Magnetic logic. Another key field in spintronics is the idea to create magnetic-based
logic gates [93]. This is, on the one hand, done by studying nano-magnetic logic,
where nano-magnetic islands with a uniaxial-anisotropy represent the zero and one
state based on their orientation with respect to this anisotropy direction, e.g., “up”
and “down”. The other idea is to send signals through an appropriately shaped device,
which represent the logical gates. This includes magnonic logic [94] as well as logic
based on chiral magnetic states such as skyrmions. An example of the latter was
suggested by Zhang et al. [95] which exploits the possibility to convert spin-torque
driven skyrmions into domain walls in narrow wires. In a convention where a logical
1 or 0 is represented by the presence or absence of a skyrmion, respectively, an
OR gate and AND gate have been simulated by properly designing the width of the
narrow wires.
Magnetic nano-oscillators. Oscillators exploit the system’s natural time scale and
responses to external sources to provide a tunable frequency source. In magnetic
texture based systems, these oscillators are naturally on the nano-scale and exploit, for
example, the current-driven self oscillation of domain walls [96] or skyrmions [97].
While for ferromagnets the frequencies are in the GHz regime and can be tuned,
e.g., by an externally applied magnetic field, they can be in the THz regime for
antiferromagnetic materials, thereby bridging the THz gap.
7.6.2 Unconventional Spintronics-Based Computing
Schemes
Within the recent years, more and more unconventional computational paradigms
are being explored. Based on their low-energy consumption, compact nanometer
J. Masell and K. Everschor-Sitte
hinders the straight motion of the skyrmion through the nanowire. To enhance the
speed of the magnetic data, (synthetic) antiferromagnetic instead of ferromagnetic
materials have been studied within the recent years. An antiferromagnetic coupling
would also resolve the problem with the skyrmion Hall effect as in this case the forces
in the direction perpendicular to the current direction typically cancel [115, 116].
Moreover, similar devices with closely packed skyrmions or other similar solitons
have been suggested as the information encoded in not well-defined inter-skyrmion
distances is very fragile [88].
Bubble memory. In the 1970s and 1980s, before magnetic racetracks were discussed, memory devices exploiting magnetic bubbles have been commercially available. These are non-volatile two-dimensional shift register memories that exploit the
magnetic field-driven motion of small magnetized areas—the bubbles [89, 90].
Magnetic transistor. Transistors as key elements for controlling integrated circuits
and logic devices have also been proposed to be implemented based on magnetic textures, such as a domain wall based transistor [91] or a skyrmion based transistor [92]
These exploit the gate-voltage controlled motion of the magnetic nanostructures.
Magnetic logic. Another key field in spintronics is the idea to create magnetic-based
logic gates [93]. This is, on the one hand, done by studying nano-magnetic logic,
where nano-magnetic islands with a uniaxial-anisotropy represent the zero and one
state based on their orientation with respect to this anisotropy direction, e.g., “up”
and “down”. The other idea is to send signals through an appropriately shaped device,
which represent the logical gates. This includes magnonic logic [94] as well as logic
based on chiral magnetic states such as skyrmions. An example of the latter was
suggested by Zhang et al. [95] which exploits the possibility to convert spin-torque
driven skyrmions into domain walls in narrow wires. In a convention where a logical
1 or 0 is represented by the presence or absence of a skyrmion, respectively, an
OR gate and AND gate have been simulated by properly designing the width of the
narrow wires.
Magnetic nano-oscillators. Oscillators exploit the system’s natural time scale and
responses to external sources to provide a tunable frequency source. In magnetic
texture based systems, these oscillators are naturally on the nano-scale and exploit, for
example, the current-driven self oscillation of domain walls [96] or skyrmions [97].
While for ferromagnets the frequencies are in the GHz regime and can be tuned,
e.g., by an externally applied magnetic field, they can be in the THz regime for
antiferromagnetic materials, thereby bridging the THz gap.
7.6.2 Unconventional Spintronics-Based Computing
Schemes
Within the recent years, more and more unconventional computational paradigms
are being explored. Based on their low-energy consumption, compact nanometer