Magnetic and microwave absorbing properties of low-temperature sintered BaZr Fe_(12-O₁₉

In the present work, to enhance the reflection loss and change the magnetic resonance frequency of barium ferrite sintered at low temperature, different amounts of Zr ion were introduced to BaFe₁₂O₁₉ to substitute the Fe ion. A series of M-type barium hexaferrite samples having the nominal composition BaZr Fe_(12-O₁₉ (x = 0.0, 0.3, 0.6, 0.9 and 1.2) was successfully synthesized by heat treatment at a relatively low temperature (900 °C) for 2 h. In order to study the phases, morphologies and magnetic properties of the substituted barium ferrites, X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) were used. The XRD patterns indicated that all samples were single phase M-type ferrites. The SEM images showed that all samples were hexagonal-shaped particles and the average size was about 500 nm. Simultaneously, a potassium chloride additive can effectively reduce the sintering temperature of barium ferrites and their formation and morphology are apparently not affected. The VSM results demonstrated that the coercivity steeply decreased from 4772.43 Oe to 797.34 Oe when the Zr ion substitution amount increased from 0.0 to 1.2 but the saturation magnetization remained almost constant (M _s = 49.71-63.06 emu g^-1). Furthermore, the complex electromagnetic parameters were collected by a vector network analyzer (VNA) and the microwave absorbing properties were calculated according to transmission theory. It was found that the reflection loss is enhanced with increasing x. The minimum reflection loss value of -30.2 dB at 16.75 GHz was observed and the bandwidth is about 2.46 GHz for the x = 1.2 sample. BaZr Fe_(12-O₁₉ might be a promising candidate for applications of LTCC (low-temperature co-fired ceramic) substrates for millimeter wave circulators and filters.