Fig 1.
(a) XRD pattern of SrFe12O19 with O2 annealing process. (b) the standard diffraction pattern of the SrFe12O19(PDF#33–1340) being marked by discrete red lines.
Fig 2.
Modules of the complex impedance for (a) the conventional SrFe12O19 ceramics being sintered at 1150°C in air only, (b) the sintered ceramic was subsequently annealed in pure oxygen atmosphere at 800°Cfor 3 hours, (c) the annealed ceramic was flipping over and once again heat treated in O2at 800°C for another 3 hours.
Fig 3.
Complex impedance spectrum of the SrFe12O19 ceramic within the frequency range of 0.01 Hz to 1 MHz, (a) for the ceramic being sintered at 1150°C in air only; (b) for the sintered ceramic with subsequent annealing in O2.
Fig 4.
The equivalent circuit for the complex impedance of SrFe12O19 ceramics, the scheme is composed of two series linked sub-circuits with a capacitor and a resistor parallelly connected.
Fig 5.
XPS spectrum for Fe 2p energy levels of the sintered SrFe12O19 ceramics (a) with O2 treatment and (b) without O2 treatment.
The insets display the upper Fe2p1/2 and Fe 2p2/3 lines for the two specimens, respectively.
Fig 6.
Valence band spectra of SrFe12O19 ceramics (a) with O2 heat treatment and (b) without O2 heat treatment.
The dotted lines marked the top of the valence band.
Table 1.
Valence band states assignment.
Fig 7.
Plot of dielectric constant as a function of temperature for SrFe12O19 ceramics with O2 treatment at frequencies of (a) 1kHz, (b) 10kHz and (c) 100 kHz.
Fig 8.
Modified Curie-Weiss law calculation.
(a) Logarithm of (1/ε-1/εd) as a function of logarithm of (T-Td) at 10 kHz. and (b) logarithm of (1/ε-1/εm) as a function of logarithm of (T-Tm) at 100 kHz for the SrFe12O19 ceramic being sintered at 1150°C for 1 hour and subsequently annealed in O2 for 9 hours with 3 steps wise.
Fig 9.
(a) The saturated ferroelectric polarization hysteresis (P-E) loop, and (b) a plot of current as a function of voltage (I-V curve) of SrFe12O19 ceramic.
The ceramic has been sintered at 1150°C for 1 hour and subsequently annealed at 800°C in pure oxygen for a total duration of 9 hours in 3 steps wise. The measurement was made at a frequency of 33Hz and room temperature (300K).
Fig 10.
Magnetic hysteresis loop of SrFe12O19 (a) being sintered at 1150°C for 1 h and subsequently annealed in O2 for 9 hs with 3 steps wise, (b) without heat-treatment in O2.
Fig 11.
Giant magnetocapacitance effect: (a) B-dependent magnetic permeability (μr) and delimited magnetic phase profile; (b) variable dielectric constant as a function of B field for the O2 treated SrFe12O19 ceramics at a frequency of 100Hz and room temperature (300K).