-The dynamical motion of the magnetization plays a key role in the properties of magnetic materials. If the magnetization is initially away from the equilibrium direction in a magnetic nanoparticle, it will precess at a natural frequency and, with some damping present, will decay to the equilibrium position in a short lifetime. Here we investigate a simple but important situation where a magnetic nanoparticle is driven non-resonantly by an oscillating magnetic field, not at the natural frequency. We find a surprising result that the lifetime of the transient motion is strongly tunable, by factors of over 10,000, by varying the amplitude of the driving field.Introduction. -A wide variety of fascinating topics have been studied in nonlinear magnetism [1][2][3] and other branches of nonlinear physics. These include solitons [4][5][6][7], period doubling [8], nonlinear combinations of frequencies [9, 10], strange attractors, limit cycles, chaos [11], and routes to chaos through bifurcation processes [12,13]. The field has recently been invigorated by the use of nanostructures, which have allowed very large microwave fields to be applied, with amplitudes in excess of several hundred Oe [14,15], and have allowed interesting nonlinear conversion between modes [16][17][18]. Almost all of these topics deal with what is happening in the system after all transients have disappeared [19,20].In this paper, in contrast, we theoretically examine the transient precessional behavior appropriate for a magnetic nanoparticle. We find a surprising result that, in the nonlinear limit, the transient lifetime can be significantly extended by adding a strong oscillating driving field which is at a different frequency than the natural frequency. This increase of the lifetime depends sensitively (and nonmontonically) on the strength of the driving field. Near a critical driving field the lifetime can be extended by factors of over 10,000. We note that this behavior occurs in a nonlinear regime, but chaos is not required for this stabilization of the transient.
