Magnetic vortices are characterized by the sense of in-plane magnetization circulation and by the polarity of the vortex core. With each having two possible states, there are four possible stable ...magnetization configurations that can be utilized for a multibit memory cell. Dynamic control of vortex core polarity has been demonstrated using both alternating and pulsed magnetic fields and currents. Here, we show controlled dynamic switching of spin circulation in vortices using nanosecond field pulses by imaging the process with full-field soft X-ray transmission microscopy. The dynamic reversal process is controlled by far-from-equilibrium gyrotropic precession of the vortex core, and the reversal is achieved at significantly reduced field amplitudes when compared with static switching. We further show that both the field pulse amplitude and duration required for efficient circulation reversal can be controlled by appropriate selection of the disk geometry.
We have characterized the magnetic reversal and thermal stability of bit-patterned media with a composite structure of Co (0.25 nm)/Pd (0.7 nm) 5 /Fe( X )/Pd (0.7 nm)/Co (0.25 nm) 5 , where X = 1, ...1.5 , and 2 nm. For 25 nm diameter islands separated by 35 nm, the average thermal stability of the islands is confirmed by analyzing the time-dependent coercive fields. However, by further analyzing the time-dependent hysteresis loop shape, we find a broad distribution of the effective energy barriers. We quantitatively show that this energy barrier distribution arises primarily from the dipolar interactions in these densely packed arrays and not from intrinsic distributions.
We demonstrate a simple method to tailor the magnetization reversal mechanisms of Co/Pt multilayers by depositing them onto large area nanoporous anodized alumina (AAO) with various aspect ratios, A ...= pore depth/diameter. Magnetization reversal of composite (Co/Pt)/AAO films with large A is governed by strong domain-wall pinning which gradually transforms into a rotation-dominated reversal for samples with smaller A, as investigated by a first-order reversal curve method in conjunction with analysis of the angular dependent switching fields. The change of the magnetization reversal mode is attributed to topographical changes induced by the aspect ratio of the AAO templates.
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