266
M. Becherer
volume, all magnetic fields i.e. the stray field from the neighboring dot and the
externally applied Zeeman clocking field H z superpose.
Now, two scenarios are possible: (2) The stray field of the left magnet is adding
to the Zeeman field, it supports to overcome the pinning barrier and the DW is
immediately propagating through the magnet, fully reversing it. By contrast, the
second scenario is shown in (3). The stray field of the left magnet is opposing the
Zeeman field. Hence, the DW is not propagating as the energy barrier is not overcome.
Consequently, the magnet is not switched back to the parallel state. In Fig. 3b, the
effect of magnetic coupling is additionally visualized by means of a hysteresis loop of
the switched magnet. By choosing a perpendicular field amplitude H s which equals
the switching field of a single magnet, a symmetric clocking window opens, where
computation (=anti-parallel ordering) takes place. Additionally, a switching field
distribution is sketched in the graph, which is due to thermally activated broadening
of the switching field when overcoming the energy barrier (see e.g. [26, 27]). Please
note, as long as field-coupling from the neighboring magnet is strong enough, reliable
switching (from the parallel to the anti-parallel state) or suppression of switching
(in case the states are already anti-parallel) is achieved. The unique behavior of
unidirectional signal flow in an external Zeeman-field, is achieved by side-irradiation
of magnetic islands with a focused ion beam. There have been related experiments,
where a ‘ratchet-like’ behavior was achieved in an irradiated domain-wall conduit
by Franken et al. [28].
In order to sum up the basic principle of NML operation, the ANC can be described
as summing point for all generated stray fields in close vicinity and the externally
applied Zeeman field. Depending on the leftmost neighbor, the magnet will switch
into the anti-parrallel configuration, due to the ANC close to the edge of the island.
Assuming that the ANC is infinitesimally small, magnetic islands can be described
by lumped elements. Stray fields are calculated by the shape and the areal magnetic
moment of the islands and those fields will act on the ANC, where the logic decision
is made. The nonlinear switching behavior (highly non-linear hysteresis loop) will
result in a sudden reversal of the magnetic domain, starting with a DW from the ANC
and spreading over the whole magnetic island.
2.3 Major Building Blocks of Planar 2D pNML
By the introduced technique of localized ion irradiation for ANC creation and
superposition of stray fields in the ANC, a 2D pNML family of logic devices has
been demonstrated. The major building blocks are depicted as schematic layout
and summarized in Fig. 4. The devices are briefly discussed in the following. The
simplest structure is the binary state, an island with magnetization pointing parallel/antiparallel to the film normal. The logic values ‘0’ and ‘1’ are assigned to it.
A chain of magnetic islands with unidirectional data flow in a spatially homogeneous clocking field (Zeeman field)—often referred to as inverter chain— has been
demonstrated in Breitkreutz et al. in [23], Eichwald et al. in [29] and Kiermaier et
M. Becherer
volume, all magnetic fields i.e. the stray field from the neighboring dot and the
externally applied Zeeman clocking field H z superpose.
Now, two scenarios are possible: (2) The stray field of the left magnet is adding
to the Zeeman field, it supports to overcome the pinning barrier and the DW is
immediately propagating through the magnet, fully reversing it. By contrast, the
second scenario is shown in (3). The stray field of the left magnet is opposing the
Zeeman field. Hence, the DW is not propagating as the energy barrier is not overcome.
Consequently, the magnet is not switched back to the parallel state. In Fig. 3b, the
effect of magnetic coupling is additionally visualized by means of a hysteresis loop of
the switched magnet. By choosing a perpendicular field amplitude H s which equals
the switching field of a single magnet, a symmetric clocking window opens, where
computation (=anti-parallel ordering) takes place. Additionally, a switching field
distribution is sketched in the graph, which is due to thermally activated broadening
of the switching field when overcoming the energy barrier (see e.g. [26, 27]). Please
note, as long as field-coupling from the neighboring magnet is strong enough, reliable
switching (from the parallel to the anti-parallel state) or suppression of switching
(in case the states are already anti-parallel) is achieved. The unique behavior of
unidirectional signal flow in an external Zeeman-field, is achieved by side-irradiation
of magnetic islands with a focused ion beam. There have been related experiments,
where a ‘ratchet-like’ behavior was achieved in an irradiated domain-wall conduit
by Franken et al. [28].
In order to sum up the basic principle of NML operation, the ANC can be described
as summing point for all generated stray fields in close vicinity and the externally
applied Zeeman field. Depending on the leftmost neighbor, the magnet will switch
into the anti-parrallel configuration, due to the ANC close to the edge of the island.
Assuming that the ANC is infinitesimally small, magnetic islands can be described
by lumped elements. Stray fields are calculated by the shape and the areal magnetic
moment of the islands and those fields will act on the ANC, where the logic decision
is made. The nonlinear switching behavior (highly non-linear hysteresis loop) will
result in a sudden reversal of the magnetic domain, starting with a DW from the ANC
and spreading over the whole magnetic island.
2.3 Major Building Blocks of Planar 2D pNML
By the introduced technique of localized ion irradiation for ANC creation and
superposition of stray fields in the ANC, a 2D pNML family of logic devices has
been demonstrated. The major building blocks are depicted as schematic layout
and summarized in Fig. 4. The devices are briefly discussed in the following. The
simplest structure is the binary state, an island with magnetization pointing parallel/antiparallel to the film normal. The logic values ‘0’ and ‘1’ are assigned to it.
A chain of magnetic islands with unidirectional data flow in a spatially homogeneous clocking field (Zeeman field)—often referred to as inverter chain— has been
demonstrated in Breitkreutz et al. in [23], Eichwald et al. in [29] and Kiermaier et