Homodyne-detected ferromagnetic resonance of in-plane magnetized nanocontacts: Composite spin-wave resonances and their excitation mechanism

Abstract

This work provides a detailed investigation of the measured in-plane field-swept homodynedetected ferromagnetic resonance (FMR) spectra of an extended Co/Cu/NiFe pseudo spin valve stack using a nanocontact (NC) geometry. The magnetodynamics are generated by a pulsemodulated microwave current and the resulting rectified dc mixing voltage, which appears across the NC at resonance, is detected using a lock-in amplifier. Most notably, we find that the measured spectra of the NiFe layer are composite in nature and highly asymmetric, consistent with the broadband excitation of multiple modes. Additionally, the data must be fit with two Lorentzian functions in order to extract a reasonable value for the Gilbert damping of the NiFe. Aided by micromagnetic simulations, we conclude that (i) for in-plane fields the rf Oersted field in the vicinity of the NC plays the dominant role in generating the observed spectra, (ii) in addition to the FMR mode, exchange dominated spin waves are also generated, and (iii) the NC diameter sets the mean wavevector of the exchange dominated spin wave, in good agreement with the dispersion relation.

Fast micromagnetic simulations on GPU—recent advances made with $\mathsf{mumax}^3$

“…It is worth mentioning that those were the very first simulations that stud ied ultrafast and picosecond magnetization dynamics simulta neously in largescale magnetic structures. Recently, micromagnetic modeling was also employed to reveal the origin of the asymmetric lineshape in socalled all metallic pseudo spin valves driven by RF currents injected through the nanocontact [198]. It was demonstrated that, in contrast to the direct current driven case, the microwave Oersted field generated by the nanocontact provides a broad band excitation of the propagating exchangedominated spin waves.…”

Equations of motion and frequency dependence of magnon-induced domain wall motion

“…[6][7][8][9][10][11][12][13] However, the dynamics of the collective coordinates also depends strongly on the spin-wave amplitude ρ. Since the spin-wave amplitude depends on the frequency of the applied excitation field [25][26][27][28] it is the spatial profile of the applied excitation field that plays the main role in determining the frequency dependence of the domain wall velocity in some of these studies.…”

“…The spatial profile of the microwave source determines how the spin-wave amplitude depends on the driving frequency. [25][26][27][28] We derive a special case of Kalinikos' general formula 25 and show that the spin-wave amplitude is proportional to the Fourier sine transform of the source profile. We then use the dependence of the spin-wave amplitude on the microwave frequency to find consistent results for how the domain wall velocity depends on the driving frequency in the numerical and analytical calculations.…”

Reduced spin torque nano-oscillator linewidth using He+ irradiation

“…To accurately determine M eff of the [Co/Ni] free layer, spin-torque ferromagnetic resonance (ST-FMR) [36][37][38][39][40] measurements were performed on the He + -irradiated STNOs (see details in supplemental materials [41]). The fluence information and the obtained effective magnetization µ 0 M eff are presented in Table I.…”