Crystal and magnetic structures and their temperature dependence of Co2Z-type hexaferrite (Ba,Sr)3Co2Fe24O41 by high-temperature neutron diffraction

Abstract

We have prepared nonoriented and magnetically oriented specimens of Co2Z-type Ba ferrite Ba3Co2Fe24O41 (Ba3Z) and those with Sr2+ substitution for Ba2+, i.e., Ba1.5Sr1.5Co2Fe24O41 (Ba1.5Sr1.5Z) and Sr3Co2Fe24O41 (Sr3Z) with the conventional solid-state reaction method. Permeability measurements of nonoriented specimens have shown that this substitution improves the frequency characteristic of permeability, though the permeability in Sr3Z significantly decreases. X-ray diffraction (XRD) and magnetization measurements of magnetically oriented specimens have shown that the magnetic moments of iron and cobalt ions in Ba3Z and Ba1.5Sr1.5Z lie in the c plane, but that those in Sr3Z deviate from the c plane. We have studied the substitution effect of Sr2+ for Ba2+ on the crystal structures and the effective sizes and directions of magnetic moments and their temperature dependences with high-temperature neutron diffraction technique. This substitution induces the change in the distribution of cobalt ions and moment directions of magnetic ions. Magnetic moments in Ba3Z and Ba1.5Sr1.5Z turn to the c axis when temperature rises from 523to573K. However, the moments in Sr3Z turn to the c axis at the lower temperature of 50K. These results were consistent with the present measurements on permeability, XRD, and magnetization. The change in moment direction caused by temperature rise must be attributed to the disappearance of effective moments of cobalt ions in these temperature regions.

Electromagnon in theZ-type hexaferrite(BaxSr1−x)3Co2Kadlec1, Kadlec2, Vít3 et al. 2016Phys. Rev. B28080View full textAdd to dashboardCite

“…This is in agreement with the known literature; up to now, in the structural studies of Z-hexaferrite (Ba x Sr 1−x ) 3 Co 2 Fe 24 O 41 , no polar space group was resolved 23,24 and the electric polarization P ⊥ z was observed only in an external magnetic field. 3,8 Nevertheless, for final proving or disproving of the polar crystal structure, we propose further complementary experiments, such as second-harmonic generation or high-resolution electron diffraction.…”

Multiferroic and Magnetoelectric Hexagonal Ferrites

“…This also resulted in the magnetic moment of the cobalt ions being quenched between 200-250°C in Sr 3 Co 2 Z, 50-100°C lower than the other Co 2 Z ferrites. Takada et al also observed the two-step magnetisation loop first reported by Pullar and Bhattacharya, and noted that in oriented polycrystalline samples this effect [68] was much more pronounced when the applied field was measured along the easy direction (c-axis) [94]. Such features were not seen in the Sr 1.5 Ba 1.5 Co 2 Z magnetisation loops.…”

“…However, in oriented polycrystalline Sr 3 Co 2 Z the easy axis of MCA was in a cone at an angle of 52.3°to the c-axis at RT, [94] and remained so up to 200°C, before rapidly decreasing further to *25°at only 250°C, and moving fully to the c-axis at the same temperature as the other Co 2 Z ferrites [68]-so it is uniaxial at room temperature, despite being a very soft ferrite. From neutron diffraction data, the ions filling the ten different possible Wyckoff positions for iron and cobalt ions were obtained by Takada et al This demonstrated that, while in Sr 1.5 Ba 1.5 Co 2 Z cobalt occupies six sites (Me1(2a), Me2(4f), Me4(12 k), Me5(4e), Me8(12 k) and Me10(2d)), in Sr 3 Co 2 Z cobalt only occupies the first four of these [68]. This means that Co 2+ is not present in the Me8(12 k) or Me10(2d) positions-in other words, it is not present at all in the R block of Sr 3 Co 2 Z, unlike in other Co 2 Z ferrites (Fig.…”

“…It was observed that for Ba 1.5 Sr 1.5 Co 2 Z the anisotropy lay in the basal plane at RT, and with increasing temperature up to 250°C this angle slowly decreased from 90°to *70°, at which temperature the angle began to rapidly decrease to *20°at [66] 300°C, and the ferrite became fully uniaxial at 400°C [68]. However, in oriented polycrystalline Sr 3 Co 2 Z the easy axis of MCA was in a cone at an angle of 52.3°to the c-axis at RT, [94] and remained so up to 200°C, before rapidly decreasing further to *25°at only 250°C, and moving fully to the c-axis at the same temperature as the other Co 2 Z ferrites [68]-so it is uniaxial at room temperature, despite being a very soft ferrite.…”

“…Sr 3 Zn 2 Z was reported in 1970, [65] (Fig. 7.12) [68]. A citrate route has also been used to make Sr 3 Co 2 Z, from precursor powders pyrolised at 400-450°C, and then calcined at 1,200°C/5 h in air.…”