Strain and Magnetic Field Induced Spin‐Structure Transitions in Multiferroic BiFeO3

reduced from the bulk value. Neutron diffraction data support this hypothesis, with a cycloid period larger than the bulk value and increasing with strain and/or magnetic field. Analysis of the data in light of Landau–Lifshitz (LL) calculations [7] indicates that very small strains are sufficient to induce large modifications in magnetoelastic coupling, [8] suggesting interesting opportunities for strain-and/or field-mediated devices which take advantage of finite-size effects in multiferroic films. Frustration in magnetic systems with interplay between spin and charge often brings about non-collinear orders such as spin spirals and cycloids. [9] These configurations can arise either directly from competing exchange interactions, as is the case for the spiral order in TbMnO 3 , [10] or through the influence In multiferroic materials, [1] the coexistence of several exchange interactions often results in competition between non-collinear spin orders which are sensitive to temperature, hydrostatic pressure , or magnetic field. In bismuth ferrite (BiFeO 3), a room-temperature multiferroic, [2] the intricacy of the magnetic phase diagram is only fully revealed in thin films: [3] epitaxial strain suppresses the cycloidal spin order present in the bulk, [4] transforming it into various antiferromagnetic states, modifying the spin direction and ordering patterns. [5] Here, we explore the combined effect of strain and magnetic field on the spin order in BiFeO 3. Through nuclear resonant scattering (NRS) [6] and Raman spectroscopy, we show that both strain and magnetic field destabilize the cycloid, resulting in a critical field sharply