Ferran Macià

Spin-wave interference patterns created by spin-torque nano-oscillators for memory and computation

Magnetization dynamics in nanomagnets has attracted broad interest since it was predicted that a dc current flowing through a thin magnetic layer can create spin-wave excitations. These excitations are due to spin momentum transfer, a transfer of spin angular momentum between conduction electrons and the background magnetization, that enables new types of information processing. Here we show how arrays of spin-torque nano-oscillators can create propagating spin-wave interference patterns of use for memory and computation. Memristic transponders distributed on the thin film respond to threshold tunnel magnetoresistance values, thereby allowing spin-wave detection and creating new excitation patterns. We show how groups of transponders create resonant (reverberating) spin-wave interference patterns that may be used for polychronous wave computation and information storage.

Stable magnetic droplet solitons in spin-transfer nanocontacts

Magnetic thin films with perpendicular magnetic anisotropy have localized excitations that correspond to reversed, dynamically precessing magnetic moments, which are known as magnetic droplet solitons. Fundamentally, these excitations are associated with an attractive interaction between elementary spin-excitations and have been predicted to occur in perpendicularly magnetized materials in the absence of damping. Although damping suppresses these excitations, it can be compensated by spin-transfer torques when an electrical current flows in nanocontacts to ferromagnetic thin films. Theory predicts the appearance of magnetic droplet solitons in nanocontacts at a threshold current and, recently, experimental signatures of droplet nucleation have been reported. However, to date, these solitons have been observed to be nearly reversible excitations, with only partially reversed magnetization. Here, we show that magnetic droplet solitons exhibit a strong hysteretic response in field and current, proving the existence of bistable states: droplet and non-droplet states. In the droplet soliton state we find that the magnetization in the contact is almost fully reversed. These observations, in addition to their fundamental interest, are important to understanding and controlling droplet motion, nucleation and annihilation.

Quantum magnetic deflagration in Mn12 acetate

We report controlled ignition of magnetization reversal avalanches by surface acoustic waves in a single crystal of

Direct Observation of a Localized Magnetic Soliton in a Spin-Transfer Nanocontact.

{\mathrm{Mn}}_{12}

Observation of droplet soliton drift resonances in a spin-transfer-torque nanocontact to a ferromagnetic thin film

acetate. Our data show that the speed of the avalanche exhibits maxima on the magnetic field at the tunneling resonances of

The role of thermal coupling on avalanches in manganites

{\mathrm{Mn}}_{12}

Direct imaging of delayed magneto-dynamic modes induced by surface acoustic waves

. Combined with the evidence of magnetic deflagration in

Tailoring the magnetodynamic properties of nanomagnets using magnetocrystalline and shape anisotropies

{\mathrm{Mn}}_{12}

Describing synchronization and topological excitations in arrays of magnetic spin torque oscillators through the Kuramoto model.

acetate [Y. Suzuki et al., Phys. Rev. Lett. 95, 147201 (2005)], this suggests a novel physical phenomenon: deflagration assisted by quantum tunneling.

Eddy current interactions in a ferromagnet-normal metal bilayer structure, and its impact on ferromagnetic resonance lineshapes

We report the direct observation of a localized magnetic soliton in a spin-transfer nanocontact using scanning transmission x-ray microscopy. Experiments are conducted on a lithographically defined 150 nm diameter nanocontact to an ultrathin ferromagnetic multilayer with perpendicular magnetic anisotropy. Element-resolved x-ray magnetic circular dichroism images show an abrupt onset of a magnetic soliton excitation localized beneath the nanocontact at a threshold current. However, the amplitude of the excitation ≃25° at the contact center is far less than that predicted (⪅180°), showing that the spin dynamics is not described by existing models.