14 research outputs found
Electrical and thermal generation of spin currents by magnetic bilayer graphene
Ultracompact spintronic devices greatly benefit from the implementation of two-dimensional materials that provide large spin polarization of charge current together with long-distance transfer of spin information. Here spin-transport measurements in bilayer graphene evidence a strong spin–charge coupling due to a large induced exchange interaction by the proximity of an interlayer antiferromagnet (CrSBr). This results in the direct detection of the spin polarization of conductivity (up to 14%) and a spin-dependent Seebeck effect in the magnetic graphene. The efficient electrical and thermal spin–current generation is the most technologically relevant aspect of magnetism in graphene, controlled here by the antiferromagnetic dynamics of CrSBr. The high sensitivity of spin transport in graphene to the magnetization of the outermost layer of the adjacent antiferromagnet, furthermore, enables the read-out of a single magnetic sublattice. The combination of gate-tunable spin-dependent conductivity and Seebeck coefficient with long-distance spin transport in a single two-dimensional material promises ultrathin magnetic memory and sensory devices based on magnetic graphene
Layered Antiferromagnetism Induces Large Negative Magnetoresistance in the van der Waals Semiconductor CrSBr
The recent discovery of magnetism within the family of exfoliatable van der
Waals (vdW) compounds has attracted considerable interest in these materials
for both fundamental research and technological applications. However current
vdW magnets are limited by their extreme sensitivity to air, low ordering
temperatures, and poor charge transport properties. Here we report the magnetic
and electronic properties of CrSBr, an air-stable vdW antiferromagnetic
semiconductor that readily cleaves perpendicular to the stacking axis. Below
its N\'{e}el temperature, K, CrSBr adopts an A-type
antiferromagnetic structure with each individual layer ferromagnetically
ordered internally and the layers coupled antiferromagnetically along the
stacking direction. Scanning tunneling spectroscopy and photoluminescence (PL)
reveal that the electronic gap is eV with a
corresponding PL peak centered at eV. Using magnetotransport
measurements, we demonstrate strong coupling between magnetic order and
transport properties in CrSBr, leading to a large negative magnetoresistance
response that is unique amongst vdW materials. These findings establish CrSBr
as a promising material platform for increasing the applicability of vdW
magnets to the field of spin-based electronics
Exchange bias between van der Waals materials: tilted magnetic states and field-free spin-orbit-torque switching
Magnetic van der Waals heterostructures provide a unique platform to study
magnetism and spintronics device concepts in the two-dimensional limit. Here,
we report studies of exchange bias from the van der Waals antiferromagnet CrSBr
acting on the van der Waals ferromagnet Fe3GeTe2 (FGT). The orientation of the
exchange bias is along the in-plane easy axis of CrSBr, perpendicular to the
out-of-plane anisotropy of the FGT, inducing a strongly tilted magnetic
configuration in the FGT. Furthermore, the in-plane exchange bias provides
sufficient symmetry breaking to allow deterministic spin-orbit torque switching
of the FGT in CrSBr/FGT/Pt samples at zero applied magnetic field. A minimum
thickness of the CrSBr greater than 10 nm is needed to provide a non-zero
exchange bias at 30 K
Designing magnetic properties in CrSBr through hydrostatic pressure and ligand substitution
The ability to control magnetic properties of materials is crucial for
fundamental research and underpins many information technologies. In this
context, two-dimensional materials are a particularly exciting platform due to
their high degree of tunability and ease of implementation into nanoscale
devices. Here we report two approaches for manipulating the A-type
antiferromagnetic properties of the layered semiconductor CrSBr through
hydrostatic pressure and ligand substitution. Hydrostatic pressure compresses
the unit cell, increasing the interlayer exchange energy while lowering the
N\'eel temperature. Ligand substitution, realized synthetically through Cl
alloying, anisotropically compresses the unit cell and suppresses the
Cr-halogen covalency, reducing the magnetocrystalline anisotropy energy and
decreasing the N\'eel temperature. A detailed structural analysis combined with
first-principles calculations reveal that alterations in the magnetic
properties are intricately related to changes in direct Cr-Cr exchange
interactions and the Cr-anion superexchange pathways. Further, we demonstrate
that Cl alloying enables chemical tuning of the interlayer coupling from
antiferromagnetic to ferromagnetic, which is unique amongst known
two-dimensional magnets. The magnetic tunability, combined with a high ordering
temperature, chemical stability, and functional semiconducting properties, make
CrSBr an ideal candidate for pre- and post-synthetic design of magnetism in
two-dimensional materials.Comment: Main text: 17 pages, 4 figures. Supporting Information: 34 pages, 32
figures, 4 table
Hidden low-temperature magnetic order revealed through magnetotransport in monolayer CrSBr
Magnetic semiconductors are a powerful platform for understanding, utilizing
and tuning the interplay between magnetic order and electronic transport.
Compared to bulk crystals, two-dimensional magnetic semiconductors have greater
tunability, as illustrated by the gate modulation of magnetism in exfoliated
CrI and CrGeTe, but their electrically insulating properties
limit their utility in devices. Here we report the simultaneous electrostatic
and magnetic control of electronic transport in atomically-thin CrSBr, an
A-type antiferromagnetic semiconductor. Through magnetotransport measurements,
we find that spin-flip scattering from the interlayer antiferromagnetic
configuration of multilayer flakes results in giant negative magnetoresistance.
Conversely, magnetoresistance of the ferromagnetic monolayer CrSBr vanishes
below the Curie temperature. A second transition ascribed to the ferromagnetic
ordering of magnetic defects manifests in a large positive magnetoresistance in
the monolayer and a sudden increase of the bulk magnetic susceptibility. We
demonstrate this magnetoresistance is tunable with an electrostatic gate,
revealing that the ferromagnetic coupling of defects is carrier mediated
New material connections in a mother-of-pearl Enconchado from the Viceroyalty of New Spain
Abstract Adoration of the Magi (ca. 1695–1700), an enconchado painting attributed to Miguel González, active in Mexico in the late seventeenth century, exemplifies the refinement of the arts produced in Spanish America as a response to the taste for Asian goods during the seventeenth and eighteenth centuries. The painting and its original mother-of-pearl inlaid frame were examined and analyzed using non-invasive and micro-sampling methods, an approach that permitted answering outstanding questions about the stratigraphy, pigments, and the use of shells throughout the painting and frame. The identification of the mother-of-pearl, determined to be from a Pinctada species, was a central focus of this study. In addition to the inlaid shells in the painting and frame, shell fragments were observed mixed with gypsum in the ground preparation of the painting by SEM–EDS. To our knowledge, this is a novel identification of marine shells in the ground of an easel painting. Traces of workmanship in the inlaid shells observed by SEM and optical microscopy are possibly connected to pre-Hispanic methodologies of mother-of-pearl refinement. Graphical Abstrac