Temperature dependent broadband dielectric, magnetic and electrical studies on Li1-xMg2xFe5-xO8 for microwave devices

Polycrystalline samples of Mg substituted lithium ferrites (Li1-xMg2xFe5-xO8 (LMFO) (x = 0, 0.003, 0.005, 0.007 and 0.01) have been prepared by conventional solid-state reaction. X-ray diffraction patterns revealed the formation of a single-phase cubic structure with P4132 space group. The dielectric constant of lithium ferrite increased with Mg substitution attaining a maximum value for x = 0.005 (εr = 3034, tan δ = 0.001at 1 MHz) at room temperature. Temperature-dependent dielectric response in the high frequency range (1 MHz–1 GHz) showed the relaxor behaviour of the dipoles, evident from the shift in the loss tangent with frequency. The activation energy of LMFO is found to be in the range of 1.39 - 0.35 eV. An enhanced permeability is found to be ∼29 for x = 0.007 at 1 MHz, RT. The variation in permeability is attributed to the variation in thickness of the domain walls and magneto-crystalline anisotropy. The temperature-dependent magnetization curves reveal the ferrimagnetic transition of LFO at 600 °C, which reduced with Mg substitution. Magnetic hysteresis loops showed the highest saturation magnetization (Ms = 54.6 emu/g) for x = 0.007 among all the samples. The magnetic properties are explained by considering Neel’s two sub-lattice model. Thus, LMFO samples, (especially with x = 0.005) are very promising for circulator and phase shifter applications.

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