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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]

(1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xBiFeO3 (0 ≤ x ≤0.9) ternary ceramics were prepared by the modified Pechini method. X ray diffraction patterns manifest that the samples undergo a gradual structural transformation from the rhombohedral-tetragonal morphotropic phase boundary to the rhombohedral phase with the increasing content of BiFeO3. Room temperature ferromagnetism was observed in BiFeO3-rich samples with x ≥ 0.6, and this ferromagnetism can be ascribed to the suppression of the spiral spin structure with the canting of antiferromagnetically ordered spins. The BiFeO3-rich samples (x=0.6-0.8) exhibit superior ferroelectric properties with the maximum remanent polarization of 44.7 lC/cm², as confirmed by the positive-up negative-down measurement to exclude the contribution of leakage current. The coexistence of room-temperature ferromagnetism and ferroelectricity manifests that the lead-free BiFeO3-based solid solutions are quite promising multiferroic materials and may be important for potential applications in BFO-based magnetoelectric devices. [ABSTRACT FROM AUTHOR]

We report the detailed investigations of the magnetic properties, electronic transport, and specific heat in Zn-doped antiperovskite compounds Ga1-xZnxCMn3. Magnetic measurements indicate the metastability of the antiferromagnetic (AFM)-ferromagnetic intermediate (FI) phase transition and the coexistence of different magnetic phases at lower temperature. The enhanced giant magnetoresistance (GMR) is observed with a maximum value of 70% spanning a temperature range of 100 K at 50 kOe. The analysis of heat capacity reveals that the metastability of the AFM-FI transition and the enhanced GMR observed in Ga1-xZnxCMn3 may originate from the reconstruction of Fermi surface accompanying AFM-FI transition. [ABSTRACT FROM AUTHOR]

We report an enhanced negative giant magnetoresistance (GMR) with larger temperature span in Ni-doped antipervoskite compounds GaCMn3-xNix. The observed GMR can peak at ∼75% (at 85 kOe) and exceed 60% (at 50 kOe) over a temperature span of approximate 110 and 50K for x=0.05 and 0.10, respectively. Compared with the parent GaCMn3, the well-enhanced GMR in Ni-doped samples is suggested to be associated with the partially suppressed antiferromagnetic (AFM) ground state, which favors the transition from the high-resistivity AFM state to the low-resistivity canted ferromagnetic state under an external magnetic field. [ABSTRACT FROM AUTHOR]

The magnetic and dielectric properties of Bi6Fe2Ti3O18, Bi6FeCoTi3O18, and Bi5LaFeCoTi3O18 are investigated. The room-temperature ferromagnetism is observed in the samples Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 compared with the paramagnetic behavior in Bi6Fe2Ti3O18 at room temperature. The ferromagnetism in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 can be ascribed to spin canting of the Fe-based and Co-based sublattices via the antisymmetric Dzyaloshinskii-Moriya interaction. The frequency-dependent behavior of the dielectric loss peak in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 manifests itself a thermally activated relaxation process. The rather large activation energy (2.62 ± 0.11 eV for Bi6FeCoTi3O18 and 1.97 ± 0.07 eV for Bi5LaFeCoTi3O18) implies that the relaxation process is not due to the thermal motion of oxygen vacancies inside ceramics. [ABSTRACT FROM AUTHOR]