We report the effect of the variation
of diameter on the optical,
magnetic, and magnetodielectric properties of the Pr–Cr-codoped
BiFeO3 (BFO) nanowires (NWs). Pr–Cr-codoped BFO
NWs with different diameters (18, 35, 55, 100, 150, and 250 nm) have
been fabricated by employing a simple wet chemical template-assisted
route. The effect of quantum confinement has been found to have a
significant influence on the room-temperature photoluminescence and
Raman spectra of the NWs. An interesting blue shift in the band gap
emission is observed in the photoluminescence spectra of the NWs as
a result of quantum confinement. The position and the intensity of
the Raman peaks are found to change significantly depending on the
variation in the NW diameter. The room-temperature ferromagnetism
of the codoped BFO NWs increases consistently with the decrease in
the diameter of the NWs because of the suppression of the spiral spin
structure and the increase in the number of uncompensated for spins
at the NW surface (as the surface to volume ratio increases with the
decrease in the NW diameter). Strong magnetoelectric coupling is evidenced
in the codoped BFO NWs with the decrease in the NW diameter. The tuning
of the optical, magnetic, and magnetodielectric properties of the
doped BFO NWs appears to be very promising for achieving multifunctionality
in a single material.
Enhanced magnetoelectric coupling is observed in bismuth ferrite samples, co-doped with non-magnetic Ba and magnetic Gd ions replacing Bi and Fe, respectively. Distortion in Fe–O octahedra has a significant effect on the magnetic properties of the samples. Ferromagnetic signature is found to increase significantly in the co-doped samples with respect to the only-Gd-doped sample both at 80 and 300 K. The co-doped samples show enhanced electric polarization as well as the highest resistivity at room temperature, which might be due to the reduction in the leakage current and oxygen vacancy in the compositions. An interesting correlation between the antiferromagnetic Néel temperature (T
N) of bismuth ferrite and the temperature-dependent dielectric constant is observed in all samples. Bi0.9Ba0.1Fe0.95Gd0.05O3 ceramic possesses maximum coupling between electric dipole and magnetic dipole with an estimated magnetodielectric effect MD ([ε
r(H) − ε
r (0)]/ε
r (0)) ∼ 380 at an applied field of 6 kOe. Impedance spectroscopy in the frequency range 40–107 Hz and temperature within 30–300 °C suggests that grain relaxation is dominant in the samples. Electrical parameters (such as capacitance and resistance) of the grains are determined using the real and imaginary parts of impedance (Z′ and Z″) and the electrical modulus (M′ and M″) plot. The results of electrical conductivity indicate a correlated barrier hopping conduction mechanism in the samples.
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