In a conventional magnetic material, a long-range magnetic
order
develops in three dimensions, and reducing a layer number weakens
its magnetism. Here we demonstrate anomalous layer-number-independent
ferromagnetism down to the two-dimensional (2D) limit in a metastable
phase of Cr3Te4. We fabricated Cr3Te4 thin films by molecular-beam epitaxy and found that
Cr3Te4 could host two distinct ferromagnetic
phases characterized with different Curie temperatures (T
C). One is the bulk-like “high-T
C phase” showing room-temperature ferromagnetism,
which is consistent with previous studies. The other is the metastable
“low-T
C phase” with T
C ≈ 160 K, which exhibits a layer-number-independent T
C down to the 2D limit in marked contrast with
the conventional high-T
C phase, demonstrating
a purely 2D nature of its ferromagnetism. Such significant differences
between two distinct phases could be attributed to a small variation
in the doping level, making this material attractive for future ultracompact
spintronics applications with potential gate-tunable room-temperature
2D ferromagnetism.
Magnetocrystalline anisotropy, a
key ingredient for establishing
long-range order in a magnetic material down to the two-dimensional
(2D) limit, is generally associated with spin–orbit interaction
(SOI) involving a finite orbital angular momentum. Here we report
strong out-of-plane magnetic anisotropy without orbital angular momentum,
emerging at the interface between two different van der Waals (vdW)
materials, an archetypal metallic vdW material NbSe2 possessing
Zeeman-type SOI and an isotropic vdW ferromagnet V5Se8. We found that the Zeeman SOI in NbSe2 induces
robust out-of-plane magnetic anisotropy in V5Se8 down to the 2D limit with a more than 2-fold enhancement of the
transition temperature. We propose a simple model that takes into
account the energy gain in NbSe2 in contact with a ferromagnet,
which naturally explains our observations. Our results demonstrate
a conceptually new magnetic proximity effect at the vdW interface,
expanding the horizons of emergent phenomena achievable in vdW heterostructures.
The present work reports a modification in the design of the previously known Ag/Ag 2 S neuron-inspired devices by the addition of a modulating layer of graphene oxide (GO). The Ag 2 S/GO structures were fabricated with a simple yet effective method consisting of the sulfurization of highpurity silver wires dip-coated in GO solution. The structure was observed to maintain the switching characteristics of Ag 2 S, but also to exhibit tunneling OFF state currents modulated by the GO thin film layer. This result was also confirmed through the direct observation of the Ag 2 S/GO surface with a scanning electron microscope. The notable volatility-based neuromorphic properties observed in Ag 2 S were enhanced in the presence of GO, and a switching model is proposed considering the present experimental results. The ultra-thin insulating nature of GO emphasizes its potential modulating capabilities, and the results suggest that GO may be an important addition for future electrochemical resistive switching based neuron-inspired devices.
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