Complex permittivity, complex permeability and reflection loss of Co-Zr substituted La-Sr hexaferrites in 18–40 GHz frequency range

Highlights

• Synthesized ferrites show microwave absorption of more than 99%.

• Minimum RL in the range of −18.15 dB to −28.69 dB.

• Bandwidth (−10 dB) of 5.87 GHz obtained for x = 1.00 in Ka-band.

• These ferrites can be used as efficient microwave absorbing material.

Abstract

In this research, electromagnetic and microwave absorption properties of the hexagonal ferrites with chemical composition, Sr_0.85La_0.15(CoZr)_xFe_12-2xO₁₉ (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were studied in the K-band (18–26.5 GHz) and Ka-band (26.5–40 GHz) frequency range. Minimum reflection loss (RL) was successfully optimized in the studied frequency range by tuning sample thickness using quarter-wavelength criterion. Absorption results of synthesized hexagonal ferrites show minimum RL in the range of −18.15 dB to −28.69 dB and absorption bandwidth (−10 dB) in the range of 1.04 GHz to 5.87 GHz. The microwave absorption significantly improved with absorption bandwidth (−10 dB) of 5.87 GHz for the composition x = 1.00 at a sample thickness of 2.2 mm. These newly synthesized ferrites have high potential as microwave absorbing material for military applications such as camouflaging of the target and also as EMI (Electromagnetic Interference) suppressor.

Introduction

Now-a-days the level of electromagnetic (EM) pollution has increased due to a rapid growth in the modern electronic and information technology. The unwanted electromagnetic radiation causes electromagnetic interference (EMI) which results in poor performance of the electronic and microwave devices. Furthermore, this increased electromagnetic pollution has shown sign of harmful effects on human beings and environment [1]. The microwave absorber is the best solution to reduce such unwanted microwave radiations. M-type hexagonal ferrites can effectively work as EM wave absorbers due to their better dielectric and magnetic properties [2], [3]. In this respect, the design of efficient microwave absorbers in X-, Ku-band is of great interest to the researchers in the last two decade [3], [4], [5], [6], [7], [8]. Two prerequisite conditions for EM wave suppression by the material must be satisfied: First, the EM wave must enter the material without front-end reflection and second, the EM wave which entered the material must be attenuated to acceptable level. Strong absorption, wide bandwidth and small sample thickness are the significant features of efficient microwave absorbers. However, relatively few papers have investigated hexagonal ferrites as efficient microwave absorbers in K and Ka-band frequency range qualitatively [9], [10], [11]. Many researchers have modified the structural, dielectric, magnetic and electromagnetic properties of M-type hexagonal ferrites by substitution of Fe³⁺ ions with various divalent-tetravalent ion combinations [2], [3], [4], [5], [6], [7], [8], [9], [10], [11] and/or substitution of Sr²⁺ ion with La³⁺ ion [12], [13]. Narang et al. [9] investigated the electromagnetic and microwave absorption properties of M-type Co-Ti doped barium hexagonal ferrites in 18–40 GHz frequency range and observed that the sample with x = 0.2 achieved minimum reflection loss of −44.56 dB. Dong et al. [10] studies microwave absorption properties of Co-Ti doped barium hexaferrites and results showed low reflectivity of these ferrites in the Ka-band. Pubby et al. [11] prepared hexaferrites with general formula Sr(CoZr)_xFe_12-2xO₁₉ using so-gel auto-combustion method and observed that the sample with x = 0.2 has maximum absorption capacity with reflection loss peak of −37.2 dB at 24.3 GHz frequency. Chemical methods for synthesis of ferrites are based on low sintering temperatures, which are known to enhance the magnetic properties of hexagonal ferrites due to transition of grain size from micrometer to nanometer range [14].

The aim of this research work is to investigate microwave absorption performance of the synthesized hexagonal ferrite with composition formula, Sr_0.85La_0.15(CoZr)_xFe_12-2xO₁₉ (x = 0.00, 0.25, 0.50, 0.75 and 1.00) in 18–40 GHz frequencies for their usage in electronic material industry as microwave absorbers with wide absorption bandwidth. To the best of author’s knowledge K- and Ka-band study on this composition using citrate auto-combustion method has not been studied so far.