A model for individual quantal nano-skyrmions

Abstract

A quantal model description of a discrete localized skyrmion singularity embedded in a ferromagnetic environment is proposed. It allows discussing the importance of various parameters in the appearance of a quantal skyrmion singularity. Analysis of the skyrmion reveals a few specific quantal properties: presence of a whole series of skyrmion states, nonclassical nature of the local spins, presence of superposition states and presence of extraskyrmion states due to the quantization of the central spin of the singularity. The interaction of an electron, tunneling or substrate, with the skyrmion is also described allowing a new view at the origin of the skyrmion stability as well as the possibility to discriminate between ferromagnetic and skyrmion phase in an Inelastic Electron Tunneling Spectroscopy (IETS) experiment, based on the skyrmion quantal properties.

Controlled Creation of Quantum Skyrmions

“…In agreement with Ref. [26], we find a shift of the skyrmion ground states to smaller D if the system size is increased. Adiabatic creation of a quantum skyrmions.-In a classical magnetic system, a magnetic skyrmion can be created by a rotation of the magnetization of one of the sample's edge [18].…”

“…On the other hand, quantum tunneling can open decay channels from a stable to an unstable skyrmion configuration [24]. A purely quantum mechanical treatment could numerically identify quantum skyrmions in systems with Dzyaloshinkii-Moriya interactions (DMI) [25,26] and in frustrated ferromagnets [27] even without chiral interactions. Quantum skyrmions have so far been defined by an adapted classical lattice topological charge [28] using spin expectation values [26], or by spin triple products [25].…”

“…A purely quantum mechanical treatment could numerically identify quantum skyrmions in systems with Dzyaloshinkii-Moriya interactions (DMI) [25,26] and in frustrated ferromagnets [27] even without chiral interactions. Quantum skyrmions have so far been defined by an adapted classical lattice topological charge [28] using spin expectation values [26], or by spin triple products [25]. Beyond the investigation of ground state properties, tunneling between quantum skyrmion and ferromagnetic states due to the interaction with electrons has been studied [26].…”

“…Quantum skyrmions have so far been defined by an adapted classical lattice topological charge [28] using spin expectation values [26], or by spin triple products [25]. Beyond the investigation of ground state properties, tunneling between quantum skyrmion and ferromagnetic states due to the interaction with electrons has been studied [26]. While the transition probabilities between those two configurations are addressed, a reliable procedure for creating quantum skyrmions has not been proposed so far.…”

“…A potential realization of the model are nanoskyrmions in Pd/Fe/Ir(111) islands decorated by ferromagnetic Co [32]. Quantum skyrmions.-The question how to define a skyrmion on a quantum spin lattice has been extensively discussed [25][26][27]. Here, in analogy to Gauyacq et al [26], we use two quantities with different purposes, both approaching the lattice topological charge [28] if the quantum spins were replaced by classical magnetic moments, namely…”