Browsing by Author "Martin, Lane W."
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Effect of fabrication processes on BaTiO3 capacitor properties(AIP Publishing, 2024) Jiang, Yizhe; Tian, Zishen; Kavle, Pravin; Pan, Hao; Martin, Lane W.; Rice Advanced Materials InstituteThere is an increasing desire to utilize complex functional electronic materials such as ferroelectrics in next-generation microelectronics. As new materials are considered or introduced in this capacity, an understanding of how we can process these materials into those devices must be developed. Here, the effect of different fabrication processes on the ferroelectric and related properties of prototypical metal oxide (SrRuO3)/ferroelectric (BaTiO3)/metal oxide (SrRuO3) heterostructures is explored. Two different types of etching processes are studied, namely, wet etching of the top SrRuO3 using a NaIO4 solution and dry etching using an Ar+-ion beam (i.e., ion milling). Polarization-electric-field hysteresis loops for capacitors produced using both methods are compared. For the ion-milling process, it is found that the Ar+ beam can introduce defects into the SrRuO3/BaTiO3/SrRuO3 devices and that the milling depth strongly influences the defect level and can induce a voltage imprint on the function. Realizing that such processing approaches may be necessary, work is performed to ameliorate the imprint of the hysteresis loops via ex situ “healing” of the process-induced defects by annealing the ferroelectric material in a barium-and-oxygen-rich environment via a chemical-vapor-deposition-style process. This work provides a pathway for the nanoscale fabrication of these candidate materials for next-generation memory and logic applications.Item Emergent chirality in a polar meron to skyrmion phase transition(Springer Nature, 2023) Shao, Yu-Tsun; Das, Sujit; Hong, Zijian; Xu, Ruijuan; Chandrika, Swathi; Gómez-Ortiz, Fernando; García-Fernández, Pablo; Chen, Long-Qing; Hwang, Harold Y.; Junquera, Javier; Martin, Lane W.; Ramesh, Ramamoorthy; Muller, David A.Polar skyrmions are predicted to emerge from the interplay of elastic, electrostatic and gradient energies, in contrast to the key role of the anti-symmetric Dzyalozhinskii-Moriya interaction in magnetic skyrmions. Here, we explore the reversible transition from a skyrmion state (topological charge of −1) to a two-dimensional, tetratic lattice of merons (with topological charge of −1/2) upon varying the temperature and elastic boundary conditions in [(PbTiO3)16/(SrTiO3)16]8 membranes. This topological phase transition is accompanied by a change in chirality, from zero-net chirality (in meronic phase) to net-handedness (in skyrmionic phase). We show how scanning electron diffraction provides a robust measure of the local polarization simultaneously with the strain state at sub-nm resolution, while also directly mapping the chirality of each skyrmion. Using this, we demonstrate strain as a crucial order parameter to drive isotropic-to-anisotropic structural transitions of chiral polar skyrmions to non-chiral merons, validated with X-ray reciprocal space mapping and phase-field simulations.Item Size-Induced Ferroelectricity in Antiferroelectric Oxide Membranes(Wiley, 2023) Xu, Ruijuan; Crust, Kevin J.; Harbola, Varun; Arras, Rémi; Patel, Kinnary Y.; Prosandeev, Sergey; Cao, Hui; Shao, Yu-Tsun; Behera, Piush; Caretta, Lucas; Kim, Woo Jin; Khandelwal, Aarushi; Acharya, Megha; Wang, Melody M.; Liu, Yin; Barnard, Edward S.; Raja, Archana; Martin, Lane W.; Gu, X. Wendy; Zhou, Hua; Ramesh, Ramamoorthy; Muller, David A.; Bellaiche, Laurent; Hwang, Harold Y.Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve in antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing antiferroelectrics for high-energy-density storage applications, understanding their size effects will provide key information for optimizing device performances at small scales. Here, the fundamental intrinsic size dependence of antiferroelectricity in lead-free NaNbO3 membranes is investigated. Via a wide range of experimental and theoretical approaches, an intriguing antiferroelectric-to-ferroelectric transition upon reducing membrane thickness is probed. This size effect leads to a ferroelectric single-phase below 40 nm, as well as a mixed-phase state with ferroelectric and antiferroelectric orders coexisting above this critical thickness. Furthermore, it is shown that the antiferroelectric and ferroelectric orders are electrically switchable. First-principle calculations further reveal that the observed transition is driven by the structural distortion arising from the membrane surface. This work provides direct experimental evidence for intrinsic size-driven scaling in antiferroelectrics and demonstrates enormous potential of utilizing size effects to drive emergent properties in environmentally benign lead-free oxides with the membrane platform.Item Switching the spin cycloid in BiFeO3 with an electric field(Springer Nature, 2024) Meisenheimer, Peter; Moore, Guy; Zhou, Shiyu; Zhang, Hongrui; Huang, Xiaoxi; Husain, Sajid; Chen, Xianzhe; Martin, Lane W.; Persson, Kristin A.; Griffin, Sinéad; Caretta, Lucas; Stevenson, Paul; Ramesh, Ramamoorthy; Rice Advanced Materials InstituteBismuth ferrite (BiFeO3) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements. Using nitrogen vacancy-based diamond magnetometry, we observe the magnetic spin cycloid structure of BiFeO3 in real space. This structure is magnetoelectrically coupled through symmetry to the ferroelectric polarization and this relationship is maintained through electric field switching. Through a combination of in-plane and out-of-plane electrical switching, coupled with ab initio studies, we have discovered that the epitaxy from the substrate imposes a magnetoelastic anisotropy on the spin cycloid, which establishes preferred cycloid propagation directions. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the spin spiral propagation vector to changes to specific switching events.