Direct evidence for the source of reported magnetic behavior in “CoTe”

Abstract

In order to unambiguously identify the source of magnetism reported in recent studies of the Co-Te system, two sets of high-quality, epitaxial CoTex films (thickness ≈ 300 nm) were prepared by pulse laser deposition (PLD). X-ray diffraction (XRD) shows that all of the films are epitaxial along the [001] direction and have the hexagonal NiAs structure. There is no indication of any second phase metallic Co peaks (either fcc or hcp) in the XRD patterns. The two sets of CoTex films were grown on various substrates with PLD targets having Co:Te in the atomic ratio of 50:50 and 35:65. From the measured lattice parameters c = 5.396 Å for the former and c = 5.402 Å for the latter, the compositions CoTe1.71 (63.1% Te) and CoTe1.76 (63.8% Te), respectively, are assigned to the principal phase. Although XRD shows no trace of metallic Co second phase, the magnetic measurements do show a ferromagnetic contribution for both sets of films with the saturation magnetization values for the CoTe1.71 films being approximately four times the values for the CoTe1.76 films. 59 Co spin-echo nuclear magnetic resonance (NMR) clearly shows the existence of metallic Co inclusions in the films. The source of weak ferromagnetism reported in several recent studies is due to the presence of metallic Co, since the stoichiometric composition "CoTe" does not exist.

Energy Harvesting from Atomically Thin Co2Te3

“…Figure b shows the X-ray diffraction (XRD) patterns of the bulk and exfoliated Co 2 Te 3 . The peaks match well with the hexagonal crystal structure and the lattice parameters a = b = 3.8427 Å and c = 5.3794 Å and α = β = 90° and γ = 120° and in good agreement with the reported literature . For bulk Co 2 Te 3 , the maxima of the profile intensity occur at the (101), (002), (102), (110), (201), (103), and (202) diffraction peaks (see Figure b, bottom).…”

“…The peaks match well with the hexagonal crystal structure and the lattice parameters a = b = 3.8427 Å and c = 5.3794 Å and α = β = 90°and γ = 120°and in good agreement with the reported literature. 26 For bulk Co 2 Te 3 , the maxima of the profile intensity occur at the (101), (002), (102), (110), (201), (103), and (202) diffraction peaks (see Figure 1b, bottom). As noted in Figure 1b, peaks of (100), (101), (002), (102), (110), and (103) were observed in the 2D Co 2 Te 3 .…”

Emerging 2D Cobalt Telluride (CoxTey): from Theory to Applications

“…164) metallic Ref. 28 CoTe 2 a = 5.314 Å, b = 6.320 Å and c = 3.882 Å Orthorhombic, space group Pnnm metallic Ref. 17 as Ni 2 In structure with the space group 63/mmc.…”

“…After optimizing the substrate temperature, the thickness of Co x Te y film could be manifested simply by the impacting circles or durations of laser pulse. [28,64]…”

“…[22,23,24,25] Differentiating from traditional vdW magnets, the stoichiometric ratio of Co and Te varies from (1+𝛿):1 to 1:2 and the variation of crystal structure effectively modulates the band structure of Co x Te y from type-II Dirac semimetallic (1T-CoTe 2 ) to semiconducting (bandgap ≈2.5 eV, CoTe). [26,27,28] This extra degree of freedom enables Co x Te y taking centerstage for exploring spin fluctuation and other new physical paradigms. Until now, a comprehensive overview of Co x Te y in terms of magnetic and electronic properties is still lacking, severely restricting its expansion to device applications.…”