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In this work, we investigate the use of post-fabrication thermal nanoconversion (TNC), using a heated scanning probe tip, to modify the magnetic properties of Ni80Fe20 elliptical nanoislands with varying aspect ratio. Despite Ni80Fe20 being unoptimized for TNC, by comparing quasistatic and dynamic magneto-optical Kerr effect microscopy measurements, we demonstrate that TNC at a contact temperature of 250 °C increases the saturation magnetization of the treated nanoislands, reaching a value close to 800 kA/m. Micromagnetic simulations of the nanoislands indicate that the TNC technique can be used to alter the remanent state, from a single domain to a vortex. These results demonstrate the opportunities afforded by TNC to modify the properties of selected areas in a thin film or a patterned sample, particularly when designing magnonic crystals and other nanomagnetic devices. [ABSTRACT FROM AUTHOR]

Picosecond magnetization dynamics in the free and pinned layers of a microscale magnetic tunnel valve have been studied using time-resolved scanning Kerr microscopy. A comparison of the observed dynamics with those of individual free and pinned layers allowed the effect of interlayer coupling to be identified. A weak interlayer coupling in the tunnel valve continuous film reference sample was detected in bulk magnetometry measurements, while focused Kerr magnetometry showed that the coupling was well maintained in the patterned structure. In the tunnel valve, the free layer precession was observed to have reduced amplitude and an enhanced relaxation. During magnetization reversal in the pinned layer, its frequency approached that of the low frequency mode associated with the free layer. At the pinned layer switching field, the linewidth of the free layer became similar to that of the pinned layer. The similarity in their frequencies promotes the formation of precessional modes that exhibit strong collective properties such as frequency shifting and enhanced linewidth, while inhomogeneous magnetization of the pinned layer during reversal may also play a role in these observations. The collective character of precessional dynamics associated with mixing of the free and pinned layer magnetization dynamics must be accounted for even in tunnel valves with a small interlayer coupling. [ABSTRACT FROM AUTHOR]

Dynamic dipolar interactions between spin wave eigenmodes of closely spaced nanomagnets determine the collective behavior of magnonic and spintronic metamaterials and devices. However, dynamic dipolar interactions are difficult to quantify since their effects must be disentangled from those of static dipolar interactions and variations in the shape, size, and magnetic properties of the nanomagnets. It is shown that when two imperfect nanoscale magnetic disks with similar but nonidentical modes are brought into close proximity, the effect of the dynamic dipolar interaction can be detected by considering the difference of the phase of precession within the two disks. Measurements show that the interaction is stronger than expected from micromagnetic simulations, highlighting both the need for characterization and control of magnetic properties at the deep nanoscale, and also the potential for improved control of collective magnetic phenomena. Our approach is equally applicable to other physical systems in which dynamic interactions are obscured by inhomogeneous broadening and static interactions. [ABSTRACT FROM AUTHOR]