Magnetic droplet solitons in orthogonal spin valves
We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets...
Saved in:
| Published in: | Физика низких температур |
|---|---|
| Date: | 2015 |
| Main Authors: | , , , , , , , , |
| Format: | Article |
| Language: | English |
| Published: |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2015
|
| Subjects: | |
| Online Access: | https://nasplib.isofts.kiev.ua/handle/123456789/128089 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Journal Title: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Cite this: | Magnetic droplet solitons in orthogonal spin valves / S.Chung, S.M. Mohseni, A. Eklund, P. Dürrenfeld, M. Ranjbar, S.R. Sani, T.N.A. Nguyen, R.K. Dumas, J. Åkerman // Физика низких температур. — 2015. — Т. 41, № 10. — С. 1063–1068. — Бібліогр.: 62 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
nasplib_isofts_kiev_ua-123456789-128089 |
|---|---|
| record_format |
dspace |
| spelling |
Chung, S. Mohseni, S.M. Eklund, A. Dürrenfeld, P. Ranjbar, M. Sani, S.R. Nguyen, T.N.A. Dumas, R.K. Åkerman, J. 2018-01-05T17:58:57Z 2018-01-05T17:58:57Z 2015 Magnetic droplet solitons in orthogonal spin valves / S.Chung, S.M. Mohseni, A. Eklund, P. Dürrenfeld, M. Ranjbar, S.R. Sani, T.N.A. Nguyen, R.K. Dumas, J. Åkerman // Физика низких температур. — 2015. — Т. 41, № 10. — С. 1063–1068. — Бібліогр.: 62 назв. — англ. 0132-6414 PACS: 75.30.Ds, 75.75.–c https://nasplib.isofts.kiev.ua/handle/123456789/128089 We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented. en Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України Физика низких температур Специальный выпуск К 80-летию уравнения Ландау–Лифшица Magnetic droplet solitons in orthogonal spin valves Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Magnetic droplet solitons in orthogonal spin valves |
| spellingShingle |
Magnetic droplet solitons in orthogonal spin valves Chung, S. Mohseni, S.M. Eklund, A. Dürrenfeld, P. Ranjbar, M. Sani, S.R. Nguyen, T.N.A. Dumas, R.K. Åkerman, J. Специальный выпуск К 80-летию уравнения Ландау–Лифшица |
| title_short |
Magnetic droplet solitons in orthogonal spin valves |
| title_full |
Magnetic droplet solitons in orthogonal spin valves |
| title_fullStr |
Magnetic droplet solitons in orthogonal spin valves |
| title_full_unstemmed |
Magnetic droplet solitons in orthogonal spin valves |
| title_sort |
magnetic droplet solitons in orthogonal spin valves |
| author |
Chung, S. Mohseni, S.M. Eklund, A. Dürrenfeld, P. Ranjbar, M. Sani, S.R. Nguyen, T.N.A. Dumas, R.K. Åkerman, J. |
| author_facet |
Chung, S. Mohseni, S.M. Eklund, A. Dürrenfeld, P. Ranjbar, M. Sani, S.R. Nguyen, T.N.A. Dumas, R.K. Åkerman, J. |
| topic |
Специальный выпуск К 80-летию уравнения Ландау–Лифшица |
| topic_facet |
Специальный выпуск К 80-летию уравнения Ландау–Лифшица |
| publishDate |
2015 |
| language |
English |
| container_title |
Физика низких температур |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| format |
Article |
| description |
We review the recent experimental advancements in the realization and understanding of magnetic droplet
solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs)
fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using
the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet
nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation
changes gradually from a single sharp step well above this field, mode-hopping around the minimum,
and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability
and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue
that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current
minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally,
evidence of an edge mode droplet in a nanowire is presented.
|
| issn |
0132-6414 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/128089 |
| citation_txt |
Magnetic droplet solitons in orthogonal spin valves / S.Chung, S.M. Mohseni, A. Eklund, P. Dürrenfeld, M. Ranjbar, S.R. Sani, T.N.A. Nguyen, R.K. Dumas, J. Åkerman // Физика низких температур. — 2015. — Т. 41, № 10. — С. 1063–1068. — Бібліогр.: 62 назв. — англ. |
| work_keys_str_mv |
AT chungs magneticdropletsolitonsinorthogonalspinvalves AT mohsenism magneticdropletsolitonsinorthogonalspinvalves AT eklunda magneticdropletsolitonsinorthogonalspinvalves AT durrenfeldp magneticdropletsolitonsinorthogonalspinvalves AT ranjbarm magneticdropletsolitonsinorthogonalspinvalves AT sanisr magneticdropletsolitonsinorthogonalspinvalves AT nguyentna magneticdropletsolitonsinorthogonalspinvalves AT dumasrk magneticdropletsolitonsinorthogonalspinvalves AT akermanj magneticdropletsolitonsinorthogonalspinvalves |
| first_indexed |
2025-11-26T16:35:07Z |
| last_indexed |
2025-11-26T16:35:07Z |
| _version_ |
1850628248123211776 |
| fulltext |
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 10, pp. 1063–1068
Magnetic droplet solitons in orthogonal spin valves
Sunjae Chung1,2, S. Majid Mohseni3, Anders Eklund4, Philipp Dürrenfeld1, Mojtaba Ranjbar1,
Sohrab R. Sani2, T. N. Anh Nguyen2,5, Randy K. Dumas1, and Johan Åkerman1,2
1Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden
2Department of Materials and Nanophysics, School of Information and Communication Technology, KTH Royal In-
stitute of Technology, Electrum 229, 164 40 Kista, Sweden
3Department of Physics, Shahid Beheshti University, Tehran 19839, Iran
4Department of Integrated Devices and Circuits, School of Information and Communication Technology,
KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden
5Lab of Magnetism and Superconductivity, Institute of Materials Science, Vietnam Academy of Science and Tech-
nology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam
E-mail: johan.akerman@physics.gu.se
Received July 30, 2015, published online August 25, 2015
We review the recent experimental advancements in the realization and understanding of magnetic droplet
solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs)
fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied us-
ing the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet
nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nu-
cleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum,
and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instabil-
ity and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue
that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation cur-
rent minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally,
evidence of an edge mode droplet in a nanowire is presented.
PACS: 75.30.Ds Spin waves;
75.75.–c Magnetic properties of nanostructures.
Keywords: magnetic droplet soliton, spin torque, perpendicular anisotropy, magnetoresistance.
1. Introduction
The phenomenon of spin transfer torque (STT) [1–3], in
which angular momentum can be transferred from a spin
polarized current to a magnetic layer, has dramatically im-
pacted how magnetodynamics can be excited in magnetic
nanostructures. As STT can act as negative spin wave
damping, it can realize magnetic systems where spin waves,
instead of being damped out, can grow exponentially in
amplitude, until additional non-linear damping balances
the magnetodynamics and a steady state of intense spin
wave generation is realized [4–6]. This auto-oscillatory
state is the basis for spin torque nanooscillators (STNOs)
with promise for use as ultra-broadband, rapidly modulat-
ed, truly nanoscopic, and RF CMOS compatible micro-
wave signal generators [5–17].
While STNOs can be successfully fabricated in the form
of 100 nm diameter nanopillars of either spin valve [18] or
magnetic tunnel junction [19] stacks, nanocontact based
STNOs [20,21], in which the active magnetic layers are
laterally extended over several micrometers and only the
nanocontact is nanoscopic, typically offer much richer
magnetodynamics, entirely novel magnetodynamic modes,
and even magnetic solitons [22–25]. For example, in easy-
plane material based devices such as STNOs with Permal-
loy free layers, in addition to vortices [26–28], both propa-
© Sunjae Chung, S. Majid Mohseni, Anders Eklund, Philipp Dürrenfeld, Mojtaba Ranjbar, Sohrab R. Sani, T.N. Anh Ngu-
yen, Randy K. Dumas, and Johan Åkerman, 2015
Sunjae Chung et al.
gating spin waves [29–36] and self-localized spin wave
bullet solitons [31–33,37] can be generated experimentally.
Very recently, orthogonal spin valve STNOs with free
layers having perpendicular magnetic anisotropy were real-
ized [38,39]. While originally developed to achieve zero-
field operation, these STNOs were later shown to be able
to nucleate and sustain so-called magnetic droplet solitons
[40–44], which are the dissipative analog of the magnon
drop solitons suggested in the 1970s [22,24]. While the
magnetic droplet is of great fundamental interest in itself, it
also promises significant advantages in both microwave
and memory applications. As the magnetic droplet typical-
ly exhibits a partially reversed core a large fraction of its
spins precess at a very large angle and make use of much
more of the available magnetoresistance than many other
modes. While typical STNO precession angles reach a maxi-
mum of about 20 degrees [45], and hence generate only
about 10 % of the theoretical maximum microwave power,
droplets can ideally be made to precess close to 90 degrees
and consequently generate close to the maximum available
power. In memory applications, it has also been shown that
droplets are the necessary precursor to skyrmion injection
into skyrmion based race track memories [46].
In this paper we review the recent progress in realizing
magnetic droplets in different geometries and provide a
better understanding of some of their fundamental proper-
ties such as their nucleation and collapse boundaries. We
show magnetic droplet nucleation versus applied magnetic
field and electrical drive current. Furthermore, we argue
that the use of tilted anisotropy materials for the fixed layer
could greatly reduce the current and magnetic field re-
quired for magnetic droplet nucleation. Finally, the time
dependent resistance measurements of droplet collapse and
re-nucleation at high field strengths will be presented and
discussed as well as droplet nucleation in nanowires, as
required for future racetrack memories.
2. Experimental
The orthogonal spin valve stacks, Fig. 1(a), based
on Ta(4 nm)/Cu(10 nm)/Ta(4 nm)/Co(6 nm)/Cu(6 nm)/
Co(0.2 nm)–[Ni(0.6 nm)/Co(0.25 nm)]×4 were magne-
tron sputtered at room temperature on thermally oxidized
Si substrates in a chamber with a base pressure better than
5·10–8 Torr. The sputtering growth rates used for the ultra-
thin Co and Ni layers were less than 0.2–0.3 Å/s to maxim-
ize uniformity and minimize inter-diffusion. Using alternat-
ing gradient magnetometry we estimated the in-plane satura-
tion field 0 ( )k SH Mµ − of the free layer to be 0.35 T.
The subsequent fabrication of the STNOs includes the
following steps: (i) patterning the blanket films to either
a 8×16 µm2 mesa using optical lithography or 200 nm wide
nanowires using e-beam lithography, (ii) deposition of an in-
sulating SiO2 layer by chemical vapor deposition, (iii) de-
fining the NC area using electron-beam lithography, (iv) re-
active ion etching through the SiO2 to define the NC,
(v) deposition of a top contact electrode of Cu (1.1 µm)/Au
(100 nm), and (vi) forming the electrodes into a co-planar
waveguide using optical lithography and lift-off.
A custom probe station was used for magnetoelectrical
characterization of the STNOs utilizing applied fields per-
pendicular to the film stack. The generated microwave
signal was amplified using a broadband microwave ampli-
fier and measured in the frequency domain with a spectrum
analyzer. The dc voltage was simultaneously measured
across the device for magnetoresistance (MR) measure-
ments.
Time dependent STNO resistance measurements were
carried out via the 0–30 kHz dc port of the bias-T using
a EG&G 5113 low-noise amplifier utilizing ac coupling,
30 dB voltage gain and a 0–10 kHz bandwidth.
3. Results and discussions
3.1. Magnetic droplet nucleation current vs field
We will first discuss the results related to magnetic
droplets in extended films. Figures 1(a) and 1(b) show typ-
ical microwave and magnetoresistance measurements of
magnetic droplet nucleation as a function of applied field
Fig. 1. (Color online) The inset in (a) shows a schematic geome-
try of the orthogonal spin valve stack and a nanocontact (NC).
A transition from an ordinary high frequency mode to a magnetic
droplet is evident as a dramatic drop in frequency (a) and increase
in magnetoresistance (b), (red curve) as the applied field is in-
creased. As a reference in (b), (black curve) the magnetore-
sistance only shows a monotonic decrease for currents less than
the necessary nucleation current. (c)–(e) Snapshots from micro-
magnetic simulations showing the spin configurations of a (c)
conventional magnetic droplet nucleated in an extended free lay-
er, (d) an edge-mode magnetic droplet nucleated in a nanowire,
and (e) a quasi-1D droplet consisting of two precessing domain
walls which exhibit a well-defined breathing.
(a)
10
0
5
(c)
(b)
(d)
(e)
30
25
20
15
10
0.2
0.2 0.4 0.6 0.8 1.0
–0.4
–0.6
–0.8
–1.0
ST
O
fr
eq
ue
nc
y,
G
H
z
Magnetic field, T
M
ag
ne
to
re
si
st
an
ce
,
%
– 4.8 mA
– 5.3 mA
1064 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 10
Magnetic droplet solitons in orthogonal spin valves
at a fixed current. These extended layers support the tradi-
tional magnetic droplet soliton, depicted schematically in
Fig. 1(c), where the core is partially reversed and the spins
both in the core and in the droplet perimeter precess in-
phase. Although droplet theory [40] was developed for fully
perpendicular spin valves, reported experiments [41,44]
have used STNOs where the remanent state of the fixed
layer is in the film plane, which can promote droplet insta-
bility and auto-modulation [41,47–49]. In this orthogonal
geometry, the current–field phase diagram of the droplet
qualitatively differs from the theoretical predictions. Alt-
hough experiments and theory agree at high fields where
the fixed layer is saturated out-of-plane [44], the low-field
behavior of the droplet nucleation current instead scales
well with the perpendicular component of the spin polari-
zation [41]. At intermediate fields both these descriptions
appear to break down [42].
To investigate these different behaviors in detail, we
study droplet nucleation over a wider field range in a STNO
with a 90 nm diameter NC. Figure 2 shows the STNO re-
sistance vs current for fields ranging from 1.1 to 1.8 T,
where the formation of the droplet can be monitored as a
step-like increase in the resistance, as indicated with trian-
gle symbols. There is a clear minimum in the nucleation
current at intermediate fields, which connects the two dif-
ferent dependencies observed in Refs. 41 and 44. We as-
cribe the high field linear behavior to the usual linear field
dependence of reaching the Slonczewski spin wave insta-
bility in spin torque devices [29,50]. The low-field regime,
where the nucleation current has been found to be inverse-
ly proportional to the applied field [41, 42] is instead a
consequence of the gradual out-of-plane tilting of the fixed
layer. The primary limiting factor to reach the Slonczewski
spin wave instability in this regime is the amount of per-
pendicular spin polarization in the STNO current.
Finding the minimum nucleation current is important
for applications as one typically would like to reduce the
power consumption. The decreasing perpendicular spin
polarization at low fields is therefore undesirable. It would
be advantageous if one could use both a low field and a
low current and still be able to nucleate a magnetic droplet.
While a fully perpendicular STNO, such as that assumed in
the original prediction of droplets [40], would have the
lowest nucleation current, it would on the other hand also
not have any output signal, since the symmetry of the
magnetodynamics would not generate a time-varying
STNO resistance. Instead we argue that a fixed layer based
on tilted anisotropy materials [51–60] would be ideal for
droplet nucleation and operation. In Fig. 3 we schematical-
ly compare the present STNOs with a STNO based on a
tilted anisotropy fixed layer. Since the magnetization angle
at the top of the tilted exchange spring can be tuned by
tailoring the individual thicknesses of the perpendicular
and easy-plane layers respectively, it will be possible to
optimize this system for both zero-field operation and
droplet nucleation at a minimal current. We consequently
expect significant a research effort in this direction to be
carried out soon.
Fig. 2. (Color online) Resistance vs applied current at different
external out-of-plane fields between 1.1 and 1.8 T. Plots are ver-
tically shifted for clarity. The droplet nucleation current is depict-
ed with a triangle in each measurement.
Fig. 3. (Color online) The left schematic shows the original or-
thogonal stack in which magnetic droplets were first discovered.
In the right schematic, the fixed layer has been replaced with a
tilted exchange spring, e.g. [Co/Pd]-NiFe, in which the remanent
out-of-plane angle of the NiFe spins can be freely tailored. As
described in the text, this is expected to remove any need for an
applied field to observe droplets.
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 10 1065
Sunjae Chung et al.
3.2. Magnetic droplet collapse and re-nucleation
It can be seen in Fig. 2 that the droplet nucleation as a
function of current is step-wise at high fields, more gradual
at the lowest fields, and shows a mode-hopping behavior at
intermediate fields. The mechanism responsible for this
phenomenon is most likely the drift instability predicted in
the original numerical droplet demonstration [40]. At the
high field end of Fig. 2 the droplet appears entirely stable
and a single well-defined nucleation event triggers the re-
sistance step. At intermediate fields, where the tilt angle of
the fixed layer is smaller, the drift instability becomes ac-
tive but is still relatively rare, such that a small number of
drift instability events occur during the initial current ramp.
However, as the current is well above the nucleation
threshold, a new droplet immediately re-nucleates and this
appears like discrete mode-hopping. Finally, at the lowest
fields, there is neither a sharp step nor any signs of mode-
hopping. Instead there is a smooth gradual resistance
change. We interpret this as the mean time between drift
instability events being much shorter than the integration
time of the resistance measurement. As the STNO is again
above the nucleation threshold, every drift instability event
is immediately followed by a droplet re-nucleation and the
resistance measurement now reflects the ratio between the
STNO being in a droplet state or in a uniform state. This
ratio manifests itself as a smooth function of current.
We have previously shown that droplet collapse at high
fields can exhibit similar signs of mode hopping [43]. In
Fig. 4 we present time-dependent resistance measurements
of a different STNO at high perpendicular field using
a real-time sampling oscilloscope to record long time-
traces at high temporal resolution. At the operating cur-
rent of –6.4 mA the collapse field as measured by ordinary
resistance and microwave signal generation is about 1.77 T.
However, when the same device is measured using the
oscilloscope, one can clearly observe sharp transitions be-
tween a high and a low resistance state. At 1.75 T, the
dominating state is the droplet, whereas at 1.79 T, the uni-
form state has almost entirely replaced it. At 1.77 T the
times spent in the droplet and uniform state, respectively,
are more equal.
3.3. Magnetic droplets in nanowires
We finally turn to droplets in reduced dimensions. Ac-
cording to previous micromagnetic simulations [61] the
droplet in an extended free layer, Fig. 1(c), undergoes a
transition to an edge droplet mode, Fig. 1(d), when the
nanowire has a width between 2–3.5 times the NC diame-
ter. This edge droplet mode is a consequence of the attrac-
tion from the nanowire boundary [62]. Additionally, the
edge droplet has a much larger mode volume, which is
governed by the nanowire width rather than the NC size,
yielding an effectively lower oscillation frequency [40].
For nanowire widths smaller than twice the NC diameter,
the micromagnetic simulations showed the existence of
a quasi one-dimensional droplet mode, Fig. 1(e), where
the expansion of the dynamics across the nanowire width
results in a breathing pair of domain walls with sub-
Zeeman oscillation frequencies.
A scanning electron micrograph of a 200 nm wide nan-
owire spin valve structure with a NC diameter of 70 nm is
shown in the upper inset of Fig. 5. The STNO frequency
spectra as a function of the applied perpendicular field is
shown in the main panel of Fig. 5. The frequency is below
the FMR frequency for all conditions, consistent with the
formation of a droplet. However, at a field of 0.7 T, a sharp
decrease of the oscillation frequency by 1 GHz is ob-
served. A similar drop in frequency is also present in a
current sweep at the constant field of 0.75 T, as shown in
the lower inset of Fig. 5. We believe that this drop in fre-
quency is consistent with the formation of the edge mode,
where the droplet extends in an arc from the NC to the
nanowire edge. These first experimental results demon-
Fig. 4. (Color online) Time dependent STNO resistance meas-
urements at I = = –6.4 mA in three slightly different perpendicu-
lar fields, T of 1.75 T (a), 1.77 (b) and 1.79 (c). The high-
resistance state indicates the presence of a magnetic droplet,
whereas the low-resistance state indicates a uniform, non-droplet,
magnetic state. The over- and undershooting spikes stem from the
amplifier low-pass filter.
1066 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 10
Magnetic droplet solitons in orthogonal spin valves
strating the nucleation of droplets in nanowires are espe-
cially promising for the implementation of confined mag-
netic solitons into nanostructured devices, e.g. racetrack
memories.
4. Conclusions
In summary, we have presented a brief review of the
most recent experiments and advances related to magnetic
droplet solitons in orthogonal spin valves. In particular, we
provided a detailed investigation regarding droplet nuclea-
tion over a wide range of currents and fields. Not only did
we observe a clear minimum in the nucleation current, but
were also able to resolve important differences in exactly
how a droplet nucleates at different applied fields. For ex-
ample, at large applied fields droplet nucleation occurs by
a single well-defined event. However, for smaller fields
this transition begins to blur as the role of the drift instabil-
ity promotes more complex nucleation/re-nucleation dy-
namics, which is also evident in additional time-resolved
measurements. Our latest measurements on droplet nuclea-
tion in orthogonal spin valve nanowires provides the first
experimental evidence of fundamentally new droplet dy-
namics, namely a unique droplet edge-mode, where the
physical boundaries of the nanowire begin to play an im-
portant role on the overall magnetodynamics. Future pro-
spects include the use of tilted fixed layers, which will al-
low for further optimization of the dynamics and
potentially zero-field operation, and skyrmion nucleation
in nanowires for racetrack memories, both of which will be
useful for next generation spintronic and magnonic device
applications.
1. L. Berger, Phys. Rev. B 54, 9353 (1996).
2. J.C. Slonczewski, J. Magn. Magn. Mater. 159 L1 (1996).
3. D. Ralph and M. Stiles, J. Magn. Magn. Mater. 320, 1190
(2008).
4. A. Slavin and V. Tiberkevich, Magnetics, IEEE Trans-
actions 45, 1875 (2009).
5. J.V. Kim, Solid State Phys. 63, 217 (2012).
6. T. Silva and W. Rippard, J. Magn. Magn. Mater. 320, 1260
(2008).
7. M.R. Pufall, W.H. Rippard, S. Kaka, T.J. Silva, and S.E.
Russek, Appl. Phys. Lett. 86, 082506 (2005).
8. A. Eklund, S. Bonetti, S.R. Sani, S. Majid Mohseni, J. Persson,
S. Chung, S. Amir Hossein Banuazizi, E. Iacocca, M. Östling,
J. Åkerman, and B. Gunnar Malm, Appl. Phys. Lett. 104,
092405 (2014).
9. J. Persson, S.R. Sani, S. Bonetti, F. Magnusson, Y. Pogorylov,
S.M. Mohseni, S. Gunnarsson, M. Norling, C. Stoij, and J.
Åkerman, IEEE Trans. Magn. 48, 4378 (2012).
10. P.K. Muduli, Y. Pogoryelov, Y. Zhou, F. Mancoff, and J.
Åkerman, Integr. Ferroelectr. 125, 147 (2011).
11. P.K. Muduli, Y. Pogoryelov, S. Bonetti, G. Consolo, F.
Mancoff, and J. Åkerman, Phys. Rev. B 81, 140408(R)
(2010).
12. Y. Pogoryelov, P.K. Muduli, S. Bonetti, E. Iacocca,
F. Mancoff, and J. Åkerman, Appl. Phys. Lett. 98, 192501
(2011).
13. Y. Pogoryelov, P.K. Muduli, S. Bonetti, F. Mancoff, and
J. Åkerman, Appl. Phys. Lett. 98, 192506 (2011).
14. P.K. Muduli, O.G. Heinonen, and J. Åkerman, Phys. Rev. B
86, 174408 (2012).
15. P.K. Muduli, Y. Pogoryelov, F. Mancoff, and J. Åkerman,
IEEE Trans. Magn. 47, 1575 (2011).
16. Y. Pogoryelov, P.K. Muduli, and J. Åkerman, IEEE Trans.
Magn. 48, 4077 (2012).
17. T. Chen, A. Eklund, S. Sani, S. Rodrigueza, G. Malm,
J. Åkerman, and A. Rusu, Solid State Electronics 111, 91
(2015).
18. V.S. Pribiag, I.N. Krivorotov, G.D. Fuchs, P.M. Braganca,
O. Ozatay, J.C. Sankey, D.C. Ralph, and R.A. Buhrman,
Nat. Phys. 3, 498 (2007).
19. I.N. Krivorotov, N.C. Emley, J.C. Sankey, S.I. Kiselev, D.C.
Ralph, and R.A. Buhrman, Science 307, 228 (2005).
20. W. Rippard, M. Pufall, S. Kaka, S. Russek, and T. Silva,
Phys. Rev. Lett. 92, 027201 (2004).
21. R. Dumas, S. Sani, S. Mohseni, E. Iacocca, Y. Pogoryelov,
P. Muduli, S. Chung, P. Dürrenfeld, and J. Åkerman,
Magnet., IEEE Transact. 50, 1 (2014).
22. B. Ivanov and A. Kosevich, Zh. Eksp. Teor. Fiz. 72, 2000
(1977).
23. A. Kovalev, A. Kosevich, and K. Maslov, JETP Lett. 30, 296
(1979).
24. A. Kosevich, B. Ivanov, and A. Kovalev, Phys. Rep. 194,
117 (1990).
25. H.-B. Braun, Adv. Phys. 61, 1 (2012).
26. T. Devolder, A. Meftah, K. Ito, J.A. Katine. P. Crozat, and
C. Chappert, J. Appl. Phys. 101, 063916 (2007).
Fig. 5. (Color online) Power spectral density vs perpendicular
field at a constant current of –12 mA for a nanowire based
STNO. The top inset shows a SEM image of the 200 nm wide
nanowire including the etched hole for the final NC. The bottom
inset shows the power spectral density vs current in a constant
perpendicular field of 0.75 T.
200 nm width
= –12 mAIDC
f,
G
H
z
25
20
15
10
5
0
25
23
21
f,
G
H
z
0 0.2 0.4 0.6 0.8 1.0
Field, T
100 nm
fZeeman
f Zee
man
f FM
R
4
2
dB–8 –10 –12 –14 –16
Current, mA
Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 10 1067
Sunjae Chung et al.
27. S.R. Sani, J. Persson, S.M. Mohseni, V. Fallahi, and
J. Åkerman, J. Appl. Phys. 109, 07C913 (2011).
28. S.R. Sani, P. Durrenfeld, S.M. Mohseni, S. Chung, and
J. Åkerman, IEEE Trans. Magn. 49, 4331 (2013).
29. M. Tsoi, A. Jansen, J. Bass, W. Chiang, V. Tsoi, and P. Wyder,
Nature 406, 46 (2000).
30. M. Madami, S. Bonetti, G. Consolo, S. Tacchi, G. Carlotti,
G. Gubbiotti, F.B. Mancoff, M.A. Yar, and J. Åkerman,
Nature Nanotech. 6, 635 (2011).
31. S. Bonetti, V. Tiberkevich, G. Consolo, G. Finocchio, P.
Muduli, F. Mancoff, A. Slavin, and J. Åkerman, Phys. Rev.
Lett. 105, 217204 (2010).
32. S. Bonetti, V. Puliafito, G. Consolo, V.S. Tiberkevich, A.N.
Slavin, and J. Åkerman, Phys. Rev. B 85, 174427 (2012).
33. R.K. Dumas, E. Iacocca, S. Bonetti, S.R. Sani, S.M. Mohseni,
A. Eklund, J. Persson, O. Heinonen, and J. Åkerman, Phys.
Rev. Lett. 110, 257202 (2013).
34. F.B. Mancoff, N.D. Rizzo, B.N. Engel, and S. Tehrani,
Nature 437, 393 (2005).
35. S. Kaka, M.R. Pufall, W.H. Rippard, T.J. Silva, S.E. Russek,
and J.A. Katine, Nature 437, 389 (2005).
36. S.R. Sani, J. Persson, S.M. Mohseni, Y. Pogoryelov, P.K.
Muduli, A. Eklund, G. Malm, M. Käll, A. Dmitriev, and
J. Åkerman, Nat. Commun. 4, 2731 (2013).
37. V.E. Demidov, S. Urazhdin, and S.O. Demokritov, Nature
Mater. 9, 984 (2010).
38. W.H. Rippard, A.M. Deac, M.R. Pufall, J.M. Shaw, M.W.
Keller, S. E. Russek, and C. Serpico, Phys. Rev. B 81,
014426 (2010).
39. S.M. Mohseni, S.R. Sani, J. Persson, T.N. Anh Nguyen, S.
Chung, Y. Pogoryelov, and J. Åkerman, Phys. Status Solidi
Rapid Res. Lett. 5, 432 (2011).
40. M.A. Hoefer, T.J. Silva, and M.W. Keller, Phys. Rev. B 82,
054432 (2010).
41. S.M. Mohseni, S.R. Sani, J. Persson, T.N. Anh Nguyen, S.
Chung, Y. Pogoryelov, P.K. Muduli, E. Iacocca, A. Eklund,
R.K. Dumas, S. Bonetti, A. Deac, M.A. Hoefer, and J.
Åkerman, Science 339, 1295 (2013).
42. S.M. Mohseni, S.R. Sani, R. Dumas, J. Persson, T.N. Anh
Nguyen, S. Chung, Y. Pogoryelov, P. Muduli, E. Iacocca,
A. Eklund, and J. Åkerman, Physica B 435, 84 (2014).
43. S. Chung, S.M. Mohseni, S.R. Sani, E. Iacocca, R.K. Dumas,
T.N. Anh Nguyen, Y. Pogoryelov, P. K. Muduli, A. Eklund,
M. Hoefer, and J. Åkerman, J. Appl. Phys. 115, 172612
(2014).
44. F. Macià, D. Backes, and A.D. Kent, Nature Nanotech. 9,
992 (2014).
45. P.K. Muduli, O.G. Heinonen, and J. Åkerman, J. Appl. Phys.
110, 076102 (2011).
46. J. Sampaio, V. Cros, S. Rohart, A. Thiaville, and A. Fert,
Nature Nanotech. 8, 839 (2013).
47. R. Liu, W. Lim, and S. Urazhdin, Phys. Rev. Lett. 114,
137201 (2015).
48. G. Finocchio, V. Puliafito, S. Komineas, L. Torres, O. Ozatay,
T. Hauet, and B. Azzerboni, J. Appl. Phys. 114, 163908
(2013).
49. V. Puliafito, G. Siracusano, B. Azzerboni, and, G. Finocchio,
IEEE Magn. Lett. 5, 1 (2014).
50. J.C. Slonczewski, J. Magn. Magn. Mater. 195, 261 (1999).
51. Y. Zhou, S. Bonetti, C.L. Zha, and J. Åkerman, New J. Phys.
11, 103028 (2009).
52. Y. Zhou, C.L. Zha, S. Bonetti, J. Persson, and J. Åkerman,
Appl. Phys. Lett. 92, 262508 (2008).
53. C. Morrison, J.J. Miles, T.N. Anh Nguyen, Y. Fang, R.K.
Dumas, J. Åkerman, and T. Thomson, J. Appl. Phys. 117,
17B526 (2015).
54. T.N. Anh Nguyen, N. Benatmane, V. Fallahi, Y. Fang, S.M.
Mohseni, R.K. Dumas, and J. Åkerman, J. Magn. Magn.
Mater. 324, 3929 (2012).
55. L. Tryputen, F. Guo, F. Liu, T.N. Anh Nguyen, M.S.
Mohseni, S. Chung, Y. Fang, J. Åkerman, Phys. Rev. B 91, 1
(2015).
56. S. Chung, S.M. Mohseni, V. Fallahi, T.N. Anh Nguyen, N.
Benatmane, R.K. Dumas, and J. Åkerman, J. Phys. D. Appl.
Phys. 46, 125004 (2013).
57. T.N. Anh Nguyen, V. Fallahi, Q. Tuan Le, S. Chung, S.M.
Mohseni, R.K. Dumas, C.W. Miller, and J. Åkerman, Magn.,
IEEE Trans. 50, 2004906 (2014).
58. T.N. Anh Nguyen, R. Knut, V. Fallahi, S. Chung, Q.T. Le, S.
Mohseni, O. Karis, S. Peredkov, R. Dumas, C.W. Miller, and
J. Åkerman, Phys. Rev. Appl. 2, 044014 (2014).
59. S. Tacchi, T.N. Anh Nguyen, G. Carlotti, G. Gubbiotti, M.
Madami, R.K. Dumas, J.W. Lau, J. Åkerman, A. Rettori, and
M.G. Pini, Phys. Rev. B 87, 144426 (2013).
60. S. Tacchi, T.N. Anh Nguyen, G. Gubbiotti, M. Madami,
G. Carlotti, M.G. Pini, A. Rettori, V. Fallahi, R.K. Dumas,
and J. Åkerman, J. Phys. D. Appl. Phys. 47, 495004 (2014).
61. E. Iacocca, R.K. Dumas, L. Bookman, M. Mohseni, S. Chung,
M.A. Hoefer, and J. Åkerman, Phys. Rev. Lett. 112, 047201
(2014).
62. M.D. Maiden, L.D. Bookman, and M.A. Hoefer, Phys. Rev.
B 89, 180409 (2014).
1068 Low Temperature Physics/Fizika Nizkikh Temperatur, 2015, v. 41, No. 10
http://dx.doi.org/10.1063/1.4827384
1. Introduction
2. Experimental
3. Results and discussions
3.1. Magnetic droplet nucleation current vs field
3.2. Magnetic droplet collapse and re-nucleation
3.3. Magnetic droplets in nanowires
4. Conclusions
|