Emergent electric field control of phase transformation in oxide superlattices

Abstract

Electric fields can transform materials with respect to their structure and properties, enabling various applications ranging from batteries to spintronics. Recently electrolytic gating, which can generate large electric fields and voltage-driven ion transfer, has been identified as a powerful means to achieve electric-field-controlled phase transformations. The class of transition metal oxides (TMOs) provide many potential candidates that present a strong response under electrolytic gating. However, very few show a reversible structural transformation at roomtemperature. Here, we report the realization of a digitally synthesized TMO that shows a reversible, electric-field-controlled transformation between distinct crystalline phases at room-temperature. In superlattices comprised of alternating one-unit-cell of SrIrO 3 and La 0.2 Sr 0.8 MnO 3 , we find a reversible phase transformation with a 7% lattice change and dramatic modulation in chemical, electronic, magnetic and optical properties, mediated by the reversible transfer of oxygen and hydrogen ions. Strikingly, this phase transformation is absent in the constituent oxides, solid solutions and larger period superlattices. Our findings open up a new class of materials for voltagecontrolled functionality.

Defects in complex oxide thin films for electronics and energy applications: challenges and opportunities

“…275 Similar reversible phase transformations mediated by hydrogen and oxygen ions was also observed in VO 2 , ZnO, WO 3 , SrRuO 3 , La 1Àx Sr x MnO 3 , La 0.7 Sr 0.3 MnO 3 /SrIrO 3 superlattice films, etc. 18,164,[276][277][278][279][280][281] Water was also used as a gating medium for achieving hydrogen doping. 282 The ionization of water to form H + and OH À occurs when a bias voltage over 1.23 V is applied between an electrode and TMOs in water.…”

Voltage‐Controlled Deblocking of Magnetization Reversal in Thin Films by Tunable Domain Wall Interactions and Pinning Sites

“…[26] There is growing recognition that voltageinduced changes in valency and phase, inherent to magnetoionic effects, can be applied to the magnetic layer beyond the interface. [13,17] For instance, voltagecontrol of magnetization up to ON/OFF switching of magnetism is possible in transition metal oxide (TMO) [13,27] and hybrid TMO/metal films [28][29][30] because of the switching between different chemical states induced by oxygen, hydrogen, or lithiumion transport. In some cobaltbased oxides, due to high ionic diffusion coefficients, control of stoichiometry and phase transformations by reversible ionic mechanisms are achieved both at interfaces and beyond the ultrathin limit.…”

“…[ 2–4 ] Voltage‐induced capacitive charging of a ferromagnetic metal interface causes volatile changes in the surface electronic band structure that affect the intrinsic magnetic properties in just a few atomic layers. [ 5–10 ] In contrast, magneto‐ionic mechanisms involve voltage‐induced ion migration and electrochemical reactions, [ 2,3,11–13 ] and can therefore induce very large and nonvolatile magnetic property changes. [ 12,14–18 ] As a result, magneto‐ionic materials have emerged as prominent energy‐efficient candidates for voltage‐programmable materials with potential applications in neuromorphic computing, domain‐wall logic, magnetic random access memory, and magnet‐based lab‐on‐a‐chip technologies.…”

Manipulation of the Electronic State of Mott Iridate Superlattice through Protonation Induced Electron‐Filling

“…It is important to note that the previous ILG studies on Sr 2 IrO 4 show only negligible modulation effect, [22] and the sample is easily damaged during ILG and therefore not appropriate for our proposed protonation study. Instead, we find that the SrTiO 3 /SrIrO 3 SL, which also has the 2D Ir-O layer as the key building block but with a much simpler crystalline and magnetic structure as compared with Sr 2 IrO 4 , [7][8][9]34,35] and more importantly the SL structure is very robust against the ILG as revealed recently in LSMO/SIO SL, [30] which makes this study practical. In the SL, the insulating SrTiO 3 layer forms a robust crystalline framework to stabilize the quasi-2D nature of Ir-O layers, [34] in which the J eff = 1/2 pseudospins are antiferromagnetically ordered and have the same translational symmetry along the c-axis as C-type AFM structure.…”

“…In this method, the proton, as the smallest ion in nature, is generated from the electrolyzed H 2 O within ionic liquid, which can be intercalated into samples with the application of electric-field. [25] Due to the principle of charge neutrality, the positively charged proton would be associated with one electron to complete the structural transformation as protonation (Figure 1b,c), which can lead to the modulation of pronounced bulk electron doping with emergence of exotic electronic states within a series of complex oxide systems [25][26][27][28][29][30][31][32] and even in iron-based superconductors. [33] We note that such approach forms an important strategy to manipulate electron doping to complement the well-established chemical substation, oxygen vacancy formation as well as alkali-metal intercalation in complex oxide systems.…”