Co–Al-substituted strontium hexaferrite for rare earth free permanent magnet and microwave absorber application

Abstract

Permanent magnets (PMs) have tremendous demand because of their applicability in various electronic devices. Rare earth (RE) elements are the major component in fabricating these PMs. Tremendous research interest has been generated over the last decade to design the RE-free PMs because of the ever-increasing cost of REs and shortage of their supply. Hexagonal ferrites show incredible potential as RE-free magnets owing to their high coercivity and moderate saturation magnetization. In this work, we focused on improving the magnetic properties of Sr0.8Ca0.2AlxCoxFe12−2xO19 hexagonal ferrites with respect to Co2+–Al3+ co-substitution synthesized by the sonochemical method. Improved saturation magnetization of 64.4 emu g−1, coercivity of 13.2 kOe, and a remnant ratio of 0.71 was achieved upon Co2+–Al3+ substitution. The prepared materials were also tested for microwave absorption characteristics, where a maximum reflection loss of −35.4 dB at 12.36 GHz was obtained. Results were discussed in light of the synthesis method, Co2+–Al3+ substitution, and electrical properties. Such improvement in the electromagnetic properties make these ferrites suitable for use as RE-free PMs and microwave absorbers.

Aluminum Doping and Nanostructuring Enabled Designing of Magnetically Recoverable Hexaferrite Catalysts

“…A similar feature of increase in H c has been reported for the Al-doped strontium hexaferrite in the literature. 7 , 15 The decrease in M s and the increase in H c for the Al-substituted SFO can be understood based on the two primary considerations. The crystallite size of Al-doped SFO smaller than that of the parent counterpart (SFO) is the first.…”

“… 1 , 3 , 7 , 11 , 12 Due to its superior magnetic parameters, high permeability, and low conductivity loss, SFO has been widely used in numerous technological applications, which include permanent magnet designs, microwave absorbers, magnetic recording media and sensors, high-frequency electromagnetic (EM) devices, EM shielding devices, and so forth. 1 , 3 − 7 , 10 …”

“… 2 Similarly, nanostructuring of SFO is shown to enhance the property and performance effectively. 3 − 7 SFO nanomaterials with highly aligned nanocrystallites combined with crystal growth during spark plasma sintering (SPS) exhibit enormous enhancement of the magnetic properties compared to the as-synthesized powders, leading to high-performance bulk magnets with high-energy products (26 kJ m –3 ). 4 , 5 Based on the extensive work, Christensen and team proposed a complete bottomup nanostructuring protocol for preparation of magnetically aligned, high-performance hexaferrite permanent magnets with a record-high (BH) max for dry-processed ferrites.…”

Excellent Microwave Absorbing Properties of Nd3+‐Doped Ni–Zn Ferrite/PANI Nanocomposite for Ku Band

“…The RL was calculated from complex permittivity and permeability data. The RL is a function of the coefficient of reflection of wave and can be represented by the following equation [ 11,15 ] where Z 0 is the impedance of free space, is the impedance of the absorber, and are the complex relative permittivity and permeability of free space, respectively, f is the EM wave frequency, t is the thickness of the absorber, c is the velocity of microwaves in free space, and μ r and ε r are the measured relative complex permeability and complex permittivity, respectively.…”

“…[5][6][7][8][9][10] There is an increasing demand of electronic devices such as wireless communication devices, local area network (LAN) systems, computers, bluetooth technologies, high-speed data-transferring devices, and medical diagnostic tools which are operating in the microwave frequency range. [11,12] It resulted in electromagnetic interference (EMI), which is the disturbance that affects an electrical circuit of a device due to an electromagnetic radiation from another electrical circuit and signal degradation in microwavebased electric devices.…”