PGI Kolloquium: Prof. Dr. Chris Leighton, University of Minnesota, Minneapolis, USA

Online Talk

Please note: You will receive the link to the online talk in the e-mail invitation, usually sent out a few days before the lecture takes place. It is also available on request from the contact person below.

Ionically-Controlled Ferromagnetism

Abstract

Recently, incorporation of electrolytes (e.g., ionic liquids) into field-effect transistors has been shown to enable electric double layer transistors, which can induce large (10¹⁵ cm^-2) carrier densities at surfaces. These correspond to substantial fractions of an electron or hole per unit cell in most materials, sufficient to electrically control electronic phase transitions. While this has stimulated much interest, challenges remain, including understanding mechanisms (electrostatic vs. electrochemical [1]), developing operando characterization methods, and assessing the full power and universality of the approach.

Here, I review our work applying electrolyte gating using solid ion gels [1-6] to oxides and sulfides, focused on voltage-controlled magnetism. The latter is important, bearing potential for novel, low-power data storage and processing. Our findings greatly clarify electrostatic vs. electrochemical mechanisms, showing that electrostatic gating vs. oxygen vacancy creation/annihilation can be understood based on bias polarity, and the enthalpy of formation and diffusivity of oxygen vacancies [1-6].

Such understanding was developed from application of operando probes, particularly synchrotron X-ray diffraction [3] and absorption/dichroism [6], and polarized neutron reflectometry [3,5]. Electrical control of magnetism in perovskite La_1-xSr_xCoO_3-d is then demonstrated in both electrochemical [3] and electrostatic [2,4,5] modes, reversibly modulating Curie temperatures over >200 K windows. Most recently, this has been advanced beyond electrical modulation of ferromagnets, or electrical induction of ferromagnetism from antiferro- or para-magnetic states, demonstrating reversible voltage-induced ferromagnetism in a diamagnet, using FeS₂ as a model system [7]. 

[1] C. Leighton, Nat. Mater. 18, 13 (2019).

[2] J. Walter, H. Wang, B. Luo and C. Leighton, ACS Nano 10, 7799 (2016).

[3]

J. Walter, G. Yu, B. Yu, A. Grutter, B. Kirby, J. Borchers, Z. Zhang, H. Zhou, T. Birol, M. Greven, and C. Leighton, Phys. Rev. Materials 1, 071403(R) (2017).

[4]

P.P. Orth, R.M. Fernandes, J. Walter, C. Leighton and B.I. Shklovskii, Phys. Rev. Lett. 118, 106801 (2017).

[5] J. Walter, T. Charlton, H. Ambaye, M. Fitzsimmons, P. Orth, R. Fernandes, B. Shklovskii and C. Leighton,

Phys. Rev. Mater

ials 2, 111406(R) (2018)

[6]

B. Yu, G. Yu, J. Walter, V. Chaturvedi, J. Gotchnik, J. Freeland, C. Leighton and M. Greven, Appl. Phys. Lett. 116, 201905 (2020).

[7]

J. Walter, B. Voigt, E. Day-Roberts, T. Birol, R. Fernandes and C. Leighton, Sci. Adv. 6, eabb7721 (2020).

Kontakt

Oleg Petracic

Telefon: +49 2461 61-4519

Fax:  +49 2461 61-2610

E-Mail: o.petracic@fz-juelich.de