Impact of Gd doping on the dielectric and magnetic properties of (Sr–Ba) Fe12O19 nanoparticles

Abstract

Composition Ba0.5Sr0.5Fe12-xGdxO19, where x = 0 to 0.4 in steps of 0.1 was synthesized by Without Water and Without Surfactant (WOWS) Sol-Gel method. The synthesized powder was calcined and sintered at 910 °C/20 min and 920 °C/20 min, respectively. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques to study phase purity, surface morphology and particles shape of the samples, respectively. There is no change in the lattice constant value of ‘a’ but value of ‘c’ showed small change in undoped and Gd-doped mixed 0.5Sr-0.5Ba hexaferrite samples. SEM micrographs revealed that particles shape is spherical and grains size reduced up to x = 0.4 Gd doping. Grain size was from 180 to 130 nm. Dielectric properties were measured from 20 Hz–3 MHz at room temperature. The dielectric constant,ε, values were high in frequency range from 20 to 600 Hz and dielectric loss tangent, tanδ showed low values from 20 Hz to 3 kHz. However, in high frequency regions both values were not sensitive to the frequency changes. It is also observed that ε, values of all Gd doped samples are high (except 0.2 Gd doped) and tan δ values of all Gd doped samples are low as compared to the undoped sample. The AC conductivity, σac values remained almost constant in the low frequency region up to 6 kHz and showed exponential increase in the frequency region >6 kHz. AC Electrical conductivity of all Gd doped samples is high as compared to undoped sample. These changes are explained by Maxwell-Wagner model. Cole-Cole plots showed that changes in the electrical properties of the undoped and Gd doped mixed 0.5Sr-0.5Ba hexaferrite sample is due to the change in grains size and grain boundaries resistance. The vibrating sample magnetometer, VSM was used to study magnetic properties. Values of coercivity, Hc decreased for x = 0.1 Gd doped sample as compared to undoped sample. Further increase in Gd doping concentrations leads to increase in Hc values and highest value of 6202 Oe is observed which is close to the theoretically predicted value. However, saturation magnetization, Ms and remanence, Mr values increased for doped samples up to x = 0.2 Gd and then further doping decreased these values. The 0.1 Gd doped 0.5Ba-0.5Sr ferrite material may be used in the recording media devices.