VP10-02: Shape Effects on Magnetic Behaviors of Sr-substituted BaM Ferrite Substrates Applied for Self-biased Circulators

For ferrite substrate of self-biased circulators[1], high coercivity is beneficial to inhibit irreversible demagnetization[2], which can enhance the remanence (4πMr) and its stability. Now, some researches have focused on the field. V. Laur et al. [3] have proposed the (La-Co)x-SrM hexaferrite pucks applied in the self-biased Y-junction rectangular waveguide circulators. Xu Zuo et al. [4] have demonstrated a self-biased microstripline circulator/isolator using SrM ferrite, in which the hexaferrite disk was embedded in the alumina substrate. Considering that magnetic behaviors have closed relationship with the shape of the ferrite substrate. We present the shape effect on the magnetization behavior and mechanism of ferrite substrates. BaSrM ferrite were developed with magnetic pressing, with the composition of Ba0.8-xSrxLa0.2Fe10.4Cu0.2O16.9 (where 0.2 ≤ x ≤ 0.8). Two types of samples named sample 1 (S1) and sample 2 (S2) were prepared as shown in Fig.1. 4πMs is determined via S1, and magnetic properties of the ferrite substrate are determined via S2 which are presented in Table 1. Phase formation and texture structure of the BaSrM were confirmed by XRD patterns and EBSD figures. HAADF pictures and mappings of the sample with x=0.4 exhibit the obvious textural orientation and the element distribution. Magnetic hysteresis loops of the substrates possess good anisotropy behaviors. Coercivity (Hc) reaches the maximum when x=0.4. Effects of substrate shape on the M-H curves were investigated, and the results show that saturation magnetization cannot be achieved if the aspect ratio (h/l) is less than 34.9% resulting from the strong demagnetizing field (Hd), though the magnetic field along z direction of the substrate is applied to 20 kOe. So the maximum magnetization is expressed as Mm. With the increase in aspect ratio, Mr/Mm is enhanced significantly. In addition, magnetic flux density versus the aspect ratio of the substrate was simulated by ANSYS Maxwell software, and the results reveal that enhancing the aspect ratio is a key method to enhance remanence of the textured hexaferrite in z direction.References: [1]W. M. Gitzel, S. B. Rad, M. Heidenreich, et al. Integration concept for a self-biased Ka-band circulator[C]. 2020 23rd International Microwave and Radar Conference (MIKON). IEEE, 2020: 350-352. [2] Robert C. Pullar, Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics, Progress in Materials Science, 57, 2012:1191-1334. [3]V. Laur, G. Vérissimo, P. Quéffélec, et al. Self-biased Y-junction circulators using lanthanum-and cobalt-substituted strontium hexaferrites. IEEE Transactions on Microwave Theory and Techniques, 63(2), 2015:4376-4381. [4]X. Zuo, H. How, S. Somu, et al. Self-biased circulator/isolator at millimeter wavelengths using magnetically oriented polycrystallline strontium M-type hexaferrtie. IEEE Transactions on Magnetics, 39(5), 2003:3160-3162.