Wide Field Imaging of Intrinsic Spin Fluctuations in van der Waals Ferromagnet by Spin Defects in Hexagonal Boron Nitride

Recently, spin defects in hexagonal boron nitride (hBN) have emerged as a prominent candidate for implementing state-of-the-art quantum sensing research with optimal spatial and field sensitivity. Many of these advantages result from the remarkable compatibility to device integration and improved versatility for establishing nanoscale proximity with objects of interest. Taking advantage of boron vacancy spin defects in hBN, here we report nanoscale quantum imaging of low-dimensional ferromagnetism sustained in Fe₃GeTe₂/hBN van der Waals heterostructures. Using spin relaxometry methods, we have observed spatially varying magnetic fluctuations in the exfoliated Fe₃GeTe₂ flake, whose magnitude reaches a peak value around the Curie temperature, in consistent with the expected ferromagnetic phase transition. Our results demonstrate the capability of two-dimensional spin defects of investigating local magnetic properties of layered materials in an accessible and precise way, providing new opportunities for developing next-generation, transformative quantum sensing metrology.