Abstract
We report the magnetic-field dependence of the THz absorption and nonreciprocal directional dichroism spectra of BiFeO3 measured on the three principal crystal cuts for fields applied along the three principal directions of each cut. From the systematic study of the light polarization dependence, we deduced the optical selection rules of the spin-wave excitations. Our THz data, combined with small-angle neutron scattering results showed that (i) an in-plane magnetic field rotates the q vectors of the cycloids perpendicular to the magnetic field and (ii) the selection rules are mostly determined by the orientation of the q vector with respect to the electromagnetic fields. We observed a magnetic field history-dependent change in the strength and the frequency of the spin-wave modes, which we attributed to the change of the orientation and the length of the cycloidal q vector, respectively. Finally, we compared our experimental data with the results of linear spin-wave theory that reproduces the magnetic-field dependence of the spin-wave frequencies and most of the selection rules, from which we identified the spin-polarization coupling terms relevant for the optical magnetoelectric effect.
| Original language | English |
|---|---|
| Article number | 174429 |
| Journal | Physical Review B |
| Volume | 104 |
| Issue number | 17 |
| DOIs | |
| State | Published - Nov 1 2021 |
Funding
This research was supported by the Estonian Ministry of Education and Research Grants No. IUT23-3 and No. PRG736, by the European Regional Development Fund Project No. TK134, by the bilateral program of the Estonian and Hungarian Academies of Sciences under Contract No. NMK2018-47, by the Hungarian National Research, Development and Innovation Office—NKFIH Grants No. ANN 122879 and No. FK 135003. The research reported in this paper and carried out at the BME has been supported by the NRDI Fund (TKP2020 IES, Grant No. BME-IE-NAT) based on the charter of bolster issued by the NRDI Office under the auspices of the Ministry for Innovation and Technology. D.Sz. acknowledges the support of the Austrian Science Fund (FWF) [No. I 2816-N27 and No. TAI 334-N] and that of the Austrian Agency for International Cooperation in Education and Research [No. WTZ HU 08/2020]. R.S.F. acknowledges support by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.
| Funders | Funder number |
|---|---|
| Estonian and Hungarian Academies of Sciences | NMK2018-47 |
| NRDI | |
| TKP2020 IES | |
| U.S. Department of Energy | |
| Basic Energy Sciences | |
| Division of Materials Sciences and Engineering | |
| Austrian Science Fund | 2816-N27, TAI 334-N |
| Austrian Science Fund | |
| Haridus- ja Teadusministeerium | IUT23-3, PRG736 |
| Haridus- ja Teadusministeerium | |
| Österreichische Agentur für Internationale Mobilität und Kooperation in Bildung, Wissenschaft und Forschung | WTZ HU 08/2020 |
| Österreichische Agentur für Internationale Mobilität und Kooperation in Bildung, Wissenschaft und Forschung | |
| European Regional Development Fund | TK134 |
| European Regional Development Fund | |
| Nemzeti Kutatási Fejlesztési és Innovációs Hivatal | ANN 122879, FK 135003 |
| Nemzeti Kutatási Fejlesztési és Innovációs Hivatal | |
| Nemzeti Kutatási, Fejlesztési és Innovaciós Alap | |
| Innovációs és Technológiai Minisztérium |