Electric-Field Control of Oxygen Vacancies and Magnetic Phase Transition in a Cobaltite/Manganite Bilayer

Abstract

Manipulation of oxygen vacancies (V O ) in single oxide layers by varying the electric field can result in significant modulation of the ground state. However, in many oxide multilayers with strong application potentials, e.g. ferroelectric tunnel junctions and solid-oxide fuel cells, understanding V O behaviour in various layers under an applied electric field remains a challenge, owing to complex V O transport between different layers. By sweeping the external voltage, a reversible manipulation of V O and a corresponding fixed magnetic phase transition sequence in cobaltite/manganite (SrCoO 3-x /La 0.45 Sr 0.55 MnO 3-y ) heterostructures are reported. *The magnetic phase transition sequence confirms that the priority of electric-field-induced V O formation/annihilation in the complex bilayer system is mainly determined by the V O formation energies and Gibbs free energy differences, which is supported by theoretical analysis. We not only realize a reversible manipulation of the magnetic phase transition in an oxide bilayer, but also provide insight into the electric field control of V O engineering in heterostructures.

Doping- and Strain-Dependent Electrolyte-Gate-Induced Perovskite to Brownmillerite Transformation in Epitaxial La1–xSrxCoO3−δ Films

“…As gating proceeds, proliferation of V O through the film is required, rendering D V O important. 1,[11][12][13][14][15][16][17][18][19][20]22,28,29,33,34 Experimental data on this in P LSCO (from electrochemical chronoamperometry 59−62 ) are shown in Figure 7d. As noted previously 22 and as is likely at the root of the extensive recent literature focus on electrochemical gating of cobaltites, 1,[11][12][13][14][15][16][17][18][19][20]22,28,29,33,34 D V O in LSCO is exceptionally high, 23 to the degree that even at 300 K, the V O diffusion length, l d = (D V O t) 1/2 , on the 30 min time scales here, is substantial.…”

“…1,[11][12][13][14][15][16][17][18][19][20]22,28,29,33,34 Experimental data on this in P LSCO (from electrochemical chronoamperometry 59−62 ) are shown in Figure 7d. As noted previously 22 and as is likely at the root of the extensive recent literature focus on electrochemical gating of cobaltites, 1,[11][12][13][14][15][16][17][18][19][20]22,28,29,33,34 D V O in LSCO is exceptionally high, 23 to the degree that even at 300 K, the V O diffusion length, l d = (D V O t) 1/2 , on the 30 min time scales here, is substantial. As illustrated by the blue points and the dashed vertical line in Figure 7d, the data of Mefford et al, 59 for example, suggest several-hundred-nm V O diffusion lengths under our gating conditions, significantly larger than the film thickness (28 u.c.…”

“…1,11−20 This forms by ordering V O in lines along [101] directions, in alternate (100) planes, quadrupling the caxis lattice parameter, and creating both octahedral and tetrahedral Co sites (Figure 1a). 1,[11][12][13][14][15][16][17][18][19][20]24,25 The resultant phase has a very different electronic structure to P LSCO, exhibiting a clear energy gap, and insulating antiferromagnetism with a Neél temperature of 570 K. 1,[11][12][13][14][15][16][17][18][19][20]26,27 The electronic, magnetic, and optical properties of the SrCoO 3−δ system can thus be massively modulated via topotactic transformation between P and BM and between an F metal and an antiferromagnetic (AF) insulator. 1,11−20 Building on demonstrations of thermal cycling between the SCO P and BM, 15,20 and related phenomena via gettering with a reactive overlayer, 28,29 reversible voltage-driven BM ↔ P transformations have recently been established in several studies.…”

Voltage Control of Magnetism above Room Temperature in Epitaxial SrCo1–xFexO3−δ

“…Voltage-driven migration of ions in magnetic materials, that is, the magneto-ionic effect, has become an emerging strategy for controlling magnetic properties. − Utilizing the redox reaction at the interface of an ultrathin metal or alloy layer adjacent to gate oxides enables a tuning of the magnetic anisotropy, − coercivity, , and exchange bias in different systems. An example is provided by O 2– -driven easy axis reorientation of a Co/GdO x heterostructure whose typical response time is of the order of minutes. , However, this approach is usually limited to metal layer thicknesses of order 1 nm and requires elevated temperatures (>100 °C).…”

“…In order to accomplish a more robust magnetic response, processes that involve volumetric magnetic phase transitions induced by voltage-driven ion migration have drawn considerable interest. − Like lithium ions , that can alter the magnetic properties of bulk-like electrodes ( e.g ., Fe 2 O 3 ) upon charging and discharging in a battery, oxygen − and hydrogen , ions are also capable of inducing magnetic phase transitions in certain oxides. Compared with polycrystalline oxide films ( e.g ., Co 3 O 4 ), in which the response is slow even with high voltages, epitaxial complex oxides are of greater interest.…”