Spin dynamics characterization in magnetic dots

TL;DR

This study investigates the spin configurations and magnon dynamics in magnetic dots, revealing phase transitions from ferromagnetic to vortex states influenced by exchange coupling and size, with implications for magnetic properties at finite temperatures.

Contribution

It provides a comprehensive analysis of phase transitions and magnon modes in magnetic dots, including numerical and analytical calculations with dipolar interactions fully incorporated.

Findings

Identified phase boundary between ferromagnetic and vortex states.

Characterized magnon modes in both phases.

Explained magnon instability leading to phase transition.

Abstract

The spin structure in a magnetic dot, which is an example of a quantum few-body system, is studied as a function of exchange coupling strength and dot size with in the semiclassical approximation on a discrete lattice. As the exchange coupli ng is decreased or the size is increased, the ground state undergoes a phase cha nge from a single domain ferromagnet to a spin vortex. The line separating these two phases has been calculated numerically for small system sizes. %, and analytically for larger dots. The dipolar interaction has been fully included in our calculations. Magnon frequencies in such a dot have also been calculated in both phases by the linearized equation of motion method. These results have also been reproduced f rom the Fourier transform of the spin autocorrelation function. From the magnon Density Of States (DOS), it is possible to identify the magnetic phase of the dot. Furthermore, the magnon modes have been characterized for both the ferromagnetic and the vortex phase, and the magnon instability mechanism leading to the vortex-ferro transition has also been identified. The results can also be used to compute finite temperature magnetization or vort icity of magnetic dots.