field-dependent XFMR fitting

Co-edge XFMR amplitude-vs-field and phase-vs-field data sets; MATLAB code for fitting (example: fit results shown in Fig. 4 in 10.1021/acs.nanolett.0c01868)<div><br></div><div>Abstract of the associated publication (10.1021/acs.nanolett.0c01868) - Spin currents can exert spin-transfer torques on magnetic systems even in the limit of vanishingly small net magnetization, as recently shown for antiferromagnets. Here, we experimentally show that a spin-transfer torque is operative in a macroscopic ensemble of weakly interacting, randomly magnetized Co nanomagnets. We employ element- and time-resolved X-ray ferromagnetic resonance (XFMR) spectroscopy to directly detect subnanosecond dynamics of the Co nanomagnets, excited into precession with cone angle ≳0.003° by an oscillating spin current. XFMR measurements reveal that as the net moment of the ensemble decreases, the strength of the spin-transfer torque increases relative to those of magnetic field torques. Our findings point to spin-transfer torque as an effective way to manipulate the state of nanomagnet ensembles at subnanosecond time scales.</div>