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Vortex dynamics within arrays of square ferromagnetic nanoelements have been studied by time-resolved scanning Kerr microscopy (TRSKM), while x-ray photoemission electron microscopy has been used to investigate the equilibrium magnetic state of the arrays. An alternating field demagnetization process was found to initialize a distribution of equilibrium states within the individual elements of the array, including quasiuniform states and vortex states of different chirality and core polarization. Repeated initialization revealed some evidence of stochastic behavior during the formation of the equilibrium state. TRSKM with a spatial resolution of ~300 nm was used to detect vortex gyration within arrays of square nanoelements of 250-nm lateral size. Two arrays were studied consisting of a 9 × 9 and 5 × 5 arrangement of nanoelements with 50- and 500-nm element edge-to-edge separation to encourage strong and negligible dipolar interactions, respectively. In the 5 × 5 element array, TRSKM images, acquired at a fixed phase of the driving microwave magnetic field, revealed differences in the gyrotropic phase within individual elements. While some phase variation is attributed to the dispersion in the size and shape of elements, the vortex chirality and core polarization are also shown to influence the phase. In the 9 × 9 array, strong magneto-optical response due to vortex gyration was observed across regions with length equal to either one or two elements. Micromagnetic simulations performed for 2 × 2 arrays of elements suggest that particular combinations of vortex chirality and polarization in neighboring elements are required to generate the observed magneto-optical contrast. [ABSTRACT FROM AUTHOR]

Time-resolved scanning Kerr microscopy (TRSKM) has been used to examine the effect of nonlocal spin transfer torque (NL-STT) within a two-terminal current perpendicular-to-plane nonlocal spin valve. A combination of Oersted field and NL-STT was used to excite and control the magnetization dynamics. By comparison with a macrospin model, the strength of the NL-STT was quantified and found to be comparable to that achieved by direct injection of spin-polarized current. The sensitivity of the magneto-optical probe to small out-of-plane deflections of the magnetization also allows the NL-STT to be quantified in quasi-dc measurements, greatly simplifying the investigation of STT phenomena. [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]

We have observed the eigenmodes of coupled transverse domain walls in a pair of ferromagnetic nanowires. Although the pair is coupled magnetostatically, its spectrum is determined by a combination of pinning by edge roughness and dipolar coupling of the two walls. Because the corresponding energy scales are comparable, the coupling can be observed only at the smallest wire separations. A model of the coupled wall dynamics reproduces the experiment quantitatively, allowing for comparisons with the estimated pinning and domain wall coupling energies. The results have significant implications for the dynamics of devices based on coupled domain walls. [ABSTRACT FROM AUTHOR]

Element-specific phase-resolved x-ray ferromagnetic resonance (FMR) was used to study spin pumping within Co50Fe50(3)/Cu(6)/Ni80Fe20(5) (thicknesses in nanometers) spin valve structures with large areas, so that edge effects typical of nanopillars used in standard magnetotransport experiments could be neglected. The phase of precession of the Co50Fe50 fixed layer was recorded as FMR was induced in the Ni80Fe20 free layer. The field dependence of the fixed layer phase contains a clear signature of spin transfer torque (STT) coupling due to spin pumping. Fitting the phase delay yields the spin-mixing conductance, the quantity that controls all spin transfer phenomena. The STT coupling is destroyed by insertion of Ta into the middle of the Cu layer. [ABSTRACT FROM AUTHOR]

An all-optical experiment long utilized to image phonons excited by ultrashort optical pulses has been applied to a magnetic sample. In addition to circular ripples due to surface acoustic waves, we observe an .Y-shaped pattern formed by propagating spin waves. The emission of spin waves from the optical pulse epicenter in the form of collimated beams is qualitatively reproduced by micromagnetic simulations. We explain the observed pattern in terms of the group velocity distribution of Damon-Eshbach magnetostatic spin waves in the reciprocal space and the wave vector spectrum of the focused ultrafast laser pulse. [ABSTRACT FROM AUTHOR]

Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (Ni81Fe19) layer in a Py/Cu/Cu75Mn25/Cu/Co multilayer to pump a pure ac spin current into the Cu75Mn25 and Co layers, and then directly probe the spin current within the Cu75Mn25 layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the Cu75Mn25 layer. [ABSTRACT FROM AUTHOR]

We have used time resolved scanning Kerr microscopy to image collective spin wave modes within a 2D array of magnetic nanoelements. Long wavelength spin waves are confined within the array as if it was a continuous element of the same size but with effective material properties determined by the structure of the array and its constituent nanoelements. The array is an example of a magnonic metamaterial, the demonstration of which provides new opportunities within the emerging field of magnonics.