Magnetic nutation: transient separation of magnetization from its angular momentum

Abstract

For nearly 90 years, precession and relaxation processes have been thought to dominate magnetization dynamics. Only recently has it been considered that, on short time scales, an inertia-driven magnetization dynamics should become relevant, leading to additional nutation of the magnetization vector. Here, we trigger magnetic nutation via a sudden excitation of a thin Ni80Fe20 (Permalloy) film with an ultrashort optical pulse, that leads to an abrupt tilting of the effective field acting on the magnetic moments, separating the dynamics of the magnetization from that of its angular momentum. We investigate the resulting magnetization dynamics in the inertial regime experimentally by the time-resolved magneto optical Kerr effect. We find a characteristic oscillation in the Kerr signal in the range of about 0.1 THz superimposed on the precessional oscillations with GHz frequencies. By comparison with atomistic spin dynamics simulations, we demonstrate that this observation cannot be explained by the well-known Landau-Lifshitz-Gilbert equation of motion but can be attributed to inertial contributions leading to nutation of the magnetization vector around its angular momentum. Hence, an optical and non-resonant excitation of inertial magnetization dynamics can trigger and control different magnetic processes, ranging from demagnetization via nutation to precession in a single device. These findings will have profound implications for the understanding of ultrafast spin dynamics and magnetization switching.

References in corpus (20)

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• Coherent and incoherent magnons induced by strong ultrafast demagnetization in thin permalloy films

Cited by in corpus (6)

• Nonreciprocal inertial spin-wave dynamics in twisted magnetic nanostrips
• Engineering spin-wave spectrum via the magnetization inertia tensor
• Unquenched orbital angular momentum as the origin of spin inertia
• Field-derivative torque induced magnetization reversal in ferrimagnetic Gd${}_{3/2}$Yb${}_{1/2}$BiFe${}_5$O${}_{12}$
• Chirality and polarization of inertial antiferromagnetic resonances driven by spin-orbit torques
• Optically induced magnetic inertia and magnons from non-Markovian extension of the Landau-Lifshitz-Gilbert equation