Core-Core Dynamics in Spin Vortex Pairs

TL;DR

This paper explores the dynamics of spin vortex pairs in magnetic nano-pillars, revealing how strong core-core coupling leads to collective resonances that could enable advanced nanoscale storage technologies.

Contribution

It provides the first detailed experimental, analytical, and numerical analysis of the 16 ground states and their dynamics in vortex-pair systems, highlighting the impact of core-core coupling.

Findings

Identification of 16 vortex-pair ground states

Observation of collective resonances in GHz range due to core coupling

Potential applications in ultra-dense magnetic storage

Abstract

We investigate magnetic nano-pillars, in which two thin ferromagnetic nanoparticles are separated by a nanometer thin nonmagnetic spacer and can be set into stable spin vortex-pair configurations. The 16 ground states of the vortex-pair system are characterized by parallel or antiparallel chirality and parallel or antiparallel core-core alignment. We detect and differentiate these individual vortex-pair states experimentally and analyze their dynamics analytically and numerically. Of particular interest is the limit of strong core-core coupling, which we find can dominate the spin dynamics in the system. We observe that the 0.2 GHz gyrational resonance modes of the individual vortices are replaced with 2-6 GHz range collective rotational and vibrational core-core resonances in the configurations where the cores form a bound pair. These results demonstrate new opportunities in producing and manipulating spin states on the nanoscale and may prove useful for new types of ultra-dense storage devices where the information is stored as multiple vortex-core configurations.