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Single-phase polycrystalline SrBi5Ti4CrO18 and SrBi5Ti4Cr0.5Co0.5O18 were synthesized by a modified Pechini method. Both samples have an orthorhombic structure with the space group B2cb. The valence state of Cr is suggested to be +3 and the Co ions exist in the form of Co2+ and Co3+ based on the results of x-ray photoelectron spectroscopy. The sample SrBi5Ti4Cr0.5Co0.5O18 exhibits the paramagnetic state, whereas SrBi5Ti4Cr0.5Co0.5O18 undergoes a ferrimagnetic transition at 89K originating from the antiferromagnetic coupling of Cr-based and Co-based sublattices. In addition, SrBi5Ti4Cr0.5Co0.5O18 shows a typical spin-glass behavior below 89K with zν =6.02 and τ0=(1.75±0.33)x10-14 s as evidenced by the results of the frequency dependence of ac susceptibility and magnetic relaxation measurements. In particular, both the dielectric constant and dielectric loss of SrBi5Ti4Cr0.5Co0.5O18 exhibit the characteristics of dielectric relaxation around 89K with the activation energy of (0.14±0.02) eV, which can be ascribed to the electron hopping of Co2+-VO-Co3+ through the bridging oxygen vacancies. [ABSTRACT FROM AUTHOR]

We investigate the structural, magnetic, dielectric properties, and scaling behaviors of Aurivillius compounds Bi6-x/3Fe2Ti3-2x(WCo)xO18 (0 ⩽ x ⩽ 0.15). The room-temperature weak ferromagnetism is observed for the W/Co co-doped samples. The results of the dielectric constant εr, complex impedance Z", the dc conductivity σdc, and hopping frequency fH manifest that the dielectric relaxation of the x = 0 sample and the doped samples in the dielectric anomaly region (450-750 K) can be ascribed to the trap-controlled ac conduction around the doubly ionized oxygen vacancies and the localized hopping process of oxygen vacancies, respectively. The scaling behaviors reveal that the dynamic process of both electrons in the x = 0 sample and oxygen vacancies in the doped samples is temperature independent. The ferroelectric Curie-temperature Tc decreases slightly from 973K to 947K with increasing the doping level of W/Co. In addition, the dielectric loss exhibits a dielectric relaxation above 800K with the rather large activation energies (1.95 eV ⩽ Ea ⩽ 2.72 eV). [ABSTRACT FROM AUTHOR]

We investigate the magnetic, dielectric, and magnetodielectric properties of rare-earth-substituted Aurivillius phase Bi6Fe1.4Co0.6Ti3O18. The room-temperature ferromagnetic behavior is observed in all samples, and the rare-earth-substituted samples exhibit an enhanced magnetization. The weak ferromagnetism can be ascribed to the spin canting of the antiferromagnetic coupling of the Fe-based and Co-based sublattices via Dzyaloshinsky-Moriya interaction. The dielectric loss of all samples exhibits two dielectric relaxation peaks corresponding to two different relaxation mechanisms. One relaxation process with Ea = 0.5 eV is related to the hoping process of oxygen vacancies and the other one with Ea = 1.6 eV can be ascribed to the intrinsic conduction. The Gd-doped sample exhibits a remarkable magnetodielectric effect (9.4%) at RT implying this Aurivillius phase may be the potential candidate for magnetodielectric applications. [ABSTRACT FROM AUTHOR]

We investigate the structural, magnetic, and electrical properties of charge-spin co-doped Ba1-x-yLax+yTi1-xMxO3 (M = Cr, Fe, and Co). For Ba1-x-yLax+yTi1-xCrxO3, carrier doping induces short-range ferromagnetism, and we find a large negative magnetoresistance in these compounds. However, for Ba1-x-yLax+yTi1-xMxO3 (M = Fe and Co), the magnetism does not seem to couple with the charge carriers. The transport properties of Ba1-x-yLax+yTi1-xCrxO3 can be described by a three-dimensional variable-range-hopping model that implies itinerant charge carriers, whereas almost all the samples of Ba1-x-yLax+yTi1-xMxO3 (M = Fe and Co) exhibit high resistivity. It is known that only the itinerant charge carriers can enhance the coupling of two isolated magnetic ions. Therefore, there is almost no long-range ferromagnetism in the studied system. [ABSTRACT FROM AUTHOR]

We present our investigation on the critical behavior of the spinel compound CdCr2S4 via the ac susceptibility and dc magnetization measurements. The analysis of ac susceptibility in terms of scaling behavior yields exponent values of δ=5.38±0.01, γ+β=1.77±0.03 and γ=1.44±0.02. Both δ and γ are slightly larger than that predicted by Heisenberg model. Detailed analyses of the inverse of the susceptibility and the electron spin resonance experiment reveal that the existence of correlated magnetic polarons has a key impact on the ferromagnetism of the spinel CdCr2S4. The abnormal critical exponent value of δ of CdCr2S4 may be attributed to the formation of the correlated magnetic polarons and abnormal spin-phonon coupling. [ABSTRACT FROM AUTHOR]

We present the results of a systematic study of the transport mechanism and magnetothermoelectric power (MTEP) of electron-doped manganites La0.85Te0.15Mn1-xCuxO3 (0<=x<=0.20). Two peaks are observed in thermoelectric power S(T) curves for x<0.10 samples. For x>0.10 samples, the very large S value with over 100 μV/K at low temperatures appears, which is attributed to the destruction of ferromagnetic (FM) order and the strong carrier localization at low temperatures due to Cu doping. In addition, a sign variation of S(T) for Cu-doped samples is also observed, which may originate from the narrowing of the concomitant σ(eg↑-2p) band. Particularly, an anomalous behavior of S(T) is observed in x=0.10 sample, which is suggested to be related to the contribution of spin polarization and phonon drag. Based on the results of resistivity ρ(T) and S(T), the transport mechanism in the high-temperature paramagnetic region for all the samples and low-temperature FM insulating region below TC for the samples with x<=0.10 can be described by the variable-range-hopping model. However, in the intermediate-temperature FM metallic region below TC, ρ(T) and S(T) of the samples with x<=0.10 are well fitted by the formula ρ=ρ0+ρ2.5T2.5 and S=S0+S3/2T3/2+S4T4, respectively, implying the importance of electron-magnon scattering. As to the MTEP, only a negative MTEP peak close to TC is observed in the whole measured temperature range for the samples with x>0.10, which is suggested to originate from the spin alignment induced by applied magnetic fields. However, for x<=0.10 samples, an additional positive MTEP peak is induced by Cu doping below TC besides a large negative MTEP peak in the vicinity of TC, which is ascribed to the enhancement of electron-magnon interaction caused by the Cu doping and the decrease of magnetic entropy around TC, respectively. [ABSTRACT FROM AUTHOR]