Wide field imaging of van der Waals ferromagnet Fe3GeTe2 by spin defects in hexagonal boron nitride

Abstract

Emergent color centers with accessible spins hosted by van der Waals materials have attracted substantial interest in recent years due to their significant potential for implementing transformative quantum sensing technologies. Hexagonal boron nitride (hBN) is naturally relevant in this context due to its remarkable ease of integration into devices consisting of low-dimensional materials. Taking advantage of boron vacancy spin defects in hBN, we report nanoscale quantum imaging of low-dimensional ferromagnetism sustained in Fe3GeTe2/hBN van der Waals heterostructures. Exploiting spin relaxometry methods, we have further observed spatially varying magnetic fluctuations in the exfoliated Fe3GeTe2 flake, whose magnitude reaches a peak value around the Curie temperature. Our results demonstrate the capability of spin defects in hBN of investigating local magnetic properties of layered materials in an accessible and precise way, which can be extended readily to a broad range of miniaturized van der Waals heterostructure systems.

Quantum Emitters in Hexagonal Boron Nitride

“…Such a correlative magnetic−temperature imaging capability opens interesting opportunities in condensed matter physics. Imaging of magnetic fluctuations has also been demonstrated, 64 taking advantage of the close sensor−sample proximity. Despite this rapid progress, V B − faces important limitations as an optically active spin defect.…”

“…This multitude of creation methods, a consequence of the simple monovacancy structure of the defect, allows for precise defect engineering and placement, for instance to couple V B – defects to photonic structures ,− and for sensing applications. Proof-of-principle demonstrations of quantum imaging have been reported, − using dense layers of V B – defects created by ion irradiation in thin hBN flakes, with the flake placed on top of a sample of interest. Example results are given in Figure e,f which show magnetic field and temperature images obtained by spatially mapping the ODMR spectrum of the hBN flake stacked onto a van der Waals magnetic flake.…”

Above-Room-Temperature Ferromagnetism in Thin van der Waals Flakes of Cobalt-Substituted Fe5GeTe2

“…Given the small dimension and low mass of exfoliated flakes, a sensitive probe of magnetism capable of room temperature operation is required to investigate thin CFGT flakes. Examples of such probes include magnetic force microscopy (MFM), magnetic optical Kerr effect (MOKE) microscopy, NV scanning probe microscopy, , and more recently, magnetic sensing with boron vacancy defect centers in hexagonal boron nitride. − In this work, we employed wide-field QMI with NV centers in diamond. Given its ability to detect magnetic fields with high sensitivity and high spatial resolution (diffraction-limited), the NV center in diamond realizes a powerful quantum sensor of the local magnetic field and hence provides an enabling tool for advancing condensed matter physics and materials science .…”

Greatly Enhanced Emission from Spin Defects in Hexagonal Boron Nitride Enabled by a Low-Loss Plasmonic Nanocavity

“…We circumvent this issue by using lithographically patterned waveguide-mediated microwave delivery. 33,34,37 A coplanar waveguide structure offers more efficient control of the defect spins with the "in-plane" orientation of the microwave fields driving the "out-of-plane" spins.…”