Magnetic and broadband dielectric studies of calcium-substituted LiFe5O8

Abstract

The non-magnetic element Ca is substituted in LiFe5O8 (x = 0, 0.003, 0.005, 0.007 and 0.01) and the effect of Ca on magnetic, dielectric and electrical properties over a broadband frequency and temperature range (both at cryogenic and high temperatures) are investigated in order to check their suitability in microwave devices. The X-ray diffraction (XRD) study revealed the increment in the lattice constant and volume, which is also confirmed from the redshift in F2 Raman mode. The M-T curves of all the samples exhibited a ferromagnetic transition around 873 K. The effective magnetization and saturation magnetization is reduced with Ca substitution due to the incorporation of non-magnetic ions in place of magnetic ions, whereas the coercivity and remanent magnetization enhanced. These changes are explained based on Neel's two-sublattice model. The x = 0.007 specimen exhibited the highest permeability (µr = 28 @ 1 MHz, room temperature (RT) and µr = 52 @ 1 MHz, 523 K) among all the Ca substituted samples. Both the permittivity and permeability showed dispersion behavior with temperature. With Ca substitution, the permittivity improved, whereas the dielectric loss tangent (tanδ; order of 10−3) reduced. The activation energy is found to be 0.14 eV and 0.06 eV for x = 0 and 0.007, respectively. The reduction in activation energy can be ascribed to the creation of oxygen vacancies. A combination of permeability, low tanδ, enhanced permittivity, and high saturation magnetization obtained for the x = 0.007 sample is suitable for the applications in circulators and phase shifters.