Abstract:
Five series of strontium hexaferrite nanomaterials with nominal compositions,
SrZrxNixFe12-2xO19, SrZrxCuxFe12-2xO19, SrZrxMnxFe12-2xO19, SrZrxZnxFe12-2xO19 and
SrZrxAlxGaxFe12-2xO19 (where x = 0.0-0.8) have been synthesized by the chemical co-
precipitation method. The structural analysis is carried out by thermogravimetry
(TG/DTG), powder X-ray diffraction (XRD) and energy dispersive X-ray
fluorescence (ED-XRF) techniques. The DC electrical resistivity (ρ), dielectric
constant (έ) and dielectric loss (tanδ) are measured by a two-point probe method and
inductance capacitance resistance (LCR) meter, respectively. The magnetic
susceptibility (χ) is measured by a magnetic susceptometer and the hysteresis loops,
the saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) has been
determined by the induction method. Thermal analysis reveals that the
magnetoplumbite phase begins to form at a temperature of 873 K and is completed at
1193 K which is also complimented by the XRD studies. The average crystallites
sizes of the samples of the five series are in the range of 26-62 nm. All the samples
consist of pure single phase as confirmed by the magnetic susceptibility and XRD
analysis. The nominal theoretical compositions of the samples are experimentally
confirmed by the ED-XRF analysis. Except Zr-Mn substituted series all the samples
show metal to semiconductor transition (TM-S). The drift mobility (μd) and activation
energy (Ea) are calculated from the electrical resistivity data. The observed variation
of electrical resistivity is explained on the basis of the electrons hopping between
ferric and ferrous ions. The room temperature electrical resistivity and activation
energy are increased by doping with Zr-Ni, Zr-Cu, Zr-Mn and Al-Ga series up to
specific concentration but decreases continuously by substitution of Zr-Zn. The
dielectric constant (έ) and dielectric loss (tanδ) are calculated in the frequency range
of 100 Hz -1MHz and both the parameters decrease with increase in frequency. This
behavior is explained on the basis of the Maxwell- Wagner and Koop’s models. The
dielectric constant, dielectric loss and drift mobility increase with the increase in the
dopant (Zr-Ni, Zr-Cu, Zr-Mn and Al-Ga) contents but increase by the substitution of
Zr-Zn. The Curie temperature (Tc) is determined from the temperature dependence of
magnetic susceptibility (χ) at temperature from 300 to 800 K. the value of Tc
decreases for all the five series investigated here. The saturation magnetization (Ms)
increases for Zr-M series (where M = Ni, Cu, Mn and Zn) but decreases for the Al-Ga
series. The coercivity (Hc) decreases for all the present series. The variation of
saturation magnetization,remanence (Mr) and coercivity with substituent concentration is explained on the basis of occupation of the substituted cations at
different hexagonal sites. The increase in saturation magnetization, electrical
resistivity and decrease in coercivity, dielectric constant, dielectric loss and drift
mobility suggest that the Sr-hexaferrites doped with Zr-Ni, Zr-Cu and Zr-Mn are
suitable for applications in high density recording media as well as in microwave
devices but the Zr-Zn and Al-Ga substituted samples are more suitable for high
density recording media and microwave devices, respectively.