Effects of Al substitution and thermal annealing on magnetoelectric Ba_0.5Sr_1.5Zn₂Fe₁₂O₂₂investigated by the enhancement factor of⁵⁷Fe nuclear magnetic resonance

Abstract

The magnetoelectric properties of hexaferrite Ba0.5Sr1.5Zn2Fe12O22 are significantly improved by Al substitution and thermal annealing. Measuring the enhancement factor of 57Fe NMR, we found direct microscopic evidence that the magnetic moments of the L and S blocks are rotated by a magnetic field in such a way as to increase the net magnetic moment of a magnetic unit, even after the field is removed. Al substitution makes magnetoelectric property arise easily by suppressing the easy-plane anisotropy. The effect of thermal annealing is to stabilize the multiferroic state by reducing the number of pinning sites and the electron spin fluctuation. The transverse conic structure gradually changes to the alternating longitudinal conic structure where spins fluctuate more severely.

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

“…The EF increases as the TC structure induced by the setting field develops a net magnetic moment in the baxis direction. The same phenomenon was also observed in Zn 2 Ytype hexa ferrite [19]. The setting field required to change the magnetic structure from ALC to TC in BSCFAO is approximately 250 mT, which is one order of magnitude larger than that in Zn 2 Ytype hexaferrite.…”

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba0.3Sr1.7CoxMg2−xFe12O22*

“…Previous studies suggest that there are several factors that influence the ME properties of Y-type hexaferrites, such as the annealing process, the sintering temperature, and the ion substitution. [23][24][25] Extensive studies have been performed to investigate the effects of different ion substitutions on the ME properties of Y-type hexaferrites. [26][27][28][29] It was re-ported that the critical magnetic field for inducing electrical polarization becomes rare low when Mg replaces Zn to form the Y-type hexaferrite Ba 2 Mg 2 Fe 12 O 22 .…”

Room-temperature magnetoelectric effects in multiferroic Y-type hexaferrites

“…In addition, the ME properties of Y-type hexaferrites depend on numerous factors like ion substitution, the sintering temper ature, and the annealing process [25][26][27]. Extensive researches have focused on the ion substitution to improve the ME properties of hexaferrites [28,29].…”

“…Therefore, further investigations are needed in order to understand and improve the ME properties at RT for BaSrCo 2 Fe 11 AlO 22 . Ion substitution has become an effective way in improving the ME properties of Y-type hexaferrites [28]. Sr doping can tune the magnetic transition temperatures [30] and strengthen the exchange interactions [31].…”