Magnon sidebands and spin-charge coupling in bismuth ferrite probed by nonlinear optical spectroscopy

Abstract

The interplay between spin waves ͑magnons͒ and electronic structure in materials leads to the creation of additional bands associated with electronic energy levels which are called magnon sidebands. The large difference in the energy scales between magnons ͑meV͒ and electronic levels ͑eV͒ makes this direct interaction weak and hence makes magnon sidebands difficult to probe. Linear light absorption and scattering techniques at low temperatures are traditionally used to probe these sidebands. Here we show that optical secondharmonic generation, as the lowest-order nonlinear process, can successfully probe the magnon sidebands at room temperature and up to 723 K in bismuth ferrite, associated with large wave vector multimagnon excitations which linear absorption studies are able to resolve only under high magnetic fields and low temperatures. Polarized light studies and temperature dependence of these sidebands reveal a spin-charge coupling interaction of the type P s L 2 between the spontaneous polarization ͑P s ͒ and antiferromagnetic order parameter, L in bismuth ferrite, that persists with short-range correlation well into the paramagnetic phase up to high temperatures. These observations suggest a broader opportunity to probe the collective spin-charge-lattice interactions in a wide range of material systems at high temperatures and electronic energy scales using nonlinear optics.

IR absorption and linear dichroism in BiFe0.5Co0.5O3 films

“…3, the position of the low-energy bands in the optical density spectra D(hx) of BiFe 0.5-Co 0.5 O 3 is close to the position of the Raman peaks observed in BiFeO 3 [20,21]. Figure 4 shows the temperature dependence of transmission t(T) at hx = 0.155 eV of F230 film.…”

“…Authors of Ref. [20] also have revealed the bands at hx = 0.156 eV (1260 cm -1 ), 0.192 eV (1550 cm -1 ), and 0.299 eV (2415 cm -1 ) in the IR absorption spectra and in the Raman ones of BiFeO 3 . These bands were associated with two-phonon process, two-mangon and three-magnon excitations, respectively.…”

“…There are papers devoted to the optical properties of undoped BiFeO 3 and BiFe 1-x Co x O 3 films with different concentration of Co ions [17][18][19][20][21][22][23][24][25]. As a rule, the optical properties are studied in far infrared (IR) range or in the fundamental absorption range.…”

Electronic Band Structures and Phase Transitions of Ferroelectric and Multiferroic Oxides

“…Based on the theoretical calculations and experimental observations, the four energy bands can be uniquely assigned to the following electronic transitions: (1) [51][52][53][54][55] Within the experimental error bars, the energy positions shift toward the higher energy at the temperature of 5.3 K except for the second excitation, which can be attributed to the energy band variations. Nevertheless, the origin of the abnormal shift for the second excitation is unclear in the present work.…”

Multi-stimuli manipulation of antiferromagnetic domains assessed by second-harmonic imaging

“…4d), it is clear that even if some similarities remain, the AF pattern has mostly been re-initialized. More interestingly, one could expect that even sub-coercive electric fields should affect the AF texture through a term in E · L 2 in the free energy 21 . Other terms in E i L j M k (with i, j, k the space directions) couple to the uncompensated moment M of strained BFO (ref.…”