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Magnetic bit patterned media are intensely investigated for the realization of the areal recording density of greater than 1 terabit per square inch with the practical data processing speed in the magnetic recording system. As it becomes increasingly critical to tune the magnetization behavior for the recording media with the nanometer scale recording bits, it is of great importance to study the magnetization dynamics characterized by several important quantities such as the coercivity, precession frequency, Gilbert damping constant, and the switching field distribution, and their dependence on the geometrical and material parameters. Studies on the effect of shape, miniaturization, and material on these parameters are widely being conducted; however, very little research has been conducted on controlling the magnetization dynamics using the geometric structure of a patterned nanomagnet array.
In this work, we demonstrate a modification of the precession frequency of patterned ferromagnets in the presence of surface acoustic waves (SAW) through the magnetoelastic effect. We employ the time-resolved magnetooptic Kerr effect (TR-MOKE) to directly observe the picosecond magnetization dynamics in arrays of patterned nanomagnets. The pump laser pulses heat the periodically located metallic elements, locally stressing the surface and exciting SAWs in the substrate. It appears in the TR-MOKE signal as a strong nonmagnetic oscillation in addition to the characteristic magnetization precession. Carefully eliminating the contribution of the SAW in the TR-MOKE signal, we see a magnetization oscillation pinned at the frequency of the SAW in arrays of Co/Pd multilayers. This pinning is observed over a large range of externally applied field of more than 1000 Oe, modifying the precession frequency by the factor greater than two. The results demonstrate a significant modification of the magnetization dynamics by the magnetoelastic effect and its potential of adding an additional degree of freedom in the optimization of the characteristics of bit patterned media.