16
P. K. Muduli et al.
Fig. 9 Mutual synchronization on the a first-, b second-, and c third-order Slonczewski modes for
a MTJ-STNO with two NCs having a nominal diameter of d NC = 150 nm and a center to center
spacing of 300 nm. Reprinted from Houshang et al. [79] Copyright (2018) by Nature Communications
separated 300 nm are shown in Fig. 9a–c. The behavior of the device as a function
of field at a constant drive current, is shown in Fig. 9a. At fields lower than 1.22
T, two distinct modes can be observed at high frequencies with a substantial noise
at low frequencies, indicative of a substantial interaction between the two modes.
By increasing the field, these two modes merge into one and at the same time, the
low-frequency noise disappears which is consistent with mutual synchronization. A
set of new devices with a thicker bottom electrode to sustain more current, were
used to study the synchronization behaviour as a function of drive current. As can
be seen in Fig. 9b, at 1.18 T, two fist order Slonczewski modes can be detected
at currents I dc < −13 mA. Increasing the amount of drive current, first one of the
NCs jump to second-order at about I dc = −13 mA and then the second NC at about
I dc = −17 mA after which the two modes merge and synchronize at about −18 mA.
Increasing the applied field to 1.45 T, the second order modes do not synchronize
at all while the third-order modes are synchronized. Therefore, it is possible to tune
the applied field and drive current so that synchronization is achieved for each of the
three Slonczewski modes.
Being able to generate high-order Slonczewski modes means that one can generate
modes with much shorter wavelengths, in this 120 nm and 74 nm for the secondand third-order modes. Having access to larger wavevectors also indicates that the
group velocity of these waves are also higher since the group velocity increases
with wavevector v gr 4γ A ex k/M s . This means not only SWs can travel much faster
but much further before they get damped out which has significant implications for
practical applications of magnonic devices.
P. K. Muduli et al.
Fig. 9 Mutual synchronization on the a first-, b second-, and c third-order Slonczewski modes for
a MTJ-STNO with two NCs having a nominal diameter of d NC = 150 nm and a center to center
spacing of 300 nm. Reprinted from Houshang et al. [79] Copyright (2018) by Nature Communications
separated 300 nm are shown in Fig. 9a–c. The behavior of the device as a function
of field at a constant drive current, is shown in Fig. 9a. At fields lower than 1.22
T, two distinct modes can be observed at high frequencies with a substantial noise
at low frequencies, indicative of a substantial interaction between the two modes.
By increasing the field, these two modes merge into one and at the same time, the
low-frequency noise disappears which is consistent with mutual synchronization. A
set of new devices with a thicker bottom electrode to sustain more current, were
used to study the synchronization behaviour as a function of drive current. As can
be seen in Fig. 9b, at 1.18 T, two fist order Slonczewski modes can be detected
at currents I dc < −13 mA. Increasing the amount of drive current, first one of the
NCs jump to second-order at about I dc = −13 mA and then the second NC at about
I dc = −17 mA after which the two modes merge and synchronize at about −18 mA.
Increasing the applied field to 1.45 T, the second order modes do not synchronize
at all while the third-order modes are synchronized. Therefore, it is possible to tune
the applied field and drive current so that synchronization is achieved for each of the
three Slonczewski modes.
Being able to generate high-order Slonczewski modes means that one can generate
modes with much shorter wavelengths, in this 120 nm and 74 nm for the secondand third-order modes. Having access to larger wavevectors also indicates that the
group velocity of these waves are also higher since the group velocity increases
with wavevector v gr 4γ A ex k/M s . This means not only SWs can travel much faster
but much further before they get damped out which has significant implications for
practical applications of magnonic devices.