Critical fluctuation and noise spectra in two-dimensional Fe$_{3}$GeTe$_{2}$ magnets

TL;DR

This study uses nitrogen-vacancy centers in diamond to investigate critical magnetic fluctuations and noise spectra in 2D Fe₃GeTe₂ magnets, revealing a transition from 1/f noise near the critical temperature to white noise away from it.

Contribution

It introduces a novel quantum decoherence imaging method to analyze critical fluctuations and noise spectra in 2D magnets, providing insights into their critical behavior.

Findings

Critical fluctuations contribute to a temperature-dependent magnetic noise spectrum.

Near the critical temperature, the noise exhibits 1/f behavior, while away from it, it becomes white noise.

The crossover between noise types can be controlled by the sample-diamond distance.

Abstract

Critical fluctuations play a fundamental role in determining the spin orders for low-dimensional quantum materials, especially for recently discovered two-dimensional (2D) magnets. Here we employ the quantum decoherence imaging technique utilizing nitrogen-vacancy centers in diamond to explore the critical magnetic fluctuations and the associated temporal spin noise in van der Waals magnet $\rm{Fe_{3}GeTe_{2}}$. We show that the critical fluctuation contributes to a random magnetic field characterized by the noise spectra, which can be changed dramatically near the critical temperature $T_c$. A theoretical model to describe this phenomenon is developed, showing that the spectral density is characterized by a $1/f$ noise near the $T_c$, while away from this point it behaves like a white noise. The crossover at a certain temperature between these two situations is determined by changing of the distance between the sample and the diamond. This work provides a new way to study critical fluctuation and to extract some of the critical exponents, which may greatly deepen our understanding of criticality in a wide range of physical systems.