AC magnetometry of van der Waals magnets using ultrasensitive Graphene Hall sensors

TL;DR

This paper demonstrates highly sensitive AC and DC magnetometry of 2D ferromagnetic materials using graphene Hall sensors, enabling detailed magnetic property measurements at nanoscale with record sensitivity.

Contribution

It introduces a novel graphene Hall sensor platform with record-low noise for quantitative magnetic measurements of 2D materials, including AC susceptibility up to 1 kHz.

Findings

Record-low magnetic field detection noise achieved.

First AC susceptibility measurement in a van der Waals magnet.

Graphene Hall sensors enable sensitive studies of 2D magnetic phases.

Abstract

Probing the dynamical magnetic properties of two-dimensional (2D) materials requires sensitive techniques capable of detecting small magnetic fields from nanoscale samples. We demonstrate quantitative AC and DC magnetometry of a ferromagnetic Fe3-xGeTe2 nanoflakes using ultrasensitive graphene Hall sensors. These devices achieve record-low magnetic field detection noise at both cryogenic and room temperature, enabled by hBN encapsulation, low-resistance fluorographene contacts, and a novel fabrication process. We perform quantitative AC susceptibility measurements up to 1 kHz, resolving both real and imaginary components with nanotesla-scale sensitivity and milliradian phase accuracy, the first such measurement in a van der Waals magnet. Our results establish graphene Hall sensors as a powerful and broadly applicable platform for studying magnetic and superconducting phases near the 2D limit.