7 Current-Induced Dynamics of Chiral Magnetic Structures
173
7.5.4 Magnetization Dynamics of Three-Dimensional
Hopfions
As magnetic hopfions in chiral magnets have only recently been proposed theoretically, see Sect. 7.3, their dynamics are a field that is still much under investigation.
In thin films of chiral magnets with perpendicularly magnetized surfaces, hopfions
are predicted to be stabilized due to geometric confinement. The magnetic texture
of the hopfion is then fixed by the DMI such that only translational modes can be
activated easily. For such a setup, it was shown theoretically that the STT-driven
H = 1 hopfion behaves like a skyrmionium, i.e., it moves like a two-dimensional
soliton, straight along the applied current without any Hall angle [83].
More complex dynamics are predicted for three-dimensional frustrated magnets:
Here, the translation in all spatial dimensions and rotation around all axes are zero
modes. It was shown in a theoretical study by Liu et al. [84] that the STT-driven
H = 1 hopfion indeed rotates while moving with the current, adjusting such that
its skyrmionium-like cross-section aligns perpendicular to the current. Moreover,
inside the hopfion, regions with positive and negative skyrmion charge Q are present
which are subject to opposite skyrmion Hall angles. As a consequence, the STTdriven hopfion either inflates or deflates, dependent on the direction of the current.
For a detailed description of the dynamics, featuring also a discussion in the Thiele
framework, we refer to [84].
7.6 Potential Applications
Based on the very rich playground of spintronics with chiral magnetic structures, several potential applications have been proposed over the recent years. In the following
we will briefly introduce some of them.
7.6.1 Storage and Logic Technologies
Magnetic racetrack. The central idea behind the racetrack is that information is
encoded by magnetic bits which are placed in a one-dimensional shift register device.
Data can be accessed or written at a particular point of the nanowire. It has the
great advantage that instead of moving mechanical parts, only the magnetic bits are
moved, e.g., by spin-currents. In the classically suggested version [85, 86], the bits are
magnetic domains, separated by domain walls. For the racetrack based on magnetic
skyrmions [87], the state of a bit can be represented by the presence or absence of a
skyrmion. The latter has the advantage to circumvent the impact of edge roughness
in the nanowire, as skyrmions opposed to domain walls do not necessarily touch the
edge. However, it has also some disadvantages. In particular, the skyrmion Hall effect
173
7.5.4 Magnetization Dynamics of Three-Dimensional
Hopfions
As magnetic hopfions in chiral magnets have only recently been proposed theoretically, see Sect. 7.3, their dynamics are a field that is still much under investigation.
In thin films of chiral magnets with perpendicularly magnetized surfaces, hopfions
are predicted to be stabilized due to geometric confinement. The magnetic texture
of the hopfion is then fixed by the DMI such that only translational modes can be
activated easily. For such a setup, it was shown theoretically that the STT-driven
H = 1 hopfion behaves like a skyrmionium, i.e., it moves like a two-dimensional
soliton, straight along the applied current without any Hall angle [83].
More complex dynamics are predicted for three-dimensional frustrated magnets:
Here, the translation in all spatial dimensions and rotation around all axes are zero
modes. It was shown in a theoretical study by Liu et al. [84] that the STT-driven
H = 1 hopfion indeed rotates while moving with the current, adjusting such that
its skyrmionium-like cross-section aligns perpendicular to the current. Moreover,
inside the hopfion, regions with positive and negative skyrmion charge Q are present
which are subject to opposite skyrmion Hall angles. As a consequence, the STTdriven hopfion either inflates or deflates, dependent on the direction of the current.
For a detailed description of the dynamics, featuring also a discussion in the Thiele
framework, we refer to [84].
7.6 Potential Applications
Based on the very rich playground of spintronics with chiral magnetic structures, several potential applications have been proposed over the recent years. In the following
we will briefly introduce some of them.
7.6.1 Storage and Logic Technologies
Magnetic racetrack. The central idea behind the racetrack is that information is
encoded by magnetic bits which are placed in a one-dimensional shift register device.
Data can be accessed or written at a particular point of the nanowire. It has the
great advantage that instead of moving mechanical parts, only the magnetic bits are
moved, e.g., by spin-currents. In the classically suggested version [85, 86], the bits are
magnetic domains, separated by domain walls. For the racetrack based on magnetic
skyrmions [87], the state of a bit can be represented by the presence or absence of a
skyrmion. The latter has the advantage to circumvent the impact of edge roughness
in the nanowire, as skyrmions opposed to domain walls do not necessarily touch the
edge. However, it has also some disadvantages. In particular, the skyrmion Hall effect