Tunable Magnetic Nanostructures: Property Characterization and Modeling
Zusammenfassung der Projektergebnisse
The principal idea pursued in the project is that the electric field-effect can be used to control dynamically and reversibly magnetic properties of conducting materials. The idea stemmed from the observation that properties of materials can be modified using two different approaches. In the first case the materials are tailored for certain properties by varying their composition and (micro) structure. These tailored properties are fixed to the structural and chemical features of the material and by their very nature are irreversible. One of the ways to circumvent this limitation is change of the charge carrier concentration via applied electric field, thus introducing an element of tunability to the control of material properties. It was proposed that the generation of surface charge upon the application of an electric field can lead to significant changes in the magnetic properties even of highly conducting systems by judiciously exploiting the high surface-to-volume ratios that are typical of nanostructures. To enhance material susceptibility to surface charging the studies were concentrated on metallic systems with inherent competition of two or more electronic-magnetic phases, i.e., magnetic conducting oxides La1-xSrxMnO3 (LSMO) and FeRh alloys. With such a choice, it was anticipated that the system of interest would be adjusted near a critical point, where small changes in carrier concentration are sufficient to induce a phase transition. Accordingly, a variety of nanostructures (epitaxial thin films, heterostructures, nanoporous structures) were synthesized, characterized and their magnetic properties studied as function of material chemistry and microstructural features. In the course of the project an unconventional sputtering technique – the Large-Distance Magnetron Sputtering (LDMS) method – was established, which enabled epitaxial deposition of the heterostructures with highest crystallinity and markedly smooth interfaces, necessary for effective field-effect control of magnetism. In the next step, to bring about a surface charge modulation at the magnetic material surface two different ways were successfully explored (i) electrolyte charging and (ii) ferroelectric charging. Consequently, a fully reversible control of the magnetic state through an electric field modulation of the carrier concentration was achieved in strongly correlated La1-xSrxMnO3 and FeRh alloys. The exceptional quality of the LSMO/ferroelectric devices enabled, for a first time, in-situ (in SQUID magnetometer) magnetization modulation upon surface charging in the entire range of relevant temperatures and magnetic fields. The quantitative results of these experiments eventually allowed for developing of a physical picture of a magneto-electric coupling at the LSMO/ferroelectric interface based on the electronic phase separation of competing antiferromagnetic and ferromagnetic phases.
Projektbezogene Publikationen (Auswahl)
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“Room temperature reversible tuning of magnetism of electrolyte-gated La0.75Sr0.25MnO3 nanoparticles”, Journal of Applied Physics, 113, 3, 033913 – 033913-7 (2010)
A.K. Mishra, A.J. Darbandi, P.M. Leufke, R. Kruk and H. Hahn
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“Ferroelectric vs. structural properties of large-distance sputtered epitaxial LSMO/PZT heterostructures”, AIP Advances 2, 032184 (2012)
P.M. Leufke, R. Kruk, D. Wang, C. Kübel, and H. Hahn
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“Large-distance rf- and dc-sputtering of epitaxial La1−xSrxMnO3 thin film”, Thin Solid Films 520, 5521 (2012)
P.M. Leufke, A.K. Mishra, A. Beck, D. Wang, C. Kübel, R. Kruk, and H. Hahn
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“Evidence for enhanced ferromagnetism in an iron-based nanoglass”, Applied Physics Letters 103, 073106 (2013)
R. Witte, T. Feng, J. Fang, A. Fischer, M. Ghafari, R. Kruk, R.A. Brand, H. Gleiter and H. Hahn
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“In situ magnetometry studies of magnetoelectric LSMO/PZT heterostructures”, Physical Review 87, 094416 (2013)
P.M. Leufke, R. Kruk, R.A. Brand and H. Hahn
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“Intercalation-driven reversible control of magnetism in bulk ferromagnets”, Adv. Mater. 2014, 26, 4639–4644
S. Dasgupta, B. Das, M. Knapp, R. A. Brand, H. Ehrenberg , R. Kruk and H. Hahn
