Browsing by Author "Ramash, V"

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    Stability and scaling behavior of the spin cycloid in BiFeO3 thin films
    (Australian Institute of Physics, 2018-01-30) Burns, SR; Sando, D; Bertinshaw, J; Russell, L; Xu, X; Maran, R; Callori, SJ; Ramash, V; Cheung, J; Danilkin, SA; Deng, G; Lee, WT; Hu, S; Bellaiche, L; Seidel, J; Valanoor, N; Ulrich, C
    Multiferroic materials demonstrate excellent potential for next-generation multifunctional devices, as they exhibit coexisting ferroelectric and magnetic orders. Bismuth ferrite (BiFeO3) is a rare exemption where both order parameters exist far beyond room temperature, making it the ideal candidate for technological applications. To realize magnonic devices, a robust longrange spin cycloid with well-known direction is desired, since it is a prerequisite for the magnetoelectric coupling. Despite extensive investigation, the stabilization of a large-scale uniform spin cycloid in nanoscale (<300 nm) thin BiFeO3 films has not been accomplished. Using neutron diffraction we were able to demonstrate cycloidal spin order in 100 nm BiFeO3 thin films which became stable through the careful choice of crystallographic orientation and control of the electrostatic and strain boundary conditions during growth [1]. Furthermore, Co-doping, which has demonstrated to further stabilize the spin cycloid, did allow us to obtain spin cycloid order in films of just 50 nm thickness, i.e. films thinner than the cycloidal length of about 64 nm. Interestingly, in thin films the propagation direction of the spin cycloid has changed and shows a peculiar scaling behavior for thinnest films. We were able to support these observations by Monte Carlo theory based on a first-principles effective Hamiltonian method. Our results therefore offer new avenues for fundamental research and technical applications that exploit the spin cycloid in spintronic or magnonic devices.