Influences of different Bi2O3 additive amounts on static magnetic characteristics, micromorphology and ferromagnetic resonance linewidth of M-type Sr hexaferrites

Abstract

Considering the improvement of electronics regarding high frequency and miniaturization, SrM hexaferrites need to exhibit high anisotropy field Ha, high remanence ratio Mr/Ms, and low ferromagnetic resonance linewidth ΔH to create microwave devices and equipment with planarisation, miniaturisation, and high frequencies. The key to achieving self-biased microwave devices with high-frequency is to simultaneously achieve high Ha, high Mr/Ms, and low ΔH. However, it is hard to meet these requirements. In this study, Sr0.4La0.3Ca0.3Fe11.85Al1.0Co0.15O19 was used to study the effect of different doping amounts of Bi2O3 on its magnetic characteristics, micromorphology and FMR linewidth. With the increase of Bi2O3 doping, the grain size of the sample gradually increased, and the uniformity of the grain size gradually decreased. When the Bi2O3 doping amount x increased from 0 to 1.2 wt%, the 4πMs and 4πMr values increased and the coercivity displayed the opposite tendency. The samples showed great uniaxial anisotropy. The magnetocrystalline anisotropy field Ha shows a trend of initially decreased and then increased. When x = 1.0 wt%, Ha reaches the maximum value of 28.9 kOe. At this time, the ferromagnetic resonance linewidth ΔH of the sample is 1578 Oe. The theory of IGA was adopted to divide the FMR linewidth into two parts ΔHa and ΔHp. Accroding to the results, ΔHa takes the bigger proportion of linewidth. However, the change in ΔHp is not negligible. When x = 1.0 wt%, the sample showed its best performance (4πMs = 3412 Gs, 4πMr = 2905 Gs, Hc = 2649 Oe, Mr/Ms = 85.1%, large Ha = 28.864 kOe, and ΔH = 1578 Oe). The SrM ferrite materials provided in this study can potentially be used in the microwave engineering, high-frequency, and self-biased devices.