Abstract
Coherent magnons and acoustic phonons were impulsively excited and probed in thin films of the room temperature multiferroic Bi${}_{1\ensuremath{-}x\ensuremath{-}y}$Dy${}_{x}$La${}_{y}$FeO${}_{3}$ using femtosecond laser pulses. The elastic moduli of rhombohedral, tetragonal, and rare-earth doped BiFeO${}_{3}$ were determined from acoustic-mode frequencies in conjunction with spectroscopic ellipsometry. A weak ferromagnetic order, induced alternately by magnetization in the growth direction or by tetragonality, created a magnon oscillation at 75 GHz, indicative of a Dzyaloshinskii-Moriya interaction energy of 0.31 meV.
Highlights
In magnetoelectric multiferroics, the magnetization and electrical polarization are strongly coupled,[1,2,3,4] enabling potential applications in magnetic data storage and spintronic devices.[5]
The G-type antiferromagnetic (AFM) order on the 3d5 Fe3+ sites is disrupted by a weak ferromagnetic component
The Fe-O-Fe chain has no center of symmetry, resulting in the canting of adjacent spins via the Dzyaloshinskii-Moriya (DM) interaction.[13,14]
Summary
The magnetization and electrical polarization are strongly coupled,[1,2,3,4] enabling potential applications in magnetic data storage and spintronic devices.[5]. Ferroelectric and AFM orders originate from different ions, and the spin cycloid prohibits the linear ME effect in bulk BFO.[13] While the application of a large magnetic field (20 T) can suppress the cycloid and recover a linear ME effect,[16] epitaxial strain[2] and chemical doping[17,18] have been explored as routes to obtain stronger coupling at lower magnetic fields. The partial substitution of Bi on the perovskite A−site with lanthanides has been explored as a route to enhance the remnant polarization, saturation magnetization, and the coupling between the two orders. In this article a study of dynamic ME coupling in BFO thin films is reported, in particular the influence of tetragonality and of lanthanide substitution on the perovskite A−site.
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