# Ising-like dynamics and frozen states in systems of ultrafine magnetic particles

## TL;DR

This study uses Monte-Carlo simulations to explore aging and spin-glass phases in ultrafine magnetic particles, revealing Ising-like behavior, frozen antiparallel chains, and unexpected effects of order on aging phenomena.

## Contribution

It demonstrates that magnetic moments in nanoparticle systems behave like Ising spins, with aging phenomena influenced by dipolar interactions and structural order, providing new insights into magnetic glassy states.

## Key findings

- Magnetic moments align parallel to anisotropy axes.
- Aging phenomena are more pronounced in ordered structures.
- Frozen antiparallel chain-like patterns emerge at low temperatures.

## Abstract

We use Monte-Carlo simulations to study aging phenomena and the occurence of spinglass phases in systems of single-domain ferromagnetic nanoparticles under the combined influence of dipolar interaction and anisotropy energy, for different combinations of positional and orientational disorder. We find that the magnetic moments oriente themselves preferably parallel to their anisotropy axes and changes of the total magnetization are solely achieved by 180 degree flips of the magnetic moments, as in Ising systems. Since the dipolar interaction favorizes the formation of antiparallel chain-like structures, antiparallel chain-like patterns are frozen in at low temperatures, leading to aging phenomena characteristic for spin-glasses. Contrary to the intuition, these aging effects are more pronounced in ordered than in disordered structures.