Simultaneous enhancement of magnetic and ferroelectric properties of LaFeO3 by co-doping with Dy3+ and Ti4+

Abstract

To improve the magnetic and ferroelectric behavior of LaFeO3 (LFO), co-doping with Dy3+ and Ti4+ are considered and structural, magnetic, dielectric and ferroelectric properties are investigated. Samples of LFO and La(1-x)DyxFe(1-y)TiyO3 (for x/y = 0.02, LDFTO1; 0.04, LDFTO2 and 0.1, LDFTO) are prepared by conventional solid state reaction method. Here we have chosen two ions of Dy3+ and Ti4+ as dopants where the first one can enhance the magnetic moment as its free ion magnetic moment is quite high and the second one may enhance the ferroelectric component through structural and/or charge misbalance. The crystallographic phase of each sample is confirmed by analyzing the X-ray diffraction pattern (XRD) recorded at room temperature (RT) by Rietveld method using MAUD program. Rietveld analyses of LFO, LDFTO1, LDFTO2 and LDFTO reveals that a compressive lattice distortion is induced due to the co-substitution of Dy3+ and Ti4+ ions at the A and B sites, respectively. Though Rietveld analyses of the XRD patterns of all the doped samples confirmed the solubility of the dopants in the host lattice of LFO but dielectric and ferroelectric response of LDFTO1 and LDFTO2 is quite poor compared to that of LDFTO. Due to this fact the detailed investigations are carried out for LDFTO, only. Raman spectra of LFO and LDFTO recorded at RT and the observed data are analyzed to extract different useful information. Hysteresis loops of LFO and LDFTO recorded at 300 and 5 K in vibration sample magnetometer show enhanced magnetization of LDFTO compared to that of LFO. The magnetization vs. temperature recorded under zero field cooled (ZFC) and field cooled (FC) conditions exhibit an antiferromagnetic to ferromagnetic phase transition below ∼85 K which is attributed to the substitution of Dy3+ ions in LFO. Dielectric properties in the temperature range of 300–900 K of LFO and LDFTO measured in the frequency range of 1 KHz-5 MHz revealed that the value of dielectric constant (ε′) increases and the dielectric loss (tanδ) decreases compared to that of LFO. This suggests that the resistivity of the co-doped sample increases and conductivity decreases. The thermal variation of dielectric constant clearly indicate a transition from ferroelectric to paraelectric phase at and above ∼670 K. Polarization vs. electric field (P-E) loops for both the samples of LFO and LDFTO recorded at 300 K clearly indicates that the PE loops of LDFTO are quite impressive compared to that of LFO.