Modulating Magnetism in Ferroelectric Polymer-Gated Perovskite Manganite Films with Moderate Gate Pulse Chains

Abstract

Most previous attempts on achieving electric-field manipulation of ferromagnetism in complex oxides, such as La0.66Sr0.33MnO3 (LSMO), are based on electrostatically induced charge carrier changes through high-k dielectrics or ferroelectrics. Here, the use of a ferroelectric copolymer, polyvinylidene fluoride with trifluoroethylene [P­(VDF-TrFE)], as a gate dielectric to successfully modulate the ferromagnetism of the LSMO thin film in a field-effect device geometry is demonstrated. Specifically, through the application of low-voltage pulse chains inadequate to switch the electric dipoles of the copolymer, enhanced tunability of the oxide magnetic response is obtained, compared to that induced by ferroelectric polarization. Such observations have been attributed to electric field-induced oxygen vacancy accumulation/depletion in the LSMO layer upon the application of pulse chains, which is supported by surface-sensitive-characterization techniques, including X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism. These techniques not only unveil the electrochemical nature of the mechanism but also establish a direct correlation between the oxygen vacancies created and subsequent changes to the valence states of Mn ions in LSMO. These demonstrations based on the pulsing strategy can be a viable route equally applicable to other functional oxides for the construction of electric field-controlled magnetic devices.

Modulating Antiferromagnetic La0.35Sr0.65 MnO3 via Low-Voltage Pulsing Across a Ferroelectric Copolymer Gate Dielectric

“…While our goal is to modulate the magnetic property of AF-LSMO thin film, any change in the bottom FM-LSMO layer may complicate the interpretation of results. We have previously demonstrated that pulse modulation of FM-LSMO [31,32] can alter its resistance, MR value at high field and Curie temperature (T C ). The RT curves of pristine state, stage I and stage II are shown in Fig.…”

“…Epitaxial AF-LSMO and FM-LSMO thin films were grown on TiO 2 -terminated SrTiO 3 (001) (STO) substrates by pulsed laser deposition (PLD), using excimer KrF laser (wavelength 248 nm) to ablate the corresponding ceramic targets at a frequency of 1 Hz; TiO 2 -terminated STO substrates were prepared through leaching in boiling deionized (DI) water and thermal annealing processes [31], [32]. FM-LSMO layers were deposited in an oxygen pressure of 150 mTorr and substrate temperature of 700⁰ C, which were then postannealed at 10 Torr oxygen for 5 minutes at the same temperature.…”

“…Here, we deploy P(VDF-TrFE) as the top gate dielectric for nonvolatile control of electrical and magnetic properties of epitaxial antiferromagnetic La 0.35 Sr 0.65 MnO 3 (AF-LSMO) thin films. A low-voltage pulsing scheme was used to control the physical properties of AF-LSMO thin films, by applying pulses with voltage lower than ferroelectric switching threshold [31], [32]. In such a manner, the electrical breakdown of the dielectric layer can be suppressed.…”