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Register a new userRobust intrinsic ferromagnetism in 2D half-metallic material MnAsS$_4$
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Two-dimensional (2D) intrinsic half-metallic materials are of great interest to explore the exciting physics and applications of nanoscale spintronic devices, but no such materials have been experimentally realized. Using first-principles calculations based on density-functional theory (DFT), we predicted that single-layer MnAsS$_4$ was a 2D intrinsic ferromagnetic (FM) half-metal. The half-metallic spin gap for single-layer MnAsS$_4$ is about 1.46 eV, and it has a large spin splitting of about 0.49 eV in the conduction band. Monte Carlo simulations predicted the Curie temperature (emph{T}$_c$) was about 740 K. Moreover, Within the biaxial strain ranging from -5% to 5%, the FM half-metallic properties remain unchanged. Its ground-state with 100% spin-polarization ratio at Fermi level may be a promising candidate material for 2D spintronic applications.
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In recent years, intrinsic two-dimensional (2D) magnetism aroused great interest because of its potential application in spintronic devices. However, low Curie temperature (emph{T}$_c$) and magnetic anisotropy energy (MAE) limit its application prospects. Here, using first-principles calculations based on density-functional theory (DFT), we predicted a series of stable MnXSe$_4$ (X=As, Sb) single-layer. The MAE of single-layer MnAsSe$_4$ and MnSbSe$_4$ was 648.76 and 808.95 ${mu}$eV per Mn atom, respectively. Monte Carlo (MC) simulations suggested the emph{T}$_c$ of single-layer MnAsSe$_4$ and MnSbSe$_4$ was 174 and 250 K, respectively. The energy band calculation with hybrid Heyd-Scuseria-Ernzerhof (HSE06) function indicated the MnXSe$_4$ (X = As, Sb) were ferromagnetic (FM) half-metallic. Also it had 100% spin-polarization ratio at the Fermi level. For MnAsSe$_4$ and MnSbSe$_4$, the spin-gap were 1.59 and 1.48 eV, respectively. These excellent magnetic properties render MnXSe$_4$ (X = As, Sb) promising candidate materials for 2D spintronic applications.
Next-generation spintronic devices will benefit from low-dimensionality, ferromagnetism, and half-metallicity, possibly controlled by electric fields. We find these technologically-appealing features to be combined with an exotic microscopic origin of magnetism in doped CdOHCl, a van der Waals material from which 2D layers may be exfoliated. By means of first principles simulations, we predict homogeneous hole-doping to give rise to $p$-band magnetism in both the bulk and monolayer phases and interpret our findings in terms of Stoner instability: as the Fermi level is tuned via hole-doping through singularities in the 2D-like density of states, ferromagnetism develops with large saturation magnetization of 1 $mu_B$ per hole, leading to a half-metallic behaviour for layer carrier densities of the order of 10$^{14}$ cm$^{-2}$. Furthermore, we put forward electrostatic doping as an additional handle to induce magnetism in monolayers and bilayers of CdOHCl. Upon application of critical electric fields perpendicular to atomically-thin-films (as low as 0.2 V/$A{deg}$ and 0.5 V/$A{deg}$ in the bilayer and monolayer case, respectively), we envisage the emergence of a magnetic half-metallic state. The different behaviour of monolayer vs bilayer systems, as well as an observed asymmetric response to positive and negative electric fields in bilayers, are interpreted in terms of intrinsic polarity of CdOHCl atomic stacks, a distinctive feature of the material. In perspective, given the experimentally accessible magnitude of critical fields in bilayer of CdOHCl, one can envisage $p$ band magnetism to be exploited in miniaturized spintronic devices.
Using first-principles calculations, the electronic and magnetic properties of orthorhombic BaFeO$_{3}$ (BFO) are investigated with local spin density approximation (LSDA). The calculations reveal that at the optimized lattice volume BFO has a lower energy in ferromagnetic state as compared with antiferromagnetic state. At the equilibrium volume, BFO shows metallic behavior, however, under a large tensile strain ($sim25%$), BFO shows half-metallic behavior consistent with the integer magnetic moment of $4.0mu_{rm{B}}$/fu mainly caused by the $t_{2g}$ and $e_{g}$ electrons of Fe. Including a Hubbard-like contribution $U$ (LSDA$+U$) on Fe $d$ states induced half-metallic bahvior without external strain, which indicates that $U$ can be used to tune the electronic structure of BFO. The magnetic moments remained robust against $sim 10%$ compressive and tensile strain. At large compressive (tensile) strain, the half-metallicity of BFO is mainly destroyed by the Fe-$d$ (O-$p$) electrons in agreement with the non-integer value of the magnetic moments of BFO.
We have synthesized unique colloidal nanoplatelets of the ferromagnetic two-dimensional (2D) van der Waals material CrI3 and have characterized these nanoplatelets structurally, magnetically, and by magnetic circular dichroism spectroscopy. The isolated CrI3 nanoplatelets have lateral dimensions of ~25 nm and ensemble thicknesses of only ~4 nm, corresponding to just a few CrI3 monolayers. Magnetic and magneto-optical measurements demonstrate robust 2D ferromagnetic ordering in these nanoplatelets with Curie temperatures similar to those observed in bulk CrI3, despite the strong spatial confinement. These data also show magnetization steps akin to those observed in micron-sized few-layer 2D sheets and associated with concerted spin-reversal of individual CrI3 layers within few-layer van der Waals stacks. Similar data have also been obtained for CrBr3 and anion-alloyed Cr(I1-xBrx)3 nanoplatelets. These results represent the first example of laterally confined 2D van der Waals ferromagnets of any composition. The demonstration of robust ferromagnetism at nanometer lateral dimensions opens new doors for miniaturization in spintronics devices based on van der Waals ferromagnets.
Intrinsic anomalous Nernst effect (ANE), like its Hall counterpart, is generated by Berry curvature of electrons in solids. Little is known about its response to disorder. In contrast, the link between the amplitude of the ordinary Nernst coefficient and the mean-free-path is extensively documented. Here, by studying Co$_3$Sn$_2$S$_2$, a topological half-metallic semimetal hosting sizable and recognizable ordinary and anomalous Nernst responses, we demonstrate an anti-correlation between the amplitude of ANE and carrier mobility. We argue that the observation, paradoxically, establishes the intrinsic origin of the ANE in this system. We conclude that various intrinsic off-diagonal coefficients are set by the way the Berry curvature is averaged on a grid involving the mean-free-path, the Fermi wavelength and the de Broglie thermal length.
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