Electrostatic versus Electrochemical Doping and Control of Ferromagnetism in Ion-Gel-Gated Ultrathin La0.5Sr0.5CoO3-δ

Jeff Walter, Helin Wang, Bing Luo, C. Daniel Frisbie, Chris Leighton

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

Recently, electrolyte gating techniques employing ionic liquids/gels in electric double layer transistors have proven remarkably effective in tuning charge carrier density in a variety of materials. The ability to control surface carrier densities at levels above 1014 cm-2 has led to widespread use in the study of superconductivity, insulator-metal transitions, etc. In many cases, controversy remains over the doping mechanism, however (i.e., electrostatic vs electrochemical (e.g., redox-based)), and the technique has been less applied to magnetic materials. Here, we discuss ion gel gating of nanoscale 8-unit-cell-thick hole-doped La0.5Sr0.5CoO3-δ (LSCO) films, probing in detail the critical bias windows and doping mechanisms. The LSCO films, which are under compressive stress on LaAlO3(001) substrates, are metallic and ferromagnetic (Curie temperature, TC ∼ 170 K), with strong anomalous Hall effect and perpendicular magnetic anisotropy. Transport measurements reveal that negative gate biases lead to reversible hole accumulation (i.e., predominantly electrostatic operation) up to some threshold, whereas positive bias immediately induces irreversibility. Experiments in inert/O2 atmospheres directly implicate oxygen vacancies in this irreversibility, supported by atomic force microscopy and X-ray photoelectron spectroscopy. The results are thus of general importance, suggesting that hole- and electron-doped oxides may respond very differently to electrolyte gating. Reversible voltage control of electronic/magnetic properties is then demonstrated under hole accumulation, including resistivity, magnetoresistance, and TC. The sizable anomalous Hall coefficient and perpendicular anisotropy in LSCO provide a particularly powerful probe of magnetism, enabling direct extraction of the voltage-dependent order parameter and TC shift. The latter amounts to ∼7%, with potential for much stronger modulation at lower Sr doping.

Original languageEnglish (US)
Pages (from-to)7799-7810
Number of pages12
JournalACS Nano
Volume10
Issue number8
DOIs
StatePublished - Aug 23 2016

Fingerprint

Ferromagnetism
ferromagnetism
Electrostatics
Gels
Doping (additives)
gels
Ions
electrostatics
Electrolytes
Carrier concentration
Hall effect
Ionic Liquids
ions
Metal insulator transition
Control surfaces
Magnetic anisotropy
Magnetic materials
Magnetism
electrolytes
Magnetoresistance

Keywords

  • cobaltites
  • electrolyte gating
  • field-effect transistors
  • ion gels
  • perovskite oxides

How much support was provided by MRSEC?

  • Primary

Reporting period for MRSEC

  • Period 3

PubMed: MeSH publication types

  • Journal Article

Cite this

Electrostatic versus Electrochemical Doping and Control of Ferromagnetism in Ion-Gel-Gated Ultrathin La0.5Sr0.5CoO3-δ. / Walter, Jeff; Wang, Helin; Luo, Bing; Frisbie, C. Daniel; Leighton, Chris.

In: ACS Nano, Vol. 10, No. 8, 23.08.2016, p. 7799-7810.

Research output: Contribution to journalArticle

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abstract = "Recently, electrolyte gating techniques employing ionic liquids/gels in electric double layer transistors have proven remarkably effective in tuning charge carrier density in a variety of materials. The ability to control surface carrier densities at levels above 1014 cm-2 has led to widespread use in the study of superconductivity, insulator-metal transitions, etc. In many cases, controversy remains over the doping mechanism, however (i.e., electrostatic vs electrochemical (e.g., redox-based)), and the technique has been less applied to magnetic materials. Here, we discuss ion gel gating of nanoscale 8-unit-cell-thick hole-doped La0.5Sr0.5CoO3-δ (LSCO) films, probing in detail the critical bias windows and doping mechanisms. The LSCO films, which are under compressive stress on LaAlO3(001) substrates, are metallic and ferromagnetic (Curie temperature, TC ∼ 170 K), with strong anomalous Hall effect and perpendicular magnetic anisotropy. Transport measurements reveal that negative gate biases lead to reversible hole accumulation (i.e., predominantly electrostatic operation) up to some threshold, whereas positive bias immediately induces irreversibility. Experiments in inert/O2 atmospheres directly implicate oxygen vacancies in this irreversibility, supported by atomic force microscopy and X-ray photoelectron spectroscopy. The results are thus of general importance, suggesting that hole- and electron-doped oxides may respond very differently to electrolyte gating. Reversible voltage control of electronic/magnetic properties is then demonstrated under hole accumulation, including resistivity, magnetoresistance, and TC. The sizable anomalous Hall coefficient and perpendicular anisotropy in LSCO provide a particularly powerful probe of magnetism, enabling direct extraction of the voltage-dependent order parameter and TC shift. The latter amounts to ∼7{\%}, with potential for much stronger modulation at lower Sr doping.",
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