3D Nanomagnetic Logic
277
Typical results of OOMMF thermal micromagnetic simulations are depicted in
Fig. 10b. The magnetization is recorded for each simulation result and each magnet
reversal is evaluated in terms of switching time. For high B z pulses (55 mT), the
switching immediately occurs during the rising z-field pulse. Medium B z pulses
(47 mT) have a broadly distributed switching time from the beginning of the z-pulse
up until the x-field is applied. For low B z pulses (41 mT), the in-plane field pulse is
most effective and the switching time can be as narrow as the in-plane pulse in xdirection. This means, that in-plane pulses can very effectively reduce the distribution
and can be used for synchronous switching of the ANC. Figure 10d is summarizing
the results for increasing B z -pulse amplitude (40 mT ≤ B z ≤ 59 mT) with narrowest
switching field distribution for 42 mT ≤ B z ≤ 45 mT. This is of great importance for
ANC operation: For memory applications, one could of course use pulses with highest
B z amplitude, as only highest switching probability is needed. However, for logic
applications in field-coupled devices, the range of medium or low B z amplitudes are
of great importance, as in those ranges field coupling can be applied most effectively.
Please note, the absolute values discussed do not present a general physical rule
but rather a specific technology that was calibrated with a certain type of Co/Pt
bilayer stack. It demonstrated the effectiveness of in-plane pulses for ANC reversal
with spatially varying perpendicular anisotropy as experimentally demonstrated in
[50]. The vector nature of the applied field-pulses are of vital importance for device
optimization, as neither the local coupling-fields nor the externally applied Zeemanfields can be reduced to simple out-of-plane fields. Instead the switching amplitudes
can be influenced by in-plane fields and there is research on-the-way which refines
the ANC switching models by a combination of in-plane and out-of-plane pulses with
good control over pulse-timing. To summarize the state-of-the-art in ANC modeling,
the following procedure turned out to be practicable:
1. Measure film anisotropy with common methods like the Extraordinary Hall-effect
and rotating magnetic field [51]. This gives an upper limit for the anisotropy of a
scaled NML device.
2. Fabricate small islands and create an ANC, measure the switching field on small
time-scales for field-pulses, possibly in in-plane and and out-of-plane-direction.
3. Match the switching field by adopting A exch and K u -profile in the ANC and
simulate at the same time-scales. ANC dimensions are estimated from the software
collection Stopping and Range of Ions in Matter (SRIM) simulations or SEMimages.
4. Thermal OOMMF-simulations [36] with a Langevin term provide distributions
and comparison to the experiment on the nanosecond time-scale.
5. Compare both experiment and micromagnetic simulation.
6. Parameterize possible analytical descriptions of the nucleation and reversal
process.
277
Typical results of OOMMF thermal micromagnetic simulations are depicted in
Fig. 10b. The magnetization is recorded for each simulation result and each magnet
reversal is evaluated in terms of switching time. For high B z pulses (55 mT), the
switching immediately occurs during the rising z-field pulse. Medium B z pulses
(47 mT) have a broadly distributed switching time from the beginning of the z-pulse
up until the x-field is applied. For low B z pulses (41 mT), the in-plane field pulse is
most effective and the switching time can be as narrow as the in-plane pulse in xdirection. This means, that in-plane pulses can very effectively reduce the distribution
and can be used for synchronous switching of the ANC. Figure 10d is summarizing
the results for increasing B z -pulse amplitude (40 mT ≤ B z ≤ 59 mT) with narrowest
switching field distribution for 42 mT ≤ B z ≤ 45 mT. This is of great importance for
ANC operation: For memory applications, one could of course use pulses with highest
B z amplitude, as only highest switching probability is needed. However, for logic
applications in field-coupled devices, the range of medium or low B z amplitudes are
of great importance, as in those ranges field coupling can be applied most effectively.
Please note, the absolute values discussed do not present a general physical rule
but rather a specific technology that was calibrated with a certain type of Co/Pt
bilayer stack. It demonstrated the effectiveness of in-plane pulses for ANC reversal
with spatially varying perpendicular anisotropy as experimentally demonstrated in
[50]. The vector nature of the applied field-pulses are of vital importance for device
optimization, as neither the local coupling-fields nor the externally applied Zeemanfields can be reduced to simple out-of-plane fields. Instead the switching amplitudes
can be influenced by in-plane fields and there is research on-the-way which refines
the ANC switching models by a combination of in-plane and out-of-plane pulses with
good control over pulse-timing. To summarize the state-of-the-art in ANC modeling,
the following procedure turned out to be practicable:
1. Measure film anisotropy with common methods like the Extraordinary Hall-effect
and rotating magnetic field [51]. This gives an upper limit for the anisotropy of a
scaled NML device.
2. Fabricate small islands and create an ANC, measure the switching field on small
time-scales for field-pulses, possibly in in-plane and and out-of-plane-direction.
3. Match the switching field by adopting A exch and K u -profile in the ANC and
simulate at the same time-scales. ANC dimensions are estimated from the software
collection Stopping and Range of Ions in Matter (SRIM) simulations or SEMimages.
4. Thermal OOMMF-simulations [36] with a Langevin term provide distributions
and comparison to the experiment on the nanosecond time-scale.
5. Compare both experiment and micromagnetic simulation.
6. Parameterize possible analytical descriptions of the nucleation and reversal
process.