Browsing by Author "Wang, Naigang"
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- Destruction of spin cycloid in (111)(c)-oriented BiFeO3 thin films by epitiaxial constraint: Enhanced polarization and release of latent magnetizationBai, Feiming; Wang, Junling; Wuttig, Manfred; Li, Jiefang; Wang, Naigang; Pyatakov, Alexander P.; Zvezdin, Anatoly Konstantinovich; Cross, L. E.; Viehland, Dwight D. (AIP Publishing, 2005-01-01)In BiFeO3 films, it has been found that epitaxial constraint results in the destruction of a space modulated spin structure. For (111)c films, relative to corresponding bulk crystals, it is shown (i) that the induced magnetization is enhanced at low applied fields; (ii) that the polarization is dramatically enhanced; whereas, (iii) the lattice structure for (111)(c) films and crystals is nearly identical. Our results evidence that eptiaxial constraint induces a transition between cycloidal and homogeneous anti ferromagnetic spin states, releasing a latent antiferromagnetic component locked within the cycloid. (C) 2005 American Institute of Physics.
- Dramatically enhanced polarization in (001), (101), and (111) BiFeO3 thin films due to epitiaxial-induced transitionsLi, Jiefang; Wang, Junling; Wuttig, Manfred; Ramesh, R.; Wang, Naigang; Ruette, Benjamin; Pyatakov, Alexander P.; Zvezdin, Anatoly Konstantinovich; Viehland, Dwight D. (AIP Publishing, 2004-06-01)Dramatically enhanced polarization has been found for (001), (101), and (111) films, relative to that of BiFeO3 crystals. The easy axis of spontaneous polarization lies close to (111), for the various oriented films. BiFeO3 films grown on (111) have a rhombohedral structure, identical to that of single crystals; whereas films grown on (101) or (001) are monoclinically distorted from the rhombohedral structure, due to the epitaxial constraint. (C) 2004 American Institute of Physics.
- Fe-Ga/Pb(Mg1/3Nb2/3)O-3-PbTiO3 magnetoelectric laminate compositesDong, Shuxiang; Zhai, Junyi; Wang, Naigang; Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Lograsso, Thomas A. (AIP Publishing, 2005-11-01)We have found large magnetoelectric (ME) effects in long-type laminate composites of Fe-20% Ga magnetostrictive alloys and piezoelectric Pb(Mg1/3Nb2/3)O-3-PbTiO3 single crystals. At lower frequencies, the ME voltage coefficient of a laminate with longitudinally magnetized and longitudinally polarized (i.e., L-L mode) layers was 1.41 V/Oe (or 1.01 V/cm Oe). Near the natural resonant frequency (similar to 91 kHz) of the laminate, the ME voltage coefficients were found to be dramatically increased to 50.7 V/Oe (36.2 V/cm Oe) for the L-L mode. In addition, the laminate can detect a minute magnetic field as low as similar to 2 x 10(-12) T at resonance frequency, and similar to 1 x 10(-10) T at lower frequencies. (c) 2005 American Institute of Physics.
- Intermediate ferroelectric orthorhombic and monoclinic M-B phases in [110] electric-field-cooled Pb(Mg1/3Nb2/3)O-3-30%PbTiO3 crystalsCao, Hu; Bai, Feiming; Wang, Naigang; Li, Jiefang; Viehland, Dwight D.; Xu, Guangyong; Shirane, Gen (American Physical Society, 2005-08-01)Structural phase transformations of [110] electric-field-cooled Pb(Mg1/3Nb2/3)O-3-30%PbTiO3 (PMN-30%PT) crystals have been performed by x-ray diffraction. A phase sequence of cubic (C)-> tetragonal (T)-> orthorhombic (O)-> monoclinic (M-B) was found on field cooling (FC); and a rhombohedral (R)-> M-B-> O sequence was observed with increasing field, beginning from the zero-field-cooled condition at room temperature. The application of the [110] electric field induced a dramatic change in the phase sequence in the FC condition, compared to the corresponding data for PMN-30%PT crystals in a [001] field, which shows that the phase sequence in the FC condition is altered by the crystallographic direction along which a modest electric field (E) is applied. Only when E is applied along [110] are intermediate O and M-B phases observed.
- Multiferroic Bismuth Ferrite-Lead Titanate and Iron-Gallium Crystalline Solutions: Structure-Property InvestigationsWang, Naigang (Virginia Tech, 2005-05-17)Recently, multiferroics-defined as materials with coexistence of at least two of the ferroelectric, ferroelastic and ferromagnetic effects-have attracted enormous research activities. In this thesis, the structure and properties of multiferrioic BiFeO3-x%PbTiO3 and Fe-x%Ga crystalline solutions were investigated. First, the results show that modified BiFeO3-PbTiO3 based ceramics have significantly enhanced multiferroic properties, relative to BiFeO3 single crystals. The data reveal: (i) a dramatic increase in the induced polarization; and (ii) the establishment of a remnant magnetization by a breaking of the translational invariance of a long-period cycloidal spin structure, via substituent effects. In addition, temperature dependent magnetic permeability investigations of BiFeO3-xPbTiO3 crystalline solutions have shown that aliovalent La substitution results in a significant increase in the permeability. Second, room temperature high-resolution neutron and x-ray diffraction studies have been performed on Fe-x%Ga crystals for 12
- Multiferroic properties of modified BiFeO3-PbTiO3-based ceramics: Random-field induced release of latent magnetization and polarizationWang, Naigang; Cheng, J.; Pyatakov, Alexander P.; Zvezdin, Anatoly Konstantinovich; Li, Jiefang; Cross, L. E.; Viehland, Dwight D. (American Physical Society, 2005-09-28)It has been found that aliovalent-substituted BiFeO3-PbTiO3-based polycrystalline materials have significantly enhanced multiferroic properties. Relative to unmodified BiFeO3, our results for modified BiFeO3-PbTiO3-based ceramics reveal: (i) a dramatic increase in the electric-field-induced polarization; and (ii) the establishment of a remanent magnetization. The results evidence the destruction of a space-modulated spin structure in bulk materials, via substituent effects, releasing a latent magnetization locked within the cycloid.
- A small, linear, piezoelectric ultrasonic cryomotorDong, Shuxiang; Yan, Li; Wang, Naigang; Viehland, Dwight D.; Jiang, Xiaoning; Rehrig, P.; Hackenberger, Wesley S. (AIP Publishing, 2005-01-01)A small, linear-type, piezoelectric ultrasonic cryomotor has been developed for precision positioning at extremely low temperatures (greater than or equal to-200 degreesC). This cryornotor consists of a pair of Pb(Mgl(1/3)Nb(2/3))O-3-PbTiO3 single crystal stacks, which are piezoelectrically excited into the rotating third-bending mode of the cryomotor stator's center, which in turn drives a contacted slider into linear motion via frictional forces. The performance characteristics achieved by the cryornotor are: (i) a maximum linear speed of >50 mm/s; (ii) a stroke of >10 mm; (iii) a driving force of >0.2 N; (iv) a response time of similar to29 ms; and (v) a step resolution of similar to20 nm. (C) 2005 American Institute of Physics.
- X-ray and neutron diffraction investigations of the structural phase transformation sequence under electric field in 0.7Pb(Mg1/3Nb2/3)-0.3PbTiO(3) crystalBai, Feiming; Wang, Naigang; Li, Jiefang; Viehland, Dwight D.; Gehring, Peter M.; Xu, Guangyong; Shirane, Gen (American Institute of Physics, 2004-08-01)The structural phase transformations of 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) (PMN-30%PT) have been studied using x-ray diffraction (XRD) and neutron scattering as a function of temperature and electric field. We observe the phase transformational sequence (i) cubic (C)--> tetragonal (T)--> rhombohedral (R) in the zero-field-cooled (ZFC) condition; (ii) C-->T--> monoclinic (M-C)--> monoclinic (M-A) in the field-cooled (FC) condition; and (iii) R-->M-A-->M-C-->T with increasing field at fixed temperature beginning from the ZFC condition. Upon removal of the field, the M-A phase is stable at room temperature in the FC condition, and also in the ZFC condition with increasing field. Several subtleties of our findings are discussed based on results from thermal expansion and dielectric measurements, including (i) the stability of the M-A phase, (ii) a difference in lattice parameters between inside bulk and outside layer regions, and (iii) a difference in the phase transition temperature between XRD and dielectric data. (C) 2004 American Institute of Physics.