We are studying patterned nanomagnet arrays fabricated using the e-beam lithography tools available at NIST Boulder. We have already demonstrated the ability to fabricate arrays of 40 nm nanomagnets in a variety of materials. We have developed a novel magneto-optic microscope for measuring the dynamic response of individual nanomagnets at microwave frequencies. This particular tool, the heterodyne magneto-optic microwave microscope (H-MOMM), is especially sensitive to details of the ferromagnetic resonance spectrum. We are studying the homogeneity of the dynamic response in arrays of nanomagnets. We have already measured profound differences in static properties when different procedures are used for the fabrication of nanomagnet arrays. We are interested in pushing the H-MOMM technique to identify the spectra of defects in such nanostructures. For example, we have already extended H-MOMM into a quasi-spatially sensitive technique through the measurement of both “edge” modes (modes with large amplitude at the edge of a nanostructure) and “center” modes. Analysis of linewidth and the frequency response of these different modes provide information about the spatially varying spin environment within a nanostructure. Currently, such information cannot be resolved by any other technique. We also wish to use the H-MOMM to study the effects of pure spin currents in spintronic devices. Spin currents can be generated by an individual nanomagnet in contact with a conductive paramagnetic spin medium via the spin pumping effect: When a nanomagnet is pumped with a sufficiently strong microwave field, a dc spin current is created at the magnet/nonmagnet interface. This dc spin current in a nonmagnetic conductor can affect the magnetization dynamics of neighboring nanomagnets through a combination of diffusion and spin torque transfer effects. We are interested in studying the details of how the nanomagnet mode structure is affected by the presence of such pure dc spin currents.
Device fabrication; Ferromagnetic resonance; Magnetic nanostructures; Magneto-optic Kerr effect; Microwave measurements; Nanomagnets; Spintronics; Spin pumping;