Dielectric relaxation and magnetic properties of Cr doped GaFeO₃

Abstract

Polycrystalline GaFe 1-x Cr x O 3 (x= 0.05, 0.1 and 0.15) samples were prepared by solid state reaction. The monophasic compounds crystallize in the orthorhombic space group P c 2 1 n and the unit cell volume decreases with increasing Cr content. The saturated magnetization and magnetic transition temperature of the ceramics decrease due to the dilution of the magnetic interaction with Cr concentration. The dielectric properties were investigated from 133 to 353 K at various frequencies (100-10 7 Hz). Whereas the dielectric constant decreases with Cr-content an increase of dielectric loss tangent was observed. The activation energy of the compounds (calculated both from loss and modulus spectrum) are the same and have values~0.22 and 0.27 eV for Cr=10 and 15%, respectively, and hence the relaxation process may be attributed to the same type of charge carrier. A separation of the grain and grain boundary properties has been achieved using an equivalent circuit model. The capacitance and resistances associated with the grain boundary were found to be higher than that associated with grain. IntroductionThe study of multiferroics is a very hot topic. It is interesting not only from the point of view of fundamental physics but also for many potential applications in electronics [1,2].GaFeO 3 has an orthorhombic crystal structure (space group P c 2 1 n) with four different cation sites labeled Ga1, Ga2 (mostly occupied by gallium) and Fe1, Fe2 (mostly occupied by iron). This material has a spontaneous polarization along the b axis and a ferrimagnetic structure below room temperature result from unequal distribution of Fe spins of nearly equal magnitude on the sublattices with a magnetic moment of the spin along the c axis [3,4].GaFeO 3 contains only trivalent metals in the structure like rare earth orthoferrites, making them attractive systems for investigations of isovalent substitutions. In particular, the replacement of Fe 3+ by Cr 3+ and its effect on structural, magnetic and other properties have been reported [5][6][7] for rare earth orthoferrites. For example, in the lanthanum orthoferrites, partial replacement of Fe by Cr leads to a reduction in the Néel temperature from 750 K in LaFeO 3 to 280 K in LaCrO 3 . Moreover, Cr doping is one of the most adopted strategies to tailor the dielectric and piezoelectric properties of ferroelectrics for practical applications. It is well known that Cr is effective in decreasing the aging effect and the dielectric loss; thus, the effect of doping of Cr 3+ is that of a stabilizer of the piezoelectric and dielectric properties [8,9].In the present work we study the (a) magnetic properties, (b) apply the variablefrequency technique of impedance spectroscopy to the samples over a wide temperature range, and (c) characterize the grain and grain boundary resistance using IS, from which one can calculate their capacitance and can model the equivalent circuit for Cr-substituted GaFeO 3 samples.

Influence of Cr substitution on structural, magnetic and electrical conductivity spectra of LaFeO3

“…the activation energy were 0.61 eV, an oxygen vacancy and 0.24 eV, similar activation energy is reported for GaFe 0.9 Cr 0.1 O 3[57]. The region I of LaFe 0.7 Cr 0.3 O 3 and LaFe 0.5 Cr 0 5.…”

Dielectric behaviors of Aurivillius Bi5Ti3Fe0.5Cr0.5O15 multiferroic polycrystals: Determining the intrinsic magnetoelectric responses by impedance spectroscopy

“…Two poorly resolved semicircular arcs at 380 K can clearly be distinguished as illustrated in Fig. 6(a), which are usually ascribed to the contributions of grains (G) and grain boundaries (GB), respectively142030. Clearly, the radius of the low-frequency semicircle is much larger than that of the high-frequency one, reflecting the large difference in magnitudes of resistance between G and GB.…”

“…Especially, the multi-valence configuration of Ni, Mn, Fe, Cr and Co cations would bring about creation of plausible electrical heterogeneities142627282930. Accordingly, polarizability along with conductivity simultaneously occur when these multi-valence cations are included in oxides, where electron/hole migration between the mixed valence states is usually involved, which plays a predominant role in determining the electrical properties.…”

Enhanced photocatalytic activity of transition metal ions Mn2+, Ni2+ and Zn2+ doped polycrystalline titania for the degradation of Aniline Blue under UV/solar light

“…Hence the space charge region becomes narrow and the penetration depth of light into TiO 2 greatly exceeds the thickness of the space charge layer which increases the recombination rate of electrons and holes. Moreover, at a high dopant concentration, the charge carriers may be trapped more than once on its way to the surface so that their mobility becomes extremely low and undergoes recombination before it can reach the surface [75,79]. In addition at higher concentrations, these trap centers are close to one another and the trapped charge carriers can recombine through quantum tunneling, the probability of which increases with increase in the dopant concentration.…”