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We report a quantum paraelectric (QP) to dipolar glass (DG) phase transition induced by Sc substitution in ferrimagnetic hexaferrite BaFe 12 − x Sc x O 19 (0 ≤ x ≤ 2.4) single crystals. The DG behavior is revealed via anisotropic dielectric spectroscopy, polarization, and specific heat measurements. The phase evolution from QP to DG (0.5 ≤ x ≤ 1.2) and finally to the nonpolar state (x ≥ 2.4) with increasing x is found to be due to the competition between the enhanced polar instability by lattice volume expansion and disordered/frustrated dipole-dipole interaction induced by the partial replacement of Sc 3 + for Fe 3 + in the bipyramids. Our results suggest further experimental clues to realize possible multiferroicity with strong displacive ferroelectricity in BaFe 12 O 19 and other magnetic materials. [ABSTRACT FROM AUTHOR]

We investigate the effect of Jahn-Teller (JT) active Cu2+ ions on the structural, magnetic, and ferroelectric properties of Co1–xCuxCr2O4 (0 ≤ x ≤ 0.4). All the samples can be indexed with a cubic lattice with space group Fd 3 ¯ m at room temperature. All the samples undergo a paramagnetic-ferrimagnetic transition at TC and spiral ferrimagnetic ordering at TS. The magnetization measurements manifest that magnetization reversal occurs in the x = 0.2 and 0.3 samples. The x = 0.3 sample possesses a rather large polarization of 14 μC/m2, which is 7 times in magnitude compared with the CoCr2O4 single crystal. The analysis of the infrared active phonon modes implies that two T 1 u (IR) optical phonon modes are gradually split into a doublet at around 40 K, implying the lowering of lattice symmetry. The presence of a low-symmetry tetragonal phase becomes polar and enhances the electric polarization of Co0.7Cu0.3Cr2O4. [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]

The structural, magnetic, and dielectric properties of the YCr0.88Fe0.12O3 single crystals were studied. Detailed magnetic studies demonstrate that the crystal is antiferromagnetic with weak canted ferromagnetism and experiences three sequential magnetic transitions around TN1~127.3K, TN2~115.2 K, and TSR~99.0 K. Interestingly, a temperature induced spin reorientation (SR) near TSR and magnetic field induced SR below TSR were observed. The H-T phase diagram was revealed to be quite different from both parent compounds YFeO3 and YCrO3. A dielectric relaxation around TN1 was found to be associated with electron hopping. An intrinsic magnetoelectric effect was also observed at low temperatures. These results are helpful for understanding the exotic magnetic and magnetoelectric properties in the orthochromite and orthoferrite related systems. [ABSTRACT FROM AUTHOR]

We have investigated the structural, magnetic, and dielectric properties of RFe0.5Cr0.5O3 (R = Nd, Sm, Gd, and Y) compounds. Both structure and magnetic analyses show a Fe/Cr cation disorder, which results in the existence of Fe-rich and Cr-rich clusters. The competition between the moments of the two clusters gives rise to the R-dependent temperature induced magnetization reversal. Interestingly, we also find that the charge carrier hopping in the two clusters leads to two sequential dielectric relaxations in all the samples. In addition, giant magnetocaloric effect with a magnetic entropy change reaching ~29.2 J/kg K was observed with R = Gd. [ABSTRACT FROM AUTHOR]

We have investigated the detailed magnetic, magnetoelectric (ME), magnetodielectric (MD) and thermal expansion properties in Co4Nb2O9 crystal. A magnetic-field-induced spin flop was observed below antiferromagnetic (AFM) transition temperature TN. Dielectric constant at applied magnetic field nearly diverges around the AFM transition, giving rise to a colossal MD effect as high as ~138% around TN. Theoretical analysis of the ME and MD data revealed a major contribution of critical spin fluctuation to the colossal MD effect in Co4Nb2O9. These results suggest that linear ME materials with large ME coupling might be potentially used to realize large MD effect for future application. [ABSTRACT FROM AUTHOR]

DyFe0.5Cr0.5O3 has been synthesized using a sol-gel method. It exhibits ferroelectricity at the antiferromagnetic ordering temperature TN1 ~ 261K. Large magnetocaloric effect (MCE) (11.3 J/kgK at 4.5 T) enhanced by magnetoelectric coupling due to magnetic field and temperature induced magnetic transition was observed. Temperature-dependent Raman study shows an anomalous behavior near TN1 in the phonon modes related to the vibration of Dy atoms and stretching of CrO6/FeO6 octahedra, suggesting the ferroelectricity in DyFe0.5Cr0.5O3 is associated with the spin-phonon coupling with respect to both Dy and Cr/Fe ions. These results suggest routes to obtain high-temperature multiferroicity and large MCE for practical applications. [ABSTRACT FROM AUTHOR]

DyFe0.5Cr0.5O3 has been synthesized using a sol-gel method. It exhibits ferroelectricity at the antiferromagnetic ordering temperature TN1 ~ 261K. Large magnetocaloric effect (MCE) (11.3 J/kgK at 4.5 T) enhanced by magnetoelectric coupling due to magnetic field and temperature induced magnetic transition was observed. Temperature-dependent Raman study shows an anomalous behavior near TN1 in the phonon modes related to the vibration of Dy atoms and stretching of CrO6/FeO6 octahedra, suggesting the ferroelectricity in DyFe0.5Cr0.5O3 is associated with the spin-phonon coupling with respect to both Dy and Cr/Fe ions. These results suggest routes to obtain high-temperature multiferroicity and large MCE for practical applications. [ABSTRACT FROM AUTHOR]

Large quantities of very thin and wide single-crystal alpha silicon nitride (α-Si[sub 3]N[sub 4]) nanobelts were synthesized by a vapor-solid thermal reaction between ammonia and silicon monoxide (SiO) without using any added catalyst. Scanning electron microscopy, high-resolution electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction were used to characterize the formed nanobelts. The single-crystal α-Si[sub 3]N[sub 4] nanobelts are about 800–1200 nm in width, 20–35 nm in thickness and about several tens to several hundreds of micrometers in length. The nanobelts are perfect in structure. The nanobelts grow along [011] and [100] direction. Intense visible photoluminescence (PL) occurring on the wide and thin nanobelts over a broad spectrum ranging from 420 to 750 nm was observed. The visible PL emission is related to the inherently imperfect Si and N dangling bonds in the α-Si[sub 3]N[sub 4] structure. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetic and ferroelectric properties of Co-doped Bi6Fe2Ti3O18 thin films Bi6Fe2-xCoxTi3O18 (BFCTO) (0 ≤x≤ 1) are investigated. The coexistence of room-temperature ferromagnetism and ferroelectricity is observed in BFCTO thin films. The x = 0.6 sample exhibits a higher remnant magnetization Mr of 8.41 emu/cm3 and a remnant polarization Pr of 17.6 μC/cm2 compared with other BFCTO thin films. The ferromagnetism can be ascribed to the spin canting of Fe- and Co-based sublattices via the Dzyaloshinskii-Moriya interaction [I. Dzyaloshinsky, J. Phys. Chem. Solids 4, 241 (1958); T. Moriya, Phys. Rev. 120, 91 (1960)]. The change in the remnant polarization is discussed in terms of the variation of grain size and oxygen vacancies caused by Co-doping. [ABSTRACT FROM AUTHOR]

We have performed the temperature dependence of resistivity ρ(T) and thermoelectric power S(T) by a series of doping in layered cobaltites Bi2Sr2Co2Oy. For all samples, a metallic ρ(T) behavior and a large temperature-independent S is observed at higher temperatures, while we found a upturning ρ(T) but without corresponding variation of S(T) at lower temperatures. The present results strongly demonstrate the contribution of narrow band. Moreover, the doping could effectively modulate the thermoelectric performance. Especially for Bi2Sr1.9Ca0.1Co2Oy, it may provide an excellent platform to be a promising candidate of thermoelectric materials. [ABSTRACT FROM AUTHOR]

We have performed the temperature dependence of resistivity ρ(T) and thermoelectric power S(T) by a series of doping in layered cobaltites Bi2Sr2Co2Oy. For all samples, a metallic ρ(T) behavior and a large temperature-independent S is observed at higher temperatures, while we found a upturning ρ(T) but without corresponding variation of S(T) at lower temperatures. The present results strongly demonstrate the contribution of narrow band. Moreover, the doping could effectively modulate the thermoelectric performance. Especially for Bi2Sr1.9Ca0.1Co2Oy, it may provide an excellent platform to be a promising candidate of thermoelectric materials. [ABSTRACT FROM AUTHOR]