  van der Waals (vdW) magnets are receiving ever-growing attention nowadays due
to their significance in both fundamental research on low-dimensional magnetism
and potential applications in spintronic devices. High crystalline quality of
vdW magnets is key for maintaining intrinsic magnetic and electronic
properties, especially when exfoliated down to the 2D limit. Here,
ultrahigh-quality air-stable vdW CrSBr crystals are synthesized using the
direct vapor-solid synthesis method. The high single crystallinity and spatial
homogeneity have been thoroughly evidenced at length scales from sub-mm to
atomic resolution by X-ray diffraction, second harmonic generation, and
scanning transmission electron microscopy. More importantly, specific heat
measurements of these ultrahigh quality CrSBr crystals show three thermodynamic
anomalies at 185K, 156K, and 132K, revealing a stage-by-stage development of
the magnetic order upon cooling, which is also corroborated with the
magnetization and transport results. Our ultrahigh-quality CrSBr can further be
exfoliated down to monolayers and bilayers easily, paving the way to integrate
them into heterostructures for spintronic and magneto-optoelectronic
applications.
