Magnetoelectric biferroic nanocomposite with composition 0.5Ni 0.5Zn 0.5Fe 2O 4 + 0.5BaTiO 3 was synthesized by ceramic technique. The structural and electrical characterizations of the investigated nanocomposite are discussed and reported. The formation of nanosized composite with two separate phases was confirmed by X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The variation of dielectric constant (ε'), dielectric loss factor (ε") and the ac conductivity (σac) of 0.5Ni 0.5Zn 0.5Fe 2O 4 + 0.5BaTiO 3 was investigated as a function of both frequency and temperature. Thermal hysteresis (first-order transition) was obtained during heating (300 - 830 K) and cooling runs (830 - 300 K). The exact transition temperature and the amount area of the thermal hysteresis depend on applied ac electric field. The delay (lagging) time between heating and cooling processes was esti-mated from the hysteresis loop area versus frequency. The conduction mechanism in the investigated samples was explained according to different models. This study enhances the use of this prepared system in memory applications.
Ferroic materials are those which display spontaneous magnetization (ferromagnetic), polarization (ferroelectric) and strain (ferroelastic). Materials that possess two “ferro” properties simultaneously are called “biferroics”. There are three kinds of biferroic materials namely, Electroelastic, Magnetoelastic and Magnetoelectric materials [
In this work, Nickel zinc ferrite-Barium titanate biferroic nanocomposite system (0.5Ni0.5Zn0.5Fe2O4 + 0.5BaTiO3) was synthesized by standard double sintering technique [
The crystal structure of the prepared nanocomposite and their constituent phases were determined by X-ray diffractometer model Proker D8 with CuKa radiation (l = 1.5418 Å) in a wide range of Bragg’s angle (2q) ranging from (20˚ - 80˚) at room temperature. The average particle size (L) was calculated from X-ray line broadening using (311) peak and Debye-Sherrer’s equation [
The XRD patterns of 0.5Ni0.5Zn0.5Fe2O4 + 0.5BaTiO3 ME nanocomposites is shown in
The typical SEM micrograph is shown in
Fourier Transform Infrared Spectroscopy (FT-IR) spectra,
Zn2+ prefers tetrahedral sites because of its facility to form covalent bonds involving sp3 hybrid orbitals. The ν1 band observed at ~579 cm–1 can be assigned to the stretching vibration of (Fe3+ + O2− ) on tetrahedral site and the ν2 band observed at ~420 cm–1, involves the stretching vibration of (Fe3+ + O2− ) on the octahedral site. These results are in agreement with that published earlier [
The variation of the dielectric constant with frequency reveals dispersion due to Maxwell-Wagner type interfacial polarization which is in good agreement with Koop’s phenomenological theory [
Figures 5(a)-(c) correlate the real part of dielectric constant (ε') and absolute temperature during heating and cooling runs, in the temperature range (from R.T ↔ 830 K) at selected frequencies for the composite 0.5Ni0.5Zn0.5Fe2O4 + 0.5BaTiO3. These curves indicate that, the: 0.5Ni0.5Zn0.5Fe2O4 + 0.5BaTiO3 nano-composite posses a thermal hysteresis loop behavior which could be attributed to a first-order transition [
With gradual cooling from 830 K down to the 300 K, the cooling curve did not overlap on the heating one due to the relaxation process. The interesting features of the dielectric constant versus temperature diagram are the following: the cooling curve lies above the heating one and they do not merge to each other. This indicates that the cooling process could cause a substantial increase in the dielectric constant due to the increase in the density of the dipole moments towards the transition from paraelectric to ferroelectric nature. The dielectric constant of ferroelectric materials is extremely high near the transition temperature, the polarization induced in the paraelectric (non polar) region at T > Tc by an applied electric field along the ferroelectric axis goes gradually over into the spontaneous polarization region upon cooling below Tc. The effect of this field tends to shift Tc to a higher temperature [
On drawing the calculated values of the area of the loop versus frequency
where y represents the hysteresis loop area, y0 is the area at zero frequency, A1 and A2 are constants, x represents the applied frequency and t1, t2 are the reciprocal of relaxation (life) times. The calculated values of t1 and t2 are 1.48 × 105 and 1.2 × 106 Hz respectively. Time dependent dielectric constant measurements reveal memory effects of the investigated composite [
The area between the two curves can be attributed to the heat dissipation due to the friction between the dipoles. The behavior of the area between the two curves versus frequency has the same trend as that of the real part of the dielectric constant versus frequency in the same temperature range.
The conduction mechanisms in ferrite and piezoelectric phases are separately attributed to the Verwey-de Boer model [
where A is constant, while the exponent (s) is very important which determine the dominant type of conduction mechanisms. According to the quantum mechanical tunneling (QMT) model [
It is illustrated from
The calculated values of the power (s) of Equation (2) were derived from lnσac versus ln(ω) plots,
The variation of Seebeck coefficient (α) with temperature (T) is shown in
Biferroic magnetoelectric nanocomposite 1:1 in weight consisting of BaTiO3 as a ferroelectric phase and Ni0.5Zn0.5Fe2O4 as a ferrite phase was prepared by conventional ceramic method. XRD patterns reveal the presence of both ferrite and ferroelectric phases without any intermediate phases. The ac conductivity measurements and Seebeck coefficient suggest that the conduction is due to small polaron hopping and quantum mechanical tunneling mechanisms. Dielectric constant, dielectric loss factor and ac conductivity of the investigated composite show thermal hysteresis (first-order transition) behavior when the experimental data were collected during heating (300 - 830 K) and cooling (830 - 300 K) processes. The area of the hysteresis loop is frequency dependent. The investigated Biferroic system can be used in memory applications.
The authors acknowledge Prof. Dr. N. Okasha and Dr. S.I. El-Dek for great support and for their help in discussions.