An official website of the United States government
Abstract Magnetic van der Waals (vdW) materials are a promising platform for producing atomically thin spintronic and optoelectronic devices. The A‐type antiferromagnet CrSBr has emerged as a particularly exciting material due to its high magnetic ordering temperature, semiconducting electrical properties, and enhanced chemical stability compared to other vdW magnets. Exploring mechanisms to tune its magnetic properties will facilitate the development of nanoscale devices based on vdW materials with designer magnetic properties. Here it is investigated how the magnetic properties of CrSBr change under pressure and ligand substitution. Pressure compresses the unit cell, increasing the interlayer exchange energy while lowering the Néel temperature. Ligand substitution, realized synthetically through Cl alloying, anisotropically compresses the unit cell and suppresses the Cr‐halogen covalency, reducing the magnetocrystalline anisotropy energy and decreasing the Néel temperature. A detailed structural analysis combined with first‐principles calculations reveals that alterations in the magnetic properties are intricately related to changes in direct Cr–Cr exchange interactions and the Cr–anion superexchange pathways. Further, it is demonstrated that Cl alloying enables chemical tuning of the interlayer coupling from antiferromagnetic to ferromagnetic, which is unique among known two‐dimensional magnets.
more »
« less
Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets
Van der Waals (VdW) materials have opened new directions in the study of low dimensional magnetism. A largely unexplored arena is the intrinsic tuning of VdW magnets toward new ground states. Chromium trihalides provided the first such example with a change of interlayer magnetic coupling emerging upon exfoliation. Here, we take a different approach to engineer previously unknown ground states, not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the nonmagnetic ligand atoms (Cl, Br, I). We synthesize a three-halide series, CrCl 3 − x − y Br x I y , and map their magnetic properties as a function of Cl, Br, and I content. The resulting triangular phase diagrams unveil a frustrated regime near CrCl 3 . First-principles calculations confirm that the frustration is driven by a competition between the chromium and halide SOCs. Furthermore, we reveal a field-induced change of interlayer coupling in the bulk of CrCl 3 − x − y Br x I y crystals at the same field as in the exfoliation experiments.
more »
« less
- PAR ID:
- 10175673
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 6
- Issue:
- 30
- ISSN:
- 2375-2548
- Page Range / eLocation ID:
- eabb9379
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract We incorporate Se into the 3D halide perovskite framework using the zwitterionic ligand: SeCYS (+NH3(CH2)2Se−), which occupies both the X−and A+sites in the prototypical ABX3perovskite. The new organoselenide‐halide perovskites: (SeCYS)PbX2(X=Cl, Br) expand upon the recently discovered organosulfide‐halide perovskites. Single‐crystal X‐ray diffraction and pair distribution function analysis reveal the average structures of the organoselenide‐halide perovskites, whereas the local lead coordination environments and their distributions were probed through solid‐state77Se and207Pb NMR, complemented by theoretical simulations. Density functional theory calculations illustrate that the band structures of (SeCYS)PbX2largely resemble those of their S analogs, with similar band dispersion patterns, yet with a considerable band gap decrease. Optical absorbance measurements indeed show band gaps of 2.07 and 1.86 eV for (SeCYS)PbX2with X=Cl and Br, respectively. We further demonstrate routes to alloying the halides (Cl, Br) and chalcogenides (S, Se) continuously tuning the band gap from 1.86 to 2.31 eV–straddling the ideal range for tandem solar cells or visible‐light photocatalysis. The comprehensive description of the average and local structures, and how they can fine‐tune the band gap and potential trap states, respectively, establishes the foundation for understanding this new perovskite family, which combines solid‐state and organo‐main‐group chemistry.more » « less
-
Inversion symmetry breaking could lead to the creation of a Rashba–Dresselhauls magnetic field, which plays the key role in spintronic devices. In this work, we propose and develop a composition gradient engineering approach that breaks inversion symmetry into inorganic halide perovskites with strong spin–orbit coupling. We synthesize epitaxial CsPbBr x Cl (3− x ) with Br/Cl composition gradient by a two-step chemical vapor deposition approach. Through optoelectronic measurements, we show the presence of circular photogalvanic effects (CPGEs), evidencing a Rashba-like spin polarized band structure. By spatially resolved photoluminescence spectra, we find that the observed CPGE is likely a cumulative result of inversion symmetry-broken interfaces featured by abrupt and stepwise composition gradient between the pristine and separated daughter phases. Our work suggests an avenue in engineering the spintronic property of halide perovskites for information processing.more » « less
-
Triple cation Cs/methylammonium (MA)/formamidinium (FA) and double halide Br/I lead perovskites improved the stability and efficiency of perovskite solar cells (PVSCs). However, their effects on alloyed Pb–Sn perovskites are unexplored. In this work, perovskite thin films with the composition Cs x (MA 0.17 FA 0.83 ) 1−x Pb 1−y Sn y (I 0.83 Br 0.17 ) 3 are synthesized utilizing a one-step solution process plus an anti-solvent wash technique and deployed in PVSCs with an inverted architecture. All films show a cubic crystal structure, demonstrating that compositional tuning of both the tolerance factor and crystallization rate allows for dense, single phase formation. The band gaps, affected by both lattice constriction and octahedral tilting, show opposite trends in Pb-rich or Sn-rich perovskites with the increase of Cs for fixed Sn compositions. The Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb 0.25 Sn 0.75 (I 0.83 Br 0.17 ) 3 PVSCs achieve a power conversion efficiency (PCE) of 11.05%, a record for any PVSC containing 75% Sn perovskites, and the Cs 0.10 (MA 0.17 FA 0.83 ) 0.90 Pb 0.75 Sn 0.25 (I 0.83 Br 0.17 ) 3 PVSCs reach a record PCE of 15.78%. Moreover, the triple cation and double halide alloyed Pb–Sn perovskites exhibit improved device stability under inert and ambient conditions. This study, which illustrates the impact of cation and halide tuning on alloyed Pb–Sn perovskites, can be used to further eliminate Pb and improve device performance of high Sn PVSCs and other optoelectronic devices.more » « less
-
We present a combined experimental and density functional theory study that characterizes the charge and spin density in NiX2(3,5-lutidine)4(X= Cl, Br and I). In this material, magnetic exchange interactions occur via Ni2+–halide...halide–Ni2+pathways, forming one-dimensional chains. We find evidence for weak halide...halide covalency in the iodine system, which is greatly reduced whenX= Br and is absent forX= Cl; this is consistent with the reported `switching-on' of magnetic exchange in the larger-halide cases. Our results are benchmarked against density functional theory calculations on [NiHF2(pyrazine)2]SbF6, in which the primary magnetic exchange is mediated by F–H–F bridging ligands. This comparison indicates that, despite the largely depleted charge density found at the centre of halide...halide bonds, these through-space interactions can support strong magnetic exchange gated by weak covalency and enhanced by significant electron density overlapping that of the transition metal centres.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1126/sciadv.abb9379
