Observation of droplet soliton drift resonances in a spin-transfer-torque nanocontact to a ferromagnetic thin film

Effect of Temperature on Magnetic Solitons Induced by Spin-Transfer Torque

“…However, when varying the temperature, we also observe, in addition to the resistance fluctuations, a decrease in the overall resistance change with increasing temperature. We, thus, confirm that the increase in temperature reduces the effective amount of reversed magnetization either because the droplet state becomes smaller than the nanocontact or because on average it spends less time in the contact region, such as due to drift instabilities [21,25]. In Appendix C, the evaluation and the analysis of the overall change in the MR in different devices with the same layer stack is shown.…”

“…Representative high-frequency noise spectra versus dc current of our samples at room temperature are shown in Appendix A. A low-frequency signal with a characteristic time scale of hundreds of megahertz has been recently measured [21,23] in droplet states and has been associated with center-of-mass droplet motion, such as the droplet drifting outside the nanocontact region.…”

“…1(b), we plot a measured magnetoresistance curve [17,19,20] at a fixed current of 27 mA ramping the perpendicular applied field from high to low field at a fixed temperature of 150 K. This shows first the creation (at 1 T) and then the annihilation of the droplet state (0.4 T). Figure 1(c) shows a measured droplet stability map in magnetic field and current space [21,23] built from magnetoresistance curves measured at different applied current at a fixed temperature of 150 K. The no droplet state is plotted in gray and corresponds to a lower resistance state, whereas the green area represents the droplet state, a higher resistance state.…”

“…Dissipative magnetic droplet solitons (droplets hereafter) are nonlinear confined wave excitations consisting of partially reversed precessing spins that can be created in films with perpendicular magnetic anisotropy (PMA) through the local suppression of the magnetic damping [16]. Droplets have been experimentally created using the STT effect in nanocontacts to PMA films [17][18][19][20][21][22][23], and droplets are a particular case of STToscillators. Recently reported experiments have shown that the stability of these collective excitations is limited by the appearance of drift instabilities, which were attributed to the disorderlocal variations of the effective magnetic field [21,24].…”

“…Droplets have been experimentally created using the STT effect in nanocontacts to PMA films [17][18][19][20][21][22][23], and droplets are a particular case of STToscillators. Recently reported experiments have shown that the stability of these collective excitations is limited by the appearance of drift instabilities, which were attributed to the disorderlocal variations of the effective magnetic field [21,24]. Wills et al [25] identified theoretically an intrinsic deterministic linear instability and thermal fluctuations as additional instability mechanisms.…”