Anharmonic phonons and magnons in BiFeO3

Abstract

The phonon density of states (DOS) and magnetic excitation spectrum of polycrystalline BiFeO3 were measured for temperatures 200 ≤ T ≤ 750 K , using inelastic neutron scattering (INS). Our results indicate that the magnetic spectrum of BiFeO3 closely resembles that of similar Fe perovskites, such as LaFeO3, despite the cycloid modulation in BiFeO3. We do not find any evidence for a spin gap. A strong T -dependence of the phonon DOS was found, with a marked broadening of the whole spectrum, providing evidence of strong anharmonicity. This anharmonicity is corroborated by large-amplitude motions of Bi and O ions observed with neutron diffraction. A clear anomaly is seen in the T dependence of Bi-dominated modes across the Néel transition. These results highlight the importance of spin-phonon coupling in this material.

Structure and lattice dynamics of solid solutions (1 − x)BiFeO3-xANbO3 (A = K, Na)

“…The Raman spectrum of the BiFeO 3 ceramics shown in the lower panel of Fig. 3 agrees with the results of [11][12][13][14][15][16][17][18][19][20]. The origin of the vibrational spectrum of BiFeO 3 in the transition from the cubic praphase to rhombohedral R3c structure was described in [21].…”

Neutron inelastic scattering measurements of low-energy phonons in the multiferroicBiFeO3

“…14 A full understanding of the energy-momentum dependence of the dynamics in BiFeO 3 is, however, still far from complete. Only with the recent achievements in the growth of large BiFeO 3 single crystals have researchers been able to start carrying out neutron inelastic and x-ray scattering measurements on both the lattice and spin dynamics [15][16][17][18][19] . In this paper we present neutron inelastic scattering measurements of the low-energy phonon modes in a large BiFeO 3 single crystal from 300 K to 700 K. , and the lowest-lying optic modes are mapped out in three different Brillouin zones.…”

Spin and lattice excitations of aBiFeO3thin film and ceramics

“…23,24 Furthermore, the influence of strain on the number of spin excitations and their frequencies were reported for epitaxial thin films grown on a series of substrates. 25 Time-domain THz spectroscopy, 26 inelastic neutron scattering measurements [27][28][29][30] and absorbance spectroscopy in the THz range 31 have revealed modes similar to the Raman-active onespredicted by theoretical calculations. [31][32][33][34][35] The best agreement between the experimental and theoretical spin-excitation frequencies (including their splitting in external magnetic field) was obtained for a microscopic model that takes into ac-count the nearest and next-nearest neighbor exchange interactions, two Dzyaloshinskii-Moriya interactions and an easy-axis anisotropy.…”