Ferromagnetic behavior of non-stoichiometric ZnS microspheres with a nanoplate-netted surface

Abstract

Undoped ZnS microspheres with a size of 4-5 mm were produced using a hydrothermal method with different ratios of Zn and S precursors. Structural and morphological measurements show that the sphalerite ZnS microspheres have a cavity surface self-assembled with nanoplates with a thickness of 20-30 nm. Experimentally measured magnetic hysteresis curves for the undoped ZnS microspheres clearly indicate ferromagnetic behavior at room temperature with a saturation magnetization M s ¼ 3.66 and 1.566 memu g À1 for an atomic ratio of Zn to S equal to 0.966 and 1.32, respectively. The calculations based on density functional theory within the generalized gradient approximation + Hubbard U (GGA + U) approach demonstrated that the ZnS (111) surface with Zn vacancies produces a ferromagnetic state with a magnetic moment per unit cell of 2.0 m B ; the defective ZnS (111) surface with mixed Zn and S vacancies has a reduced magnetic moment of 1.12 m B because of the structural reconstruction, while the defective ZnS (111) surface with only S vacancies is non-magnetic. The observed weak ferromagnetism for the ZnS microspheres can be ascribed to the Zn vacancies and the cavity surface; the latter results in a large number of unsaturated bonds for the S and Zn atoms at the interfacial and surface regions. These studies will be helpful for understanding the d 0 ferromagnetism. Fig. 3 The XPS spectra of samples #1 and #2 (a). The Zn 2p3/2 spectra with Gaussian fitting of samples #1 (b) and #3 (c). The S 2p3/2 spectra with Gaussian fitting of samples #1 (d) and #3 (e).This journal is

Ultrathin NiFeS Nanomeshes with Sulfur Vacancy for Electrocatalytic Hydrogen Evolution

“…Moreover, the XPS spectra of the S 2p core level can be resolved into triple peaks, which were labeled as I, II and III (Figure d). The peaks of I and III were ascribed to S 2p1/2 and S 2p3/2, respectively, while the peak of II can be ascribed to the sulfur vacancies . The larger integrated intensity of II in NiFeS 1‐x UNM confirmed the existence of a larger number of sulfur vacancies.…”

“…The electrochemical capacitance measurements (Figure S6) showed that the electrochemical active surface areas (ECSA) of NiFeS 1‐x UNM (4.2 mF cm −2 ) were much larger than those of NiFeS NS (2.8 mF cm −2 ) as displayed in Figure e. This result proved that more active sites existed in NiFeS 1‐x UNM due to their ultrathin nanomesh structure . Notably, NiFeS 1‐x UNM still showed better performance than NiFeS NS after normalization to ECSA (Figure f and Figure S7), demonstrating that NiFeS 1‐x UNM owned higher intrinsic activity.…”

Magnetism of Kesterite Cu2ZnSnS4 Semiconductor Nanopowders Prepared by Mechanochemically Assisted Synthesis Method

“…Since at 300 K both the paramagnetic and diamagnetic components are linear with magnetic field, the low field increase of magnetization suggests an additional component contributing to the measured magnetization. We suppose that in addition to the paramagnetic and diamagnetic components discussed earlier, there is also an extra component in the pre-kesterite nanopowder that has originated from ferro/ferrimagnetic impurities linked to the precursor system or formed during the high energy ball milling (e.g., some likely left-over zinc sulfide ZnS reported to show d 0 ferromagnetism [20,21]). We note that such a situation has been widely encountered, for instance, in a series of gallium nitride-and antimonide-based magnetic semiconductors synthesized with magnetic transition metal concentrations close to the solubility limits [38][39][40].…”

“…Given the above observations and since one of the potential metal centers in kesterite is d-orbital magnetic, i.e., Cu 2+ with the formal 3d 9 configuration while the expected copper sites are nominally Cu 1+ with diamagnetic configuration 3d 10 , kesterites's magnetic properties may come to play a significant role in defining its fundamentals-under certain stoichiometry and synthesis conditions these two types of copper centers can coexist in the kesterite's lattice. In addition, the high propensity of kesterite to accommodate variable element stoichiometries, extended site occupancy/disorder features, and various defects makes its nanocrystalline forms the firm candidates for the so-called d 0 magnetism observed in many disordered/defected nanomaterials including formally diamagnetic zinc sulfide ZnS [20][21][22]. Therefore, the combination of nuclear magnetic resonance measurements sensitive to close range ordering and local field peculiarities with measurements of overall magnetism reflecting averaged magnetic fields may yield a comprehensive insight into the characteristics of kesterite.…”

Enhancement of Hydrogen Productions by Accelerating Electron-Transfers of Sulfur Defects in the CuS@CuGaS2 Heterojunction Photocatalysts

“…The peak at low binding energy (162.00 eV) corresponds to the Cu-S bond, and the peak at the high binding energy (165.28 eV) corresponds to the Ga-S bond [40]. Furthermore, the intermediate peak observed near 163.74 eV corresponds to sulfur vacancy, which is attributed to sulfur defects formed at the CuGaS2 or heterojunction interface [41]. These XPS results demonstrate the presence of structural defects on the heterojunction 0.5CuS@1.5CuGaS2 catalyst surface and predict that the site can act as a reactive site.…”