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21 Feb 2013

Volume 113, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 073506 (2013); http://dx.doi.org/10.1063/1.4790173 (6 pages)

Uwe Kaiser, Sebastian Gies, Sebastian Geburt, Franziska Riedel, Carsten Ronning, and Wolfram Heimbrodt
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back to top Electronic Structure and Transport

Understanding and resolving the discrepancy between differential and actual minority carrier lifetime

J. A. Giesecke, S. W. Glunz, and W. Warta

J. Appl. Phys. 113, 073706 (2013); http://dx.doi.org/10.1063/1.4790716 (8 pages) | Cited 1 time

Online Publication Date: 19 February 2013

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Differential light-biased dynamic measurements of charge carrier recombination properties in semiconductors have long been known to yield only differential rather than actual recombination properties. Therefore, the determination of injection-dependent recombination properties from such measurements was previously found to require integration over the entire injection range. Recent investigations of the phase shift between a time-modulated irradiation of silicon samples and excess carrier density reveal a striking analogy to the above findings: the phase shift is greater than the actual effective carrier lifetime in the case of a positive derivative of lifetime with respect to excess carrier density, and vice versa. This work attempts to rearrange the mentioned previous findings in a quantitative theoretical description of light-biased dynamic measurements of effective carrier lifetime. Both light-biased differential lifetime measurements as well as harmonically time-modulated methods without additional bias light are shown to represent a limiting case in a general treatment of light-biased dynamic lifetime measurements derived here. Finally, we sketch a way to obtain actual recombination properties from differential measurements—referred to as a differential-to-actual (d2a) lifetime analysis, which does not require integration over the entire injection range.
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81.05.Cy Elemental semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Achieving direct band gap in germanium through integration of Sn alloying and external strain

Suyog Gupta, Blanka Magyari-Köpe, Yoshio Nishi, and Krishna C. Saraswat

J. Appl. Phys. 113, 073707 (2013); http://dx.doi.org/10.1063/1.4792649 (7 pages)

Online Publication Date: 19 February 2013

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GeSn is predicted to exhibit an indirect to direct band gap transition at alloy Sn composition of 6.5% and biaxial strain effects are investigated in order to further optimize GeSn band structure for optoelectronics and high speed electronic devices. A theoretical model has been developed based on the nonlocal empirical pseudopotential method to determine the electronic band structure of germanium tin (GeSn) alloys. Modifications to the virtual crystal potential accounting for disorder induced potential fluctuations are incorporated to reproduce the large direct band gap bowing observed in GeSn alloys.
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71.20.Gj Other metals and alloys
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Lattice strain analysis of silicon fin field-effect transistor structures wrapped by Ge2Sb2Te5 liner stressor

Yinjie Ding, Ran Cheng, Anyan Du, and Yee-Chia Yeo

J. Appl. Phys. 113, 073708 (2013); http://dx.doi.org/10.1063/1.4792477 (8 pages)

Online Publication Date: 20 February 2013

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The local strain components in the source/drain (S/D) and channel regions of Si fin field-effect transistor (FinFET) structures wrapped around by a Ge2Sb2Te5 liner stressor were investigated for the first time using nano-beam diffraction. When the Ge2Sb2Te5 (GST) layer changes phase from amorphous to crystalline, it contracts and exerts a large stress on the Si fins. This results in large compressive strain in the S/D region of ⟨math10⟩-oriented Si FinFETs of up to −1.15% and −1.57% in the ⟨110⟩ (horizontal) and ⟨001⟩ (vertical) directions, respectively. In the channel region of the FinFETs under the metal gate, the GST contraction results in up to −1.47% and −0.61% compressive strain in the ⟨110⟩ and ⟨001⟩ directions, respectively. In the channel region, the ⟨110⟩ compressive strain is higher at the fin sidewalls and lower near the fin center, while the ⟨001⟩ compressive strain is lower at the sidewalls and higher near the center.
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85.30.Tv Field effect devices

Thermoelectric properties of p-type (Bi2Te3)x(Sb2Te3)1−x single crystals doped with 3 wt. % Te

Ö. Ceyda Yelgel and G. P. Srivastava

J. Appl. Phys. 113, 073709 (2013); http://dx.doi.org/10.1063/1.4792653 (8 pages)

Online Publication Date: 20 February 2013

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In the present work, thermoelectric properties of p-type (Bi2Te3)x (Sb2Te3)1−x single crystals doped with 3 wt. % Te are theoretically explored for various chemical compositions (x = 0.18, 0.19, 0.20, 0.22, 0.24, 0.26) in the temperature range of 290–500 K. The influence of the chemical composition in enhancing the thermoelectric figure of merit (ZT) is discussed in detail. Using the nearly-free electron approximation and the Fermi-Dirac statistics, the temperature dependences of Fermi level (Ef), Seebeck coefficient (S), and electrical conductivity (σ) are successfully reproduced as reported in the experimental study of Li et al. [Intermetallics 19, 2002 (2011)]. The thermal conductivity contributions from phonons (κph), acceptor holes (κh), and electron-hole pairs (κbp) are included by employing Srivastava's scheme, Wiedemann-Franz law, and Price's theory, respectively. By combining all three contributions of the thermal conductivity we successfully explain the experimental measurements of the total thermal conductivity as reported by Li et al. Furthermore, it is theoretically found that among all the compositions the p-type 20%(Bi2Te3)-80%(Sb2Te3) sample has the maximum ZT value of 1.31 at 390 K, which is also in good agreement with the experimental results obtained by Li et al.
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81.05.Hd Other semiconductors
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
71.20.Ps Other inorganic compounds
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Sk Insulators
72.80.Jc Other crystalline inorganic semiconductors

Directional quantum transport in graphyne p-n junction

Bumned Soodchomshom, I.-Ming Tang, and Rassmidara Hoonsawat

J. Appl. Phys. 113, 073710 (2013); http://dx.doi.org/10.1063/1.4792500 (8 pages)

Online Publication Date: 21 February 2013

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Graphyne, a newly proposed allotrope of carbon, has a structure which is topologically equivalent to that of a strongly distorted graphene [B. G. Kim and H. J. Choi, Phys. Rev. B 86, 115435 (2012)]. The energy gap between the valence and conduction bands is due to the symmetry breaking caused by there being three topologically inequivalent hoping elements. The valleyless fermionic transport properties of γ-graphyne are different from those of graphene since the two valleys are merged together in this carbon allotrope. The transmission and conductance of the electrons in γ-graphyne are found to be directionally dependent. Klein tunneling is predicted if the tunneling is in the y-direction. If the tunneling is in the x-direction, perfect back reflection (anti Klein tunneling) is predicted if the tunneling is at normal incidence. The consequences of these directional transport properties on the performances of p-n junctions fabricated with this carbon allotrope are studied. This work reveals the advantages of building p-n junctions based on γ-gaphyne.
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72.80.Vp Electronic transport in graphene
73.22.Pr Electronic structure of graphene
72.20.Ee Mobility edges; hopping transport
73.40.Gk Tunneling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
back to top Magnetism and Superconductivity

Thermal properties, magneto- and baro-caloric effects in La0.7Pb0.3MnO3 single crystal

A. V. Kartashev, E. A. Mikhaleva, M. V. Gorev, E. V. Bogdanov, A. V. Cherepakhin, K. A. Sablina, N. V. Mikhashonok, I. N. Flerov, and N. V. Volkov

J. Appl. Phys. 113, 073901 (2013); http://dx.doi.org/10.1063/1.4792044 (6 pages)

Online Publication Date: 15 February 2013

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The results of heat capacity, thermal dilatation and T-p phase diagram studies on the La0.7Pb0.3MnO3 single crystal are reported. Direct measurements of intensive magnetocaloric effect are performed by means of adiabatic calorimeter. Barocaloric effect is determined using data of heat capacity and susceptibility to hydrostatic pressure. Caloric efficiency of manganite in the vicinity of ferromagnetic phase transition is discussed and compared with that of other magnetic materials.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
81.30.Dz Phase diagrams of other materials
65.40.Ba Heat capacity
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Investigation of magnetic properties and microwave characteristics of obliquely sputtered NiFe/MnIr bilayers

Nguyen N. Phuoc, Wee Tee Soh, Guozhi Chai, and C. K. Ong

J. Appl. Phys. 113, 073902 (2013); http://dx.doi.org/10.1063/1.4792496 (6 pages)

Online Publication Date: 15 February 2013

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A comprehensive investigation of the magnetic properties and high frequency characteristics of NiFe/MnIr bilayers with regards to oblique deposition angle was conducted in conjunction with an analysis based on the Landau-Lifshitz-Gilbert equation. It was found that exchange bias can be significantly enhanced with the variation of oblique deposition angle, which is interpreted in terms of the formation of inclined columnar structure of the films often observed in samples fabricated by this oblique deposition technique. Moreover, the uniaxial magnetic anisotropy field and the resonance frequency are increased with the increasing of oblique deposition angle. The variations of effective Gilbert damping factor and the frequency linewidth with oblique deposition angle are also presented and discussed in details.
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81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Revisiting magnetic stripe domains — anisotropy gradient and stripe asymmetry

Jeffrey McCord, Burak Erkartal, Thomas von Hofe, Lorenz Kienle, Eckhard Quandt, Olga Roshchupkina, and Jörg Grenzer

J. Appl. Phys. 113, 073903 (2013); http://dx.doi.org/10.1063/1.4792517 (5 pages)

Online Publication Date: 15 February 2013

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The thickness dependent generation of magnetic stripe domains in NiFe films is investigated by in-depth magnetic domain and micromagnetic analysis, as well as complementary analysis of the microstructure by x-ray diffraction and transmission electron microscopy. A gradient of perpendicular magnetic anisotropy with film thickness is found. Micromagnetic simulations show that the anisotropy gradient results in an asymmetric stripe domain configuration. Columnar grain coarsening and texture development with thickness are derived from the microstructural investigations. The variations correspondingly lead to the gradient of magnetic anisotropy and to an asymmetric magnetic stripe domain structure.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.55.jm Texture
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure

Dependence of the switching current density on the junction sizes in spin transfer torque

Chun-Yeol You and Myung-Hwa Jung

J. Appl. Phys. 113, 073904 (2013); http://dx.doi.org/10.1063/1.4792728 (5 pages)

Online Publication Date: 19 February 2013

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We investigate the dependence of switching current density on the junction sizes in the in-plane spin transfer torque nanopillar structures by using micromagnetic simulations. While the macrospin model predicts weak dependence of switching current density on the junction sizes, we find that the switching current density is a sensitive function of the junction sizes. It can be explained with the complicated spin configurations and dynamics during the switching process. The detail spin configurations and dynamics are determined by spin wave excitation with the finite wave vector, which is related with the exchange coupling energy and junction shape.
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75.78.Cd Micromagnetic simulations
75.60.-d Domain effects, magnetization curves, and hysteresis
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Effect of barium-deficiency on the structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2−x◻xMnO3 (0 ≤ x ≤ 0.15)

R. M'nassri, W. Cheikhrouhou-Koubaa, N. Chniba Boudjada, and A. Cheikhrouhou

J. Appl. Phys. 113, 073905 (2013); http://dx.doi.org/10.1063/1.4792730 (7 pages)

Online Publication Date: 19 February 2013

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Structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2-x◻xMnO3 (0 ≤ x ≤ 0.15) where ◻ is a barium deficiency have been investigated by X-ray diffraction and magnetic measurements. Our samples were synthesized using the solid-state reaction method at high temperatures. Structural studies show that our samples are single phase and crystallize in the rhombohedral system with R math c space group. Magnetization measurements as a function of temperature in a magnetic applied field of 0.05 T show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature TC shifts to lower values with increasing barium-deficiency. The Arrott plots show that the phase transition is of second order. The effect of barium deficiency on the magnetocaloric properties has been investigated. The values of the maximum of the magnetic entropy change, |−ΔSmax|, under a magnetic field change of 3.5 T are found to be 2.9, 2.92, 3.31, and 3.34 J/kg K for x = 0.0, 0.05, 0.1, and 0.15, respectively.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.gd Entropy

Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing

P. J. Metaxas, P.-J. Zermatten, R. L. Novak, S. Rohart, J.-P. Jamet, R. Weil, J. Ferré, A. Mougin, R. L. Stamps, G. Gaudin, V. Baltz, and B. Rodmacq

J. Appl. Phys. 113, 073906 (2013); http://dx.doi.org/10.1063/1.4792216 (10 pages)

Online Publication Date: 19 February 2013

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Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially periodic domain wall pinning potentials. The potentials are generated non-destructively using the stray magnetic field of ordered arrays of magnetically hard [Co/Pt]m nanoplatelets, which are patterned above and are physically separated from the continuous magnetic layer. The effect of the periodic pinning potentials on thermally activated domain wall creep dynamics is shown to be equivalent, at first approximation, to that of a uniform, effective retardation field, Hret, which acts against the applied field, H. We show that Hret depends not only on the array geometry but also on the relative orientation of H and the magnetization of the nanoplatelets. A result of the latter dependence is that wall-mediated hysteresis loops obtained for a set nanoplatelet magnetization exhibit many properties that are normally associated with ferromagnet/antiferromagnet exchange bias systems. These include a switchable bias, coercivity enhancement, and domain wall roughness that is dependent on the applied field polarity.
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81.05.Bx Metals, semimetals, and alloys
81.07.-b Nanoscale materials and structures: fabrication and characterization
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetocaloric effect in inhomogeneous ferromagnets

N. G. Bebenin, R. I. Zainullina, and V. V. Ustinov

J. Appl. Phys. 113, 073907 (2013); http://dx.doi.org/10.1063/1.4792306 (7 pages)

Online Publication Date: 19 February 2013

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The article is devoted to the theoretical study of magnetocaloric effect in imhomogeneous ferromagnets in vicinity of magnetic phase transitions of first and second orders as well as in vicinity of tricritical and critical points. In the frame of Landau theory the formulae for the magnetic field induced entropy change are derived. The theory is compared with the experimental data obtained on single crystals of La0.7Ba0.3MnO3 (second order transition) and La0.7Ca0.3MnO3 (first order transition).
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.-s Critical-point effects, specific heats, short-range order
75.50.Dd Nonmetallic ferromagnetic materials
71.70.Di Landau levels
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

The competing spin orders and fractional magnetization plateaus of the classical Heisenberg model on Shastry-Sutherland lattice: Consequence of long-range interactions

L. Huo, W. C. Huang, Z. B. Yan, X. T. Jia, X. S. Gao, M. H. Qin, and J.-M. Liu

J. Appl. Phys. 113, 073908 (2013); http://dx.doi.org/10.1063/1.4792504 (6 pages) | Cited 1 time

Online Publication Date: 20 February 2013

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The competing spin orders and fractional magnetization plateaus of the classical Heisenberg model with long-range interactions on a Shastry-Sutherland lattice are investigated using Monte Carlo simulations, in order to understand the fascinating spin ordering sequence observed in TmB4 and other rare-earth tetraborides. The simulation reproduces the experimental 1/2 magnetization plateau at low temperature by considering multifold long range interactions. It is found that more local long range interactions can be satisfied in the 1/2 plateau state than those in the 1/3 plateau state, leading to the stabilization of the extended 1/2 plateau. The phase boundaries in the magnetic field at zero temperature are determined, demonstrating the simulation results. When the energies of the Neel state and the collinear state are degenerated, the former state is more likely to be stabilized due to the competitions among the local collinear spin orders. The present work provides a comprehensive proof of the phase transitions to the Neel state at nonzero temperature, in complimentary to the earlier predictions for the Fe-based superconductors.
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75.10.Hk Classical spin models
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Mg Numerical simulation studies
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Control of magnetic loss tangent of hexaferrite for advanced radio frequency antenna applications

Jaejin Lee, Yang-Ki Hong, Woncheol Lee, Gavin S. Abo, Jihoon Park, Won-Mo Seong, and Won-Ki Ahn

J. Appl. Phys. 113, 073909 (2013); http://dx.doi.org/10.1063/1.4793089 (6 pages)

Online Publication Date: 21 February 2013

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We demonstrate that magnetic loss tangent of M-type hexaferrite can be controlled by a small dc magnetic field, thereby improving radio frequency (RF) antenna radiation efficiency and realizing antenna miniaturization. Magnetic loss tangent (tan δμ) of the M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite at 200 MHz decreased significantly from 11.8% to less than 1% as the applied dc magnetic field increased from 0 to 400 Oe. This is because the contribution of domain wall motion to permeability dispersion is decreased, and the ferromagnetic resonance frequency increases with the magnetic field. Antenna simulation results showed that radiation efficiency of the designed ferrite helical antenna increased from −22.9 to −9.2 dB with dc magnetic field of 400 Oe. Therefore, the small dc magnetic field played a key role in reduction of tan δμ of hexaferrite and improvement of antenna performance in the RF range.
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84.40.Ba Antennas: theory, components and accessories
75.50.Gg Ferrimagnetics
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Ge1−xMnx heteroepitaxial quantum dots: Growth, morphology, and magnetism

J. Kassim, C. Nolph, M. Jamet, P. Reinke, and J. Floro

J. Appl. Phys. 113, 073910 (2013); http://dx.doi.org/10.1063/1.4792221 (7 pages)

Online Publication Date: 21 February 2013

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Heteroepitaxial Ge1-xMnx quantum dots (QDs) were grown on Si (001) by molecular beam epitaxial co-deposition, with x = 0 to 0.10, in order to explore the interaction between Mn content, surface morphological evolution, and magnetism. Morphological evolution typical of the Ge/Si (001) system was observed, where the effect of Mn on surface morphology is surprisingly minimal at low Mn content, with no obvious surface morphological indicators of second phase formation. As the Mn content increases, secondary phase formation becomes evident, appearing to heterogeneously nucleate on or within Ge QDs. Still higher Mn concentrations lead to extensive second phase formation interspersed with an array of Ge QDs. Although ferromagnetism up to 220 K is observed, likely arising from intermetallic precipitates, there is no clear evidence for room-temperature ferromagnetism associated with a dilute magnetic solution phase.
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81.05.Cy Elemental semiconductors
75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.07.Ta Quantum dots

A simple formulation for magnetoresistance in metal-insulator granular films with increased current

M. A. S. Boff, B. Canto, M. N. Baibich, and L. G. Pereira

J. Appl. Phys. 113, 073911 (2013); http://dx.doi.org/10.1063/1.4793272 (4 pages)

Online Publication Date: 21 February 2013

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We studied the tunnel magnetoresistance in metal/insulator granular films when the applied current is varied. The tunnel magnetoresistance shows a strong modification related to a non-Ohmic behaviour of theses materials. It was verified that spin-dependent tunnelling is the main mechanism for magnetoresistance at low applied current. However, when the current is high, another mechanism gets to be important: it is independent of the magnetization and is associated to variable range hopping between metallic grains. In this work, we propose a simple modification of Inoue and Maekawa's model for tunnelling magnetoresistance in granulars, rewriting the expression for resistance as a function of magnetic field and temperature, also taking into account the two different contributions.
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81.05.Rm Porous materials; granular materials
72.25.-b Spin polarized transport
73.50.Dn Low-field transport and mobility; piezoresistance
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Reducing the writing field of L10-FePt by graded order parameter

Zhihong Lu, Junbo Guo, Zhanghua Gan, Yong Liu, Rui Xiong, G. J. Mankey, and W. H. Butler

J. Appl. Phys. 113, 073912 (2013); http://dx.doi.org/10.1063/1.4791583 (5 pages)

Online Publication Date: 21 February 2013

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The dependence of the magnetic properties of epitaxial Fe50Pt50 films on order parameter (S) was investigated. It was demonstrated that the magnetic anisotropy could be tuned by controlling S which can be controlled by the growth temperature. Based on this result, two kinds of multilayered structures, each with a 13 nm fully ordered Fe50Pt50 layer as the bottom layer, were built: (1) 4-layered structure with S decreasing layer by layer from bottom to top; (2) graded structure with S changing more continuously along the thickness. The magnetic properties of the films were characterized using vibrating sample magnetometry. It was found that both structures have their easy axis perpendicular to the film; the anisotropy fields of the 4-layered film and the graded film are 53 kOe and 37 kOe, respectively. These values are much lower than that of the fully ordered uniform Fe50Pt50 film (about 73 kOe). The results suggest that it may be possible to reduce the writing field of Fe50Pt50 by gradually changing the order parameter.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

A flow simulation study of protein solution under magnetic forces

Hidehiko Okada, Noriyuki Hirota, Shinji Matsumoto, and Hitoshi Wada

J. Appl. Phys. 113, 073913 (2013); http://dx.doi.org/10.1063/1.4792650 (8 pages)

Online Publication Date: 21 February 2013

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We have developed a superconducting magnet system generating magnetic forces able to compensate gravity and suppress convection of diamagnetic protein solution from which protein crystals precipitate. A simulation model has been proposed to elucidate the motion of protein solutions and search for the optimal conditions of the crystal formation process. This model incorporates general, non-uniform magnetic forces as external forces, while the previous models involve only simple, uniform magnetic forces. The simulation results indicate that the vertical component can suppress the convection of protein solution, while the horizontal component induces minimal convection. We, therefore, need to take into account the both components when considering the formation of protein crystals under magnetic forces.
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87.14.E- Proteins
back to top Dielectrics and Ferroelectricity

Evolution of polar order in (1 − x)Pb(In1/2Nb1/2)O3-xPbTiO3 (0 ≤ x ≤ 1) system as investigated by dielectric and Raman spectroscopy

G. Ramesh, V. Subramanian, and V. Sivasubramanian

J. Appl. Phys. 113, 074101 (2013); http://dx.doi.org/10.1063/1.4791572 (7 pages)

Online Publication Date: 15 February 2013

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We have investigated the (1 − x)Pb(In1/2Nb1/2)O3 − xPbTiO3 (PIN-PT) solid solution by Raman scattering and temperature variation of dielectric measurement. The dielectric analysis indicates that the Burn's temperature (TB) raises upto x = 0.30 and then decreases due to the enhancement in the long range ferroelectric order. At x = 0.60, TB coincides with the temperature at which dielectric constant is maximum, Tm, (TB ∼ Tm). It suggests that the polar nanoregions (PNRs) are not present in 0.40PIN-0.60PT. The investigation confirms that PT addition in PIN transforms the PNRs into the macroscopic ferroelectric domains. The composition dependent Raman spectra are used to interpret the evolution of polar order. Qualitative Raman analysis reveals that the changes in the vibration bands are associated with the structural transition from R3m to P4mm at morphotrophic phase region. For the values of x > 0.41, the line-width of all the bands decreases as the concentration of PT increases. The observed two mode behavior in the highest frequency region (800 cm−1) hints the existence of chemical inhomogenetiy at nanometer scale such as the local segregation of Ti and In/Nb-rich regions.
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77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
78.30.Hv Other nonmetallic inorganics
64.75.Nx Phase separation and segregation in solid solutions
77.80.B- Phase transitions and Curie point
77.80.Jk Relaxor ferroelectrics

The electrostatics of Ta2O5 in Si-based metal oxide semiconductor devices

Lior Kornblum, Boris Meyler, Joseph Salzman, and Moshe Eizenberg

J. Appl. Phys. 113, 074102 (2013); http://dx.doi.org/10.1063/1.4792750 (5 pages)

Online Publication Date: 20 February 2013

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Thin dielectric layers are a prominent route to control the band alignments and effective work function of metal oxide semiconductor (MOS) devices. In this work, the electrostatic effects of thin Ta2O5 layers on the band alignments of MOS devices are examined. A detailed analysis of the physical properties of a thick (∼6 nm) Ta2O5 layer is reported. No significant dipoles at Ta2O5-Al2O3 and Ta2O5-SiO2 interfaces are found, as well as any significant charges inside Ta2O5 layers. When positioned at the interface, Ta2O5 is shown to prevent the formation of band offsets between Al2O3-SiO2, resulting in a shift of 1 ± 0.2 eV versus samples without interfacial Ta2O5. The relatively large magnitude of this shift in the current experimental configuration compared to previous works may indicate the participation of interface charges in the band offset. The possible use for these effects in devices is discussed.
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68.60.-p Physical properties of thin films, nonelectronic
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Ct Interface structure and roughness
85.30.Tv Field effect devices

Ferroelectric and dielectric properties of ferrite-ferroelectric ceramic composites

Cristina Elena Ciomaga, Alexandra Maria Neagu, Mihai Valentin Pop, Mirela Airimioaei, Sorin Tascu, Giorgio Schileo, Carmen Galassi, and Liliana Mitoseriu

J. Appl. Phys. 113, 074103 (2013); http://dx.doi.org/10.1063/1.4792494 (7 pages)

Online Publication Date: 20 February 2013

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Particulate composites of ferrite and ferroelectric phases with xNiFe2O4 (NF) and (1 − x)Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 (where x = 2, 10, 20, 30, 50, 70, and 100 wt. %) were prepared in situ by sol-gel method. The presence of a diphase composition was confirmed by X-ray diffraction while the microstructure of the composites was studied by scanning electron microscopy revealing a good mixing of the two phases and a good densification of the bulk ceramics. The dielectric permittivity shows usual dielectric dispersion behavior with increasing frequency due to Maxwell-Wagner interfacial polarization. AC conductivity measurements made in frequency range 1 Hz-1 MHz suggest that the conduction process is due to mixed polaron hopping. The effect of NF phase concentration on the P-E and M-H hysteresis behavior and dielectric properties of the composites was investigated. At low NF concentration a sharp ferro-paraelectric transition peak can be observed at around 360 °C while for higher NF concentrations a trend to a diffuse phase transition occurs. All the composite samples exhibit typical ferromagnetic hysteresis loops, indicating the presence of ordered magnetic structure.
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77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.B- Phase transitions and Curie point
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Electrical measurements of dielectric nonlinearities in ferroelectric bilayer thin films

Pavel Salev, Mandana Meisami-Azad, and Alexei Grigoriev

J. Appl. Phys. 113, 074104 (2013); http://dx.doi.org/10.1063/1.4792601 (6 pages)

Online Publication Date: 20 February 2013

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Frequency dependence of the dielectric response is studied for ferroelectric bilayer thin-film capacitors under a cyclic bias voltage. The approach used in this work enables probing strong dielectric nonlinearities at millisecond and microsecond time scales during polarization switching in thin films. The frequency-dependent changes that are observed in the relative dielectric permittivity of PbZr0.8Ti0.2O3/PbZr0.6Ti0.4O3 and PbZr0.6Ti0.4O3/PbZr0.2Ti0.8O3 epitaxial bilayers without applying the cyclic bias are small in the kHz-to-MHz frequency range. When the bias is applied, a strong frequency dependence of the relative dielectric permittivity is observed during polarization switching. For instance, the permittivity of the PbZr0.6Ti0.4O3/PbZr0.2Ti0.8O3 bilayer changes from εr ≈ 300 at 100 kHz to εr ≈ 1600 at 2 kHz. The observed frequency dependence of the permittivity can be described by [1+mathln(math)]2 that has been proposed for dynamic response in systems involving pinning at two-dimensional domain walls.
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84.32.Tt Capacitors

Room-temperature single phase multiferroic magnetoelectrics: Pb(Fe, M)x(Zr,Ti)(1−x)O3 [M = Ta, Nb]

Dilsom A. Sanchez, Nora Ortega, Ashok Kumar, G. Sreenivasulu, Ram S. Katiyar, J. F. Scott, Donald M. Evans, Miryam Arredondo-Arechavala, A. Schilling, and J. M. Gregg

J. Appl. Phys. 113, 074105 (2013); http://dx.doi.org/10.1063/1.4790317 (7 pages)

Online Publication Date: 20 February 2013

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We describe extensive studies on a family of perovskite oxides that are ferroelectric and ferromagnetic at ambient temperatures. The data include x-ray diffraction, Raman spectroscopy, measurements of ferroelectric and magnetic hysteresis, dielectric constants, Curie temperatures, electron microscopy (both scanning electron microscope and transmission electron microscopy (TEM)) studies, and both longitudinal and transverse magnetoelectric constants α33 and α31. The study extends earlier work to lower Fe, Ta, and Nb concentrations at the B-site (from 15%–20% down to 5%). The magnetoelectric constants increase supralinearly with Fe concentrations, supporting the earlier conclusions of a key role for Fe spin clustering. The room-temperature orthorhombic C2v point group symmetry inferred from earlier x-ray diffraction studies is confirmed via TEM, and the primitive unit cell size is found to be the basic perovskite Z = 1 structure of BaTiO3, also the sequence of phase transitions with increasing temperature from rhombohedral to orthorhombic to tetragonal to cubic mimics barium titanate.
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75.85.+t Magnetoelectric effects, multiferroics
61.66.Fn Inorganic compounds
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.80.Dj Domain structure; hysteresis

Complete set of elastic, dielectric, and piezoelectric constants of [011]C poled rhombohedral Pb(In0.5Nb0.5)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3:Mn single crystals

Xiaoqing Huo, Shujun Zhang, Gang Liu, Rui Zhang, Jun Luo, Raffi Sahul, Wenwu Cao, and Thomas R. Shrout

J. Appl. Phys. 113, 074106 (2013); http://dx.doi.org/10.1063/1.4792661 (5 pages)

Online Publication Date: 20 February 2013

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Mn modified rhombohedral Pb(In0.5Nb0.5)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT:Mn) single crystals poled along [011]C crystallographic direction exhibit a “2R” engineered domain configuration, with macroscopic mm2 symmetry. The complete sets of material constants were determined using combined resonance and ultrasonic methods, and compared to [001]C poled PIN-PMN-PT:Mn crystals. The thickness shear piezoelectric coefficient d15 and electromechanical coupling factor k15 were found to be on the order of ∼3000 pC/N and 0.92, respectively, with longitudinal piezoelectric coefficient d33 and coupling factor k33 being on the order of ∼1050 pC/N and 0.90. Of particular importance is that PIN-PMN-PT:Mn single crystals exhibited high mechanical quality factor Q33 ∼ 1000, comparable to “hard” PZT8 ceramics, which can also be confirmed by the low extrinsic contribution, being ≤2% from the Rayleigh analysis.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.22.Ej Polarization and depolarization
61.66.Fn Inorganic compounds
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants

Epitaxial PbxZr1−xTiO3 on GaN

E. A. Paisley, H. S. Craft, M. D. Losego, H. Lu, A. Gruverman, R. Collazo, Z. Sitar, and J.-P. Maria

J. Appl. Phys. 113, 074107 (2013); http://dx.doi.org/10.1063/1.4792599 (6 pages)

Online Publication Date: 21 February 2013

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Epitaxial integration of PbxZr1−xTiO3 (PZT) (111) with GaN (0002) presents the possibility of polarity coupling across a functional-oxide/nitride heteropolar interface. This work describes the synthesis and characterization of such thin film heterostructures by magnetron sputtering, with specific attention given to process optimization. Using x-ray diffraction and electrical characterization, the growth of epitaxial PZT (∼250 nm) on GaN and PZT on MgO/GaN stacks was verified. A two-stage growth process was developed for epitaxial PZT with a deposition temperature of 300 °C and an ex-situ anneal at 650 °C, which was effective in mitigating interfacial reactions and promoting phase-pure perovskite growth. Electrical analysis of interdigital capacitors revealed a nonlinear and hysteretic dielectric response consistent with ferroelectric PZT. Piezoresponse force microscopy (PFM) characterization shows clear evidence of ferroelectric switching, and PFM hysteresis loop analysis shows minimal evidence for direct polarity coupling, but suggests that band offsets which accompany the oxide-nitride heterostructures influence switching.
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77.80.Fm Switching phenomena
77.84.Cg PZT ceramics and other titanates
77.55.Px Epitaxial and superlattice films
77.55.hj PZT
77.65.-j Piezoelectricity and electromechanical effects
77.80.Dj Domain structure; hysteresis
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