Study on Electrical and Magnetic Properties of Modified Strontium Hexaferrite (SrFe12O19)

Abstract

Electric and magnetic properties of bulk and nano strontium hexaferrite and modified with Co2+, Ti4+ and Co2+-Ti4+ in micro level have been investigated. Bulk strontium hexaferrite (SrFe12O19) system was prepared by conventional solid state route and nano SrFe12O19 system was prepared by auto combustion method of the chemical route. The contribution of microstructures (intrinsic grain and extrinsic grain boundary, sample surface-electrode contact) to the conduction mechanism was investigated by complex impedance spectroscopic analysis. Only the extrinsic (electrode polarization)conductions were observed in the bulk strontium hexaferrite system at room temperture whereas intrinsic grain and grain boundary conduction is found present in its nano SrFe12O19 system. It is observed that the saturation magnetization of bulk strontium hexaferrite was found to be higher than nano system. However, coercivity is higher in nano- strontium hexaferrite which can be related to the surface spin effects.

Cobalt substituted strontium hexaferrite (SrFe12-xCoxO19,x=0.45) samples were prepared by solid state method. The single phase XRD pattern confirmed the successful substitution of the larger cation. Surface morphology from SEM image indicated the particle growth (6μm – 7μm) as an effect of Cobalt substitution. The increased grain size has effectively modified the electrical properties of the system in three major ways: (a) increase in resistivity, (b) evolution of grain relaxation and (c) reduction in dielectric loss and surface conduction. Additionally, magnetic behaviour is also affected due to control particle growth. Magnetic hysteresis study at room temperature confirmed the reduction in saturation magnetization (MS = 83 to 85 emu/g.) and coercivity (HC = 457 to 3991Oe).

Titanium substituted Strontium hexaferrite (SrFe11.7Ti0.225O19) which is synthesized by solid state method. The single phase XRD pattern confirmed the successful substitution and Surface morphology from SEM image indicated the grain growth (800nm –1.59μm) as a result of Titanium substitution. Ac electrical properties were measured within frequency window of 100 Hz to 1 MHz in the range of temperature of 303K to 523K. At room temperature (303K) single relaxation peak appears in imaginary impedance plot throughout the studied temperature which attributes to grain boundary effect. The increased particle size has effectively modified the electrical properties of the system in three major ways: (a) decrease in resistivity, (b) evolution of grain boundary relaxation and (c) increase in dielectric loss and reduction in surface conduction. Magnetic hysteresis study at room temperature confirmed the rise in saturation magnetization (MS = 88 to 85 emu/g.) and reduction in coercivity (HC = 2183 to 3991Oe).

Cobalt-Titanium Co-substituted Strontium hexaferrite (SrFe11.7Co0.225Ti0.1125O19) which is synthesized by solid state method. The single phase XRD pattern and the surface morphology from SEM image indicated the longitudinally grain growth (2.55μm –3μm) as a result of Cobalt-Titanium Co-substitution. The increased particle size has effectively modified the electrical properties of the system in three major ways: (a) increase in resistivity, (b) evolution of grain relaxation and (c) reduction in dielectric loss and surface conduction. Additionally, magnetic behaviour is also affected due to control particle growth. Magnetic hysteresis study at room temperature confirmed the rise in saturation magnetization (MS = 117 to 85 emu/g.) and reduction in coercivity (HC = 257 to 3991Oe).

The thesis provides some qualitative information regarding the titled compound which will benefit the other researchers to go for further magnetic and non-magnetic modifications. The properties of the modified systems are also suitable to be used in microwave applications.