Magnetic Droplet: When a solitary wave travels atop the surface of a fluid, its shape generally changes with time, with some of its components traveling at velocities slightly different than others. In nonlinear media, this spreading effect may be countered by a slimming effect stemming from the non-linearity, which generates an object with perfectly preserved shape, called a soliton. Solitons have been observed in fluids, granular media, and other systems. Mohseni et al. (p. 1295 ) detected a dissipative soliton (one that also balances gain and dissipation) in a magnetic system, in the form of a magnetic droplet consisting of a core of spins pointing opposite to the external magnetic field. The droplet exhibited peculiar dynamics and could be controlled by electric current.

Spin–torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin–torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin–torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top–down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin–torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin–torque oscillators and pairwise synchronization in devices with four and five nanocontacts.

It has been argued that if multiple spin wave modes are competing for the same centrally located energy source, as in a nanocontact spin torque oscillator, that only one mode should survive in the steady state. Here, the experimental conditions necessary for mode coexistence are explored. Mode coexistence is facilitated by the local field asymmetries induced by the spatially inhomogeneous Oersted field, which leads to a physical separation of the modes, and is further promoted by spin wave localization at reduced applied field angles. Finally, both simulation and experiment reveal a low frequency signal consistent with the intermodulation of two coexistent modes.

We investigate exchange coupled ${\left[\text{Co}/\text{Pd}\right]}_5–\text{NiFe}$ thin films. Due to competition between the in-plane shape anisotropy of the NiFe and strong perpendicular magnetic anisotropy of the ${\left[\text{Co}/\text{Pd}\right]}_5$ multilayer, unique magnetic configurations are achievable. In particular, we explore the out-of-plane magnetization tilt angle of the NiFe layer. Experimental results, based on conventional magnetometry, ferromagnetic resonance, and magnetic force microscopy, agree well with one-dimensional micromagnetic simulations. We find that the tilt angle is highly tunable (0°–60°) over a small range of NiFe thicknesses (4.8–8 nm). Potential applications for high power, zero-field operation spin torque oscillators are discussed.

We demonstrate a nano‐contact based spin‐torque oscillator (STO) combining a high operating frequency with low field operation. The STO is based on an orthogonal spin‐valve architecture with an in‐plane Co polarizer and an out‐of‐plane Co/Ni multilayer free layer. High frequency operation at low external fields is achieved by tailoring the Co/Ni layer properties to increase the strength (H_k) of the perpendicular magnetic anisotropy, while simultaneously reducing the saturation magnetization (M_s). Our approach emphasizes the importance of μ₀(H_k–M_s) in determining the operating frequency in this system, and suggests that yet higher frequencies should be attainable through further optimization. magnified image