Fe and Co NMR studies of magnetoelectric Co₂Y-type hexaferrite BSCFAO

Abstract

The Fe<sup>3+</sup> and Co<sup>2+</sup> NMR spectra for Ba<sub>0.3</sub>Sr<sub>1.7</sub>Co<sub>2</sub> (Fe<sub>0.96</sub>Al<sub>0.04</sub>)<sub>12</sub>O<sub>22</sub> (BSCFAO) and Ba<sub>0.3</sub>Sr<sub>1.7</sub>Co<sub>2</sub>Fe<sub>12</sub>O<sub>22</sub> (BSCFO) were obtained in a zero magnetic field at a low temperature. We observed change in the enhancement effect of the NMR signals depending on the setting field, which was varied when applied along the b-axis and then turned off before the measurement was taken. The experimental results indicate that the magnetic structure changes from an alternating longitudinal cone to a transverse cone when the setting field is 250 mT. They also show that the spins of Co<sup>2+</sup> ions together with those of Fe<sup>3+</sup> ions constitute a part of the overall magnetic structure and that the substitution of Al<sup>3+</sup> for Fe<sup>3+</sup> weakens the magnetic anisotropy within the easy plane. From a comparison of the enhancement factors of the Fe<sup>3+</sup> NMR obtained with the RF pulse applied along the a-axis and the c-axis, we realized that the magnetic easy plane anisotropy is approximately 16 times greater than the anisotropy within the easy plane. No changes of the NMR spectra were observed under an electric field of 1.2 MV/m.

Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5Sr1.5Co2Fe2O22

“…In particular, single phase multiferroics are of great interest for these multifunctional devices. Among the compounds with this characteristic, ferroxplana type hexaferrites with Z ([BaSr] 3 Me 2 Fe 24 O 41 ) and Y ([BaSr] 2 Me 2 Fe 2 O 22 ) phases are very promising materials, due to the giant magnetoelectric coupling between magnetism and ferroelectricity and low magnetic fields to switch the electric polarization [5,6]. In Z phase this behaviour is observed at room temperature, but single Z phase formation is still challenging.…”

“…Metal cations occupy four octahedral (18h VI , 6c VI , 3a VI and3b VI ) and two tetrahedral sites (6c IV and 6c IV *). Regarding the magnetic structure, the planes containing Ba and Sr ions have small net magnetic moments, whereas the rest of layers have large magnetic moments, so that we can consider them as S and L blocks [6], with a net moment perpendicular to the c axis. The substitution of Sr replacing Ba causes lattice deformation and hence the superexchange bond angles increase, especially the corresponding to the metal cations in the layers of Ba(Sr) ions.…”

Effective lightweight, flexible and ultrathin PVDF/rGO/Ba2Co2Fe12O22 composite films for electromagnetic interference shielding applications

“…The 36Fe 3+ ions in the unit cell are distributed among four octahedral sites: 18h VI , 3b VI , 3a VI , 6c VI and two tetrahedral sites: 6c IV * , 6c IV . Among the six different interstitial sites, three (18h VI , 3b VI , 3a VI ) have spin in the upward direction while the other three (6c VI , 6c IV * , 6c IV ) have spin in the downward direction [20]. In the literature, various reports on Y-type hexaferrites for microwave absorbers have focused on the enhancement of microwave absorption through substitution of various metal cations such as Zn 2+ , Co 2+ , Cu 2+ and Ni 2+ in the Me site in the chemical formula of Ba 2 Me 2 Fe 12 O 22 [21][22][23].…”