5 research outputs found
Detection of paramagnetic spins with an ultrathin van der Waals quantum sensor
Detecting magnetic noise from small quantities of paramagnetic spins is a
powerful capability for chemical, biochemical, and medical analysis. Quantum
sensors based on optically addressable spin defects in bulk semiconductors are
typically employed for such purposes, but the 3D crystal structure of the
sensor inhibits the sensitivity by limiting the proximity of the defects to the
target spins. Here we demonstrate the detection of paramagnetic spins using
spin defects hosted in hexagonal boron nitride (hBN), a van der Waals material
which can be exfoliated into the 2D regime. We first create negatively charged
boron vacancy (V) defects in a powder of ultrathin hBN nanoflakes
(~atomic monolayers thick on average) and measure the longitudinal spin
relaxation time () of this system. We then decorate the dry hBN nanopowder
with paramagnetic Gd ions and observe a clear quenching, under
ambient conditions, consistent with the added magnetic noise. Finally, we
demonstrate the possibility of performing spin measurements including
relaxometry using solution-suspended hBN nanopowder. Our results highlight the
potential and versatility of the hBN quantum sensor for a range of sensing
applications, and pave the way towards the realisation of a truly 2D,
ultrasensitive quantum sensor.Comment: 19 pages, 11 figure
Stray magnetic field imaging of thin exfoliated iron halides flakes
Magnetic van der Waals materials are often proposed for use in future
spintronic devices, aiming to leverage the combination of long-range magnetic
order and near-atomic thinness to produce energy-efficient components. One
class of material that has been discussed in this context are the iron halides
FeCl and FeBr, which are A-type antiferromagnets with strong uniaxial
magnetocrystalline anisotropy. However, despite characterization of the bulk
materials, the possibility for sustaining the magnetic behaviors that would
underpin such applications in thin flakes has not been investigated. In this
work, we use nitrogen-vacancy (NV) center microscopy to quantitatively image
magnetism in individual exfoliated flakes of these iron halides, revealing the
absence of magnetic remanence, a weak induced magnetization under bias field
and variable behavior versus temperature. We show that our results are
consistent with the antiferromagnetic behavior of the bulk material with a soft
ferromagnetic uncompensated layer, indicating that extended (m)
ferromagnetic domains are not sustained even at low temperatures (down to 4 K).
Finally, we find that the magnetic order is strongly affected by the sample
preparation, with a surprising diamagnetic order observed in a thin, hydrated
sample.Comment: 15 pages, 13 figure
Stray magnetic field imaging of thin exfoliated iron halides flakes
Magnetic van der Waals materials are often proposed for use in future spintronic devices, aiming to leverage the combination of long-range magnetic order and near-atomic thinness to produce energy-efficient components. One class of material that has been discussed in this context are the iron halides FeCl2 and FeBr2, which are A-type antiferromagnets with strong uniaxial magnetocrystalline anisotropy. However, despite characterization of the bulk materials, the possibility for sustaining the magnetic behaviors that would underpin such applications in thin flakes has not been investigated. In this work, we use nitrogen-vacancy center microscopy to quantitatively image magnetism in individual exfoliated flakes of these iron halides, revealing the absence of magnetic remanence, a weak induced magnetization under bias field, and variable behavior versus temperature. We show that our results are consistent with the antiferromagnetic behavior of the bulk material with a soft ferromagnetic uncompensated layer, indicating that extended (>1µm) ferromagnetic domains are not sustained even at low temperatures (down to 4 K). Finally, we find that the magnetic order is strongly affected by the sample preparation, with a surprising diamagnetic behavior observed in a thin, hydrated sample.<br/
Multi-species optically addressable spin defects in a van der Waals material
Optically addressable spin defects hosted in two-dimensional van der Waals
materials represent a new frontier for quantum technologies, promising to lead
to a new class of ultrathin quantum sensors and simulators. Recently, hexagonal
boron nitride (hBN) has been shown to host several types of optically
addressable spin defects, thus offering a unique opportunity to simultaneously
address and utilise various spin species in a single material. Here we
demonstrate an interplay between two separate spin species within a single hBN
crystal, namely boron vacancy defects and visible emitter spins. We
unambiguously prove that the visible emitters are spins and
further demonstrate room temperature coherent control and optical readout of
both spin species. Importantly, by tuning the two spin species into resonance
with each other, we observe cross-relaxation indicating strong inter-species
dipolar coupling. We then demonstrate magnetic imaging using the
defects, both under ambient and cryogenic conditions, and
leverage their lack of intrinsic quantization axis to determine the anisotropic
magnetic susceptibility of a test sample. Our results establish hBN as a
versatile platform for quantum technologies in a van der Waals host at room
temperature
Imaging current control of magnetization in Fe 3 GeTe 2 with a widefield nitrogen-vacancy microscope
International audienceAbstract Van der Waals (vdW) magnets are appealing candidates for realising spintronic devices that exploit current control of magnetization (e.g. switching or domain wall motion), but so far experimental demonstrations have been sparse, in part because of challenges associated with imaging the magnetization in these systems. Widefield nitrogen-vacancy (NV) microscopy allows rapid, quantitative magnetic imaging across entire vdW flakes, ideal for capturing changes in the micromagnetic structure due to an electric current. Here we use a widefield NV microscope to study the effect of current injection in thin flakes (∼10 nm) of the vdW ferromagnet Fe 3 GeTe 2 (FGT). We first observe current-reduced coercivity on an individual domain level, where current injection in FGT causes substantial reduction in the magnetic field required to locally reverse the magnetisation. We then explore the possibility of current-induced domain-wall motion, and provide preliminary evidence for such a motion under relatively low current densities, suggesting the existence of strong current-induced torques in our devices. Our results illustrate the applicability of widefield NV microscopy to imaging spintronic phenomena in vdW magnets, highlight the possibility of efficient magnetization control by direct current injection without assistance from an adjacent conductor, and motivate further investigations of the effect of currents in FGT and other vdW magnets