Journal
NATURE MATERIALS
Volume 12, Issue 7, Pages 641-646Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NMAT3629
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Funding
- French Ministere de l'Enseignement Superieur et de la Recherche
- French Agence Nationale de la Recherche (ANR) through project NOMILOPS
- French Agence Nationale de la Recherche (ANR) through project MULTIDOLLS
- Russian Foundation for Basic Research
- NSF
- DOE
- ARO
- ONR
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1066158] Funding Source: National Science Foundation
- EPSCoR
- Office Of The Director [0918970] Funding Source: National Science Foundation
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Multiferroics are compounds that show ferroelectricity and magnetism. BiFeO3, by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. Although this flurry of properties makes BiFeO3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property-antiferromagnetism-has not been investigated extensively, especially in thin films. Here we bring insight into the rich spin physics of BiFeO3 in a detailed study of the static and dynamic magnetic response of strain-engineered films. Using Mossbauer and Raman spectroscopies combined with Landau-Ginzburg theory and effective Hamiltonian calculations, we show that the bulk-like cycloidal spin modulation that exists at low compressive strain is driven towards pseudo-collinear antiferromagnetism at high strain, both tensile and compressive. For moderate tensile strain we also predict and observe indications of a new cycloid. Accordingly, we find that the magnonic response is entirely modified, with low-energy magnon modes being suppressed as strain increases. Finally, we reveal that strain progressively drives the average spin angle from in-plane to out-of-plane, a property we use to tune the exchange bias and giant-magnetoresistive response of spin valves.
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