Magnetic phenomena from the confines of a nonmagnetic material
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worry about lattice matching at the unit cell,” comments Dave Johnson, an expert in misfit layer heterostructures at the University of Oregon. “The synthesis of heterostructures via vdW epitaxy, or other approaches, will change the way we think about materials optimization and enable the design of materials by actually modifying the identity, sequence, and nanoarchitecture of the heterostructured solid so that you can selectively tune device performance.” This epitaxial growth protocol is not only limited to 2D semiconductors, but
is predicted to also be accessible to both 2D metals and insulators. Despite this promise, the challenge will lie in tuning the growth temperature and pressure for each individual material in order to address problems with interfacial contamination, diffusion, and evaporation. If these conditions can be met, the synthesis of vdW misfit heterostructures will unlock a realm of materials that have not yet been explored, and will allow the selective tuning of materials’ properties based on its epitaxial building blocks. Tyler W. Farnsworth
nickelates are both electrically insulating and antiferromagnetic. However, Magnetic phenomena from LNO is known to be both metallic the confines of a nonmagnetic material and nonmagnetic at all temperatures. Researchers have shown that growing here have been many recent advancthin epitaxial LNO films in the [111] dies in the synthesis, manipulation, and rection in between layers of LMO can study of complex atomic-scale structures promote a dimensionality-induced insuand interfaces. Among these, understandlating character as well as antiferromaging the fundamental changes in physical netic ordering of the magnetic moments. properties in areas of reduced dimensionAs Gibert describes it, “LNO in these ality has played an important role and has specific conditions behaves more like led to improvements in spintronics, digiall the other nickelates.” Furthermore, tal memory, and transistor technologies. by restricting the LNO layer to only 7 A study from the University of Geneva, monolayers (ML), they were able to promote a number of complex temperature-dependent exchange coupling phenomena. In a layer this thin, the LNO monolayers were found to couple antiferromagnetically to each other creating a 4-unitcell stack that equates to a net zero magnetic moment, just like the rest of the perovskite nickelates. However, if only 7 ML of LNO are sandwiched between the LMO layers, the 4-unit-cell sequence is unfinished and the magnetic moments at the ends of the LNO layer (at the interfaces) are pointing in opposite directions; see Figure. Since the LMO layer couples ferromagnetically (parallel) to the LNO layer by Model of the magnetic arrangement of 7-monolayer LaNiO3 in the LaNiO3/LaMnO3 superlattice. The exchange a charge-transfer mechanism, bias sign reversal is exclusively observed for the superlattice with 7-monolayer LNO (blue), that is, not for successive LMO layers are then 5-monolayer LNO or 8-monolayer LNO. Credit: Nature Communications.
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Switzerland, publ
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