Observation of Ultra-low AC Susceptibility in Micro-magnets Using Quantum Diamond Microscope

TL;DR

This paper demonstrates a quantum diamond microscope capable of ultra-low AC susceptibility measurements in micro-magnets, offering high spatial resolution and sensitivity beyond traditional methods.

Contribution

It introduces a NV center-based quantum diamond microscope for mapping AC susceptibility at micron scales with femto-joule sensitivity, surpassing conventional susceptometers.

Findings

Achieved 1-micrometer spatial resolution in AC susceptibility mapping.

Measured dipole moment changes on the order of femto-joules per tesla.

Successfully mapped magnetic dynamics at frequencies up to several hundred kilohertz.

Abstract

AC susceptometry, unlike static susceptometry, offers a deeper insight into magnetic materials. By employing AC susceptibility measurements, one can glean into crucial details regarding magnetic dynamics. Nevertheless, traditional AC susceptometers are constrained to measuring changes in magnetic moments within the range of a few nano-joules per tesla. Additionally, their spatial resolution is severely limited, confining their application to bulk samples only. In this study, we introduce the utilization of a Nitrogen Vacancy (NV) center-based quantum diamond microscope for mapping the AC susceptibility of micron-scale ferromagnetic specimens. By employing coherent pulse sequences, we extract both magnitude and the phase of the field from samples within a field of view spanning 70 micro-meters while achieving a resolution of 1 micro-meter. Furthermore, we quantify changes in dipole moment on the order of a femto-joules per tesla induced by excitations at frequencies reaching several hundred kilohertz.