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ABSTRACT: Employing the graphene sheets (GSs), the electron scattering constants are measured in the high-angle annular dark-field (HAADF) imaging by the scanning transmission electron microscopy. Single scattering is found to be dominant until the layer number of 200, complying with a simple relation of I = Io(1 - e(-tau/lambda)). The discrete layer counting of the GSs enables precise determination of incident depths. This work results values of lambda = 48.2, 61.4, 97.9 and 115.6 nm for 80, 120, 160 and 200 keV electrons, respectively. The uncertainties with the mean free paths and the cross sections are confined to 10 percent. The dependences on the electron beam energy and the collection angle are discussed based on a multislice simulation.
Journal of Nanoscience and Nanotechnology 08/2012; 12(8):6494-8. · 1.56 Impact Factor
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ABSTRACT: Extensive studies of structural and magnetic properties of pure Ni
n
(n=2–21) clusters are carried out
using density functional theory with generalized gradient approximation. A new structural growth pattern is
reported and the icosahedron sequence is not the global minima structures for size n < 16. The evolution
pattern of Ni5–Ni10 clusters is based on square pyramid. For cluster between n = 9 and n = 14,
structures of them are trilayered stacking pattern. Especially for Ni13, it seriously deviates from
icosahedral pattern which was frequently assumed in previous studies. Ni10, Ni13 and Ni14 are
pieces of a double tetrahedron. For cluster size larger than 16, icosahedron based configurations are found to
be the dominative structure pattern with exception of Ni19. But trilayered structure is a strong
competitor due to small difference in energy between this pattern and icosahedral family. The comparison of
magnetic behavior between the calculations and experimental results are conducted. The average coordination
mainly dominates on the magnetic behavior in the size range we considered.
The European Physical Journal D 04/2012; 61(2):389-396. · 1.48 Impact Factor
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Integrated Ferroelectrics 10/2011; 87(2007):33-41. · 0.30 Impact Factor
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ABSTRACT: We investigate the effect of Al-doping on the multiferroicity of DyMn1−xAlxO3. It is indicated that a slight doping (0.005 ≤ x ≤ 0.01) can significantly enhance the electric polarization which will be suppressed as x>0.03. The possible mechanism for the polarization enhancement is the rearrangement of the Mn spiral spin order upon the Al-doping. Our work demonstrates that the ferroelectricity of DyMnO3 is sensitive to the B-site nonmagnetic doping, allowing an unusual enhancement of the electric polarization.
Applied Physics Letters 06/2010; 96(25):252902-252902-3. · 3.84 Impact Factor
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ABSTRACT: A series of polycrystalline pyrochlore rare-earth titanate Ho2−xCrxTi2O7 are synthesized in order to enhance the ferroelectricity of pyrochlore Ho2Ti2O7. A giant enhancement of polarization P from 0.54 μC/m2 at x = 0 up to ∼ 660 μC/m2 at x = 0.4 is obtained, accompanied with an increment of ferroelectric transition point Tc from Tc ∼ 60 K up to Tc ∼ 140 K. A magnetic anomaly at Tc ∼ 140 K together with the polarization response to magnetic field is identified, implying the multiferroic effect in Ho2−xCrxTi2O7.
Applied Physics Letters 06/2010; 96(24):242904-242904-3. · 3.84 Impact Factor
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ABSTRACT: Hydrogen molecules adsorption and storage in Sc coated Si@Al(12) cluster were investigated using density functional theory methods. Scandium atoms can bind strongly to the surfaces of Si@Al(12) due to the charge transfer between Sc and Si@Al(12), and do not suffer from clustering on the substrate. Si@Al(12) cluster coated with three and four Sc atoms can adsorb 16 and 18 H(2) molecules with a binding energy of 0.28-0.63 eV/H(2), corresponding to hydrogen storage capacity of 6.0 and 6.3 wt %, respectively. The stable Si@Al(12) can be applied as one of candidates for hydrogen storage materials at ambient conditions.
The Journal of chemical physics 06/2010; 132(22):224308. · 3.09 Impact Factor
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ABSTRACT: A series of polycrystalline pyrochlore rare-earth titanate Ho_{2-x}Cr_xTi_2O_7 are synthesized in order to enhance the ferroelectricity of pyrochlore Ho2Ti2O7. For the sample close to the doping level x=0.4, a giant enhancement of polarization P up to 660\muC/m2 from 0.54\muC/m2 at x=0 is obtained, accompanied with an increment of ferroelectric transition point Tc up to ~140K from ~60K. A magnetic anomaly at T~140K together with the polarization response to magnetic field, is identified, implying the multiferroic effect in Ho2-xCrxTi2O7. Comment: 12 pages, 3 figures
03/2010;
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ABSTRACT: Rare-earth titanate cubic pyrochlore Ho <sub>2</sub> Ti <sub>2</sub> O <sub>7</sub> ceramics are prepared by the standard solid state reaction. The magnetic, dielectric, and ferroelectric behaviors are measured in order to investigate the multiferroic behaviors of Ho <sub>2</sub> Ti <sub>2</sub> O <sub>7</sub> . Upon the gradual spin ordering sequence with decreasing temperature, a ferroelectric transition with a small polarization is identified. We discuss the origin of ferroelectricity and its possible correlation with the spin order at low temperature.
Journal of Applied Physics 12/2009; · 2.17 Impact Factor
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ABSTRACT: The studies on the structure and electronic properties of hydrogenated metal embedded Al(12) cage clusters have been performed by density functional theory calculations. We have investigated aluminum cluster hydrides with 12 and 14 hydrogen atoms, respectively. Insertion of the Mg, Ca alkali metals remarkably enhances the stability of the aluminum clusters. The hydrogen atom prefers to occupy on-top sites along the surface of the clusters. Mulliken population analysis indicates that significant charge transfer occurs between the Mg and Ca atoms and the Al atoms. Our computations suggest that these clusters appear to be physically and chemically stable.
The Journal of chemical physics 07/2008; 128(22):224707. · 3.09 Impact Factor
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ABSTRACT: Bi5Ti3FeO15 bulk ceramic and thin film samples are prepared using the sol-gel method. The dielectric, ferroelectric, and magnetic behaviors of these samples are measured in order to investigate the possible multiferroic effect. The superparamagnetic behavior with dominant antiferromagnetic (AFM) interaction background for the as-prepared Bi5Ti3FeO15 samples is revealed. The clearly identified magnetocapacitance effect at low temperature is argued to originate from the suppression of the AFM interaction by external magnetic field.
Journal of Applied Physics 05/2008; 103(9):094101-094101-4. · 2.17 Impact Factor
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ABSTRACT: The specific heat of La <sub>0.4</sub> Ca <sub>0.6</sub> Mn O <sub>3</sub> in bulk and nanoparticle ( ∼60 nm in grain size) forms was investigated. It is found that the charge-ordered state highly stabilized in the bulk samples can be significantly suppressed in the nanoparticle. The low temperature specific heat data reveal a Schottky-like anomaly at ∼5 K for the bulk sample, while a large electronic linear term (γ=17.8 mJ / mole K <sup>2</sup>) was identified for the nanoparticle samples. The magnetic measurements unveil the small magnetic entropy as low as ∼0.255 J / kg K and the possible existence of a Griffiths-like phase in the nanoparticle samples. We argue that the physics underlying the size effect is associated with the dimension-dependent interactions based on which the ferromagnetic/charge-ordering transition occurs.
Journal of Applied Physics 05/2008; · 2.17 Impact Factor
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ABSTRACT: A magnetoelectric laminate composite with electric-field-induced magnetization (EIM) effect was prepared. It was found that the phase shift of EIM in the laminate was highly sensitive to the dc magnetic field near resonance frequency. The dependence of the phase shift of EIM on the dc magnetic field was theoretically and experimentally investigated. This work demonstrates that the phase shift of EIM in the magnetoelectric composite has potential for application of small dc magnetic field detection.
Journal of Physics D Applied Physics 01/2008; 41(3):035003. · 2.54 Impact Factor
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ABSTRACT: Highly ordered crystalline and amorphous Si nanoarrays have been formed by using self-assembled monolayer of polystyrene nanospheres as a template followed by dry ion etching treatments. The template was removed by annealing at 8°C and pattern transfer process was revealed by atomic force microscopy. It was shown that the ordered Si nanotips with a height about 70–80 nm and an average lateral size around 150 nm can be obtained. Field emission with low threshold electric field (<10 V/μm) was demonstrated for both samples which can be attributed to the enhancement of local field due to the existence of surface nanostructures. Our results provide a simple and cheap way to make Si field emitters.
Surface Review and Letters (SRL). 01/2007; 14(04):543-546.
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ABSTRACT: We report the electric-field-induced magnetization (EIM) in the composite structures made by combining Pb ( Zr <sub>0.52</sub> Ti <sub>0.48</sub>) O <sub>3</sub> (PZT) and Tb <sub>0.30</sub> Dy <sub>0.7</sub> Fe <sub>2</sub> (Terfenol-D). The results showed that the EIM could be generated in the composite structures due to the efficient stress-mediated electromagnetic coupling interaction between the piezoelectric PZT and magnetostrictive Terfenol-D. This EIM effect depended significantly on the driving electric field frequency and was highly sensitive to the dc magnetic bias, which exhibited a promising potential in the low-level dc magnetic field detecting application.
Applied Physics Letters 06/2006; · 3.84 Impact Factor
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ABSTRACT: A numerical modeling of the magnetoelectric (ME) effect in the bilayer structures lead zirconate titanate (PZT)/lanthanum strontium manganite (LSMO), PZT/nickel ferrite (NFO) and PZT/cobalt ferrite (CFO) is investigated for both static and dynamic behaviors. Mainly, this work focuses on the ME coupling of the rectangular bilayer structures at the electromechanical resonance (EMR) and predicts a resonance frequency that is found to increase with the decrease of length and the rise of PZT volume fraction. The calculated ME voltage coefficients versus frequency profiles for these three samples show a strong resonance character and the values at the EMR are about 200 times the values far from the EMR state. The estimated resonance frequencies are both at about 120kHz for 15-mm-long NFO/PZT and CFO/PZT bilayers with PZT volume fraction v=0.25. Furthermore, the relevant experiments were carried out to verify the numerical results.
Applied Physics A 10/2005; 81(6):1197-1202. · 1.63 Impact Factor
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ABSTRACT: We report the bending resonant magnetoelectric effect observed in the bilayer of magnetostrictive Tb0.30Dy0.7Fe2 (Terfenol-D)∕epoxy and piezoelectric Pb(Zr0.52Ti0.48)O3 (PZT). It has been found that the bilayer has both giant magnetoelectric voltage coefficient and high coupling efficiency when it operates at the first bending resonance mode. The maximum bending resonant magnetoelectric voltage coefficient of 14.6 V/cm Oe at quite low frequency of 12.5 kHz was observed in the bilayer of small sizes of 17.4×4.0×1.44 mm3. This bending-resonance-type magnetoelectric effect shows promising application in transducers for magnetoelectric energy conversion.
Applied Physics Letters 05/2005; 86(20):202504-202504-3. · 3.84 Impact Factor
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ABSTRACT: Magnetoelectric (ME) CoFe2O4–Pb(Zr,Ti)O3 composite thin films have been prepared by a sol-gel process and spin-coating technique. X-ray diffraction and scanning electron microscopy reveal that there exists local aggregation or phase separation of the CoFe2O4 and Pb(Zr,Ti)O3 phases in the films. Vibrating sample magnetometer, ferroelectric test unit, and magnetoelectric measuring device were used to characterize the magnetic and ferroelectric properties, as well as the ME effect of the films. It is shown that the films exhibit both good magnetic and ferroelectric properties, as well as a ME effect. A high initial magnetoelectric voltage coefficient for the film is observed. The ME effect of the film strongly depends on the magnetic bias and magnetic field frequency.
Applied Physics Letters 03/2005; 86(12):122501-122501-3. · 3.84 Impact Factor
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ABSTRACT: The bandwidth of magnetoelectric (ME) resonance for a combined structure where several Terfenol-D/epoxy-Pb(Zr,Ti)O3 bilayers are connected in parallel and series was measured. A relationship between the bilayer length and resonance frequency was used to design the combined structure, in which the bilayered components of different lengths were connected in the parallel and series forms, respectively. The measured giant ME effect of the combined structure showed a much wider frequency response to external field than a single bilayered structure, and the ME effect far from the resonance ranges was enhanced significantly too. A qualitative analysis based on the equivalent circuit concept was presented to explain these effects.
Applied Physics Letters 01/2005; 86(3):032508-032508-3. · 3.84 Impact Factor
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ABSTRACT: This paper presents a magnetoelectric (ME) heterostructure of a magnetostrictive Terfenol-D/epoxy 0-3 composite (MSCP) plate combined with a piezoelectric PZT/epoxy 0-3 composite (PECP) plate along the longitudinal direction. By keeping the dimensions of the MSCP at 6.8 mm × 6.2 mm × 0.7 mm, heterostructures with various PECP lengths of 8-15 mm are prepared and characterized to reveal their frequency dependence of the ME effect. The results exhibit several resonance peaks in the heterostructures due to the magnetomechanical resonances (MMR) of the MSCP and the electromechanical resonances (EMR) of the PECP. The superposition of the MMR and EMR enhances significantly the ME output of the heterostructures. The highest ME voltage coefficient (α<sub>E</sub>) of 13.1 V/cm·Oe is observed at the resonance frequency of 106.8 kHz when the length ratio of the MSCP and PECP is set to 6.8/10.2, together with an optimal magnetic bias field of 0.7 kOe.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: Magnetoelectric (ME) Pb(Zr0.52Ti0.48)O3 (PZT)–NiFe2O4 bulk composites with various PZT volume fractions were prepared. The ME coupling coefficient, impedance, and flux density versus the frequency were measured. The magnetic bias and PZT volume fraction in the composites are investigated to optimize the ME output. It is revealed that ME resonances are caused by electromechanical resonance in the piezoelectric phase and magnetomechanical resonance in the magnetostrictive phase. Maximum magnetoelectric voltage coefficient resonance values of 6.7 V/cm Oe at 132.6 kHz and 6.12 V/cm Oe at 427.2 kHz for the composite with optimized PZT volume fraction of 0.55 were obtained at optimized magnetic bias of 0.6 kOe. © 2004 American Institute of Physics.
Journal of Applied Physics 06/2004; 95(12):8069-8073. · 2.17 Impact Factor
