Pseudobrookite Fe2-2xCoxTi1-½xO5: Structural, magnetic phase transformation and reflection loss characteristic

Abstract

Single-phase pseudobrookite Fe2-2xCoxTi1-½xO5 (x = 0, 0.1, 0.2, and 0.4) with an orthorhombic structure has been successfully synthesized using a solid reaction and sintering at 1000 °C. Pseudobrookite Fe2-2xCoxTi1-½xO5 is an element that is abundant on earth and is attracting rapidly growing interest as a very promising candidate for the application of microwave absorbing materials. This paper studies the performance of exchange coupling in addition to the structural properties and microwave absorption characteristics of pseudobrookite Fe2-2xCoxTi1-½xO5. Qualitative and quantitative analysis of the X-ray diffraction (XRD) pattern show that all samples were single-phase pseudobrookite Fe2TiO5 with a space group of C m c m. The presence of Co causes the expansion of the lattice parameter with an indicator of an increase in the value of the unit cell volume as the composition of Co in the structure increases. Particle morphology and elemental composition were also observed using a scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). The presence of Co2+ dopant ions does not affect the shape and size of the particles, while the crystallite size increased with the increase in the content of Co2+ dopant ions in the structure and Co elements of 1.82, 2.81, and 5.69 at% have been detected, which are contained in the composition x = 0.1, 0.2, and 0.4, respectively. The presence of the Co2+ dopant ion it stimulates the rearrangement of the cationic distribution in both tetrahedral and octahedral sites which will have an impact on changes in the magnetic properties of this pseudobrookite. Magnetic properties were analyzed by measuring magnetization (M) against a magnetic field (H) at 300 K (RT). The spontaneous magnetization at room temperature in pseudobrookite Fe2-xCoxTi1-½xO5 is ∼2.55, 7.41 and 8.67 emu/g for compositions of x = 0.1, 0.2 and 0.4, respectively. The coercive field is ∼424, 356 and 284 Oe for compositions of x = 0.1, 0.2 and 0.4, respectively. The presence of Co in the structure causes a magnetic phase transformation from paramagnetic to ferromagnetic behavior at room temperature. This ferromagnetic behavior can be explained due to the strengthening of indirect exchange interactions of Ti/Co – O – Fe/Co in addition to the interactions of Fe/Co – O – Fe/Co and Ti/Co – O – Ti/Co, as well as changes in the degree of inversion of this pseudobrookite structure, due to the presence of magnetic ion dopants. Magnetic parameters both Ms, Mr, and Hc show an increase with increasing Co2+ ion content at room temperature. This magnetic parameter is very important at room temperature to determine the absorption characteristics of microwaves through the resonant frequency. Microwave absorption characteristics are measured in the 8–12 GHz frequency range. The best reflection loss (RL) peaks were obtained at composition x = 0.1 of -24 dB at 10.6 GHz frequency. The presence of Co2+ dopant ions can produce a very significant increase in RL almost 3 times at the same absorption frequency. This increase in reflection loss can be attributed to the effect of the magnetic phase transformation of this material which has been described accordance of the magnetic coupling exchange interaction, which in turn changes the magnitude of the relative permeability value of this material complex.