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14 Feb 2011

Volume 98, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 073101 (2011); http://dx.doi.org/10.1063/1.3554360 (3 pages)

Wei Xu, Rajesh Leeladhar, Yao-Tsan Tsai, Eui-Hyeok Yang, and Chang-Hwan Choi
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Structural and electronic interaction at CuO-hexa-peri-hexabenzocoronene hybrid interface

Bharti Singh, B. R. Mehta, M. Singh, Govind Gupta, L. Dössel, X. Feng, and K. Müllen

Appl. Phys. Lett. 98, 072101 (2011); http://dx.doi.org/10.1063/1.3544937 (3 pages) | Cited 2 times

Online Publication Date: 14 February 2011

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Interfacial interaction at hybrid interfaces results in structural and electronic properties different from organic and inorganic components. In this study, x-ray photoelectron spectroscopy analysis carried out on CuO-hexa-peri-hexabenzocoronene (HBC) bilayers shows the appearance of an additional C 1s peak at lower energy due to Cu–C interaction. Spectroscopic ellipsometry investigation shows that interfacial layer ( ∼ 4 nm) has absorption features related to Cu–C bonding, modified HBC valence states, and Cu2+-π electron interaction. The observed resistive switching property of the CuO-HBC layers is considerably different from junction properties of HBC and CuO layers and is directly related to the hybrid interfacial layer.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.63.Bd Nanocrystalline materials
78.67.Sc Nanoaggregates; nanocomposites
79.60.Jv Interfaces; heterostructures; nanostructures

Electron band alignment at the interface of (100)GaSb with molecular-beam deposited Al2O3

V. V. Afanas’ev, H.-Y. Chou, A. Stesmans, C. Merckling, and X. Sun

Appl. Phys. Lett. 98, 072102 (2011); http://dx.doi.org/10.1063/1.3549878 (3 pages) | Cited 3 times

Online Publication Date: 14 February 2011

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From internal photoemission and photoconductivity measurements at the (100)GaSb/Al2O3 interface, the semiconductor valence band is found to be 3.05±0.10 eV below the oxide conduction band. This band alignment corresponds to conduction and valence band offsets of 2.3±0.10 and 3.05±0.15 eV, respectively. These results indicate that the valence band in GaSb lies energetically well above the valence band in InxGa1−xAs (0 ≤ x ≤ 0.53) or InP, suggesting the possibility of fabrication of hole quantum-well channel structures.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Jv Interfaces; heterostructures; nanostructures
72.40.+w Photoconduction and photovoltaic effects

Effect of edge threading dislocations on the electronic structure of InN

E. Kalesaki, J. Kioseoglou, L. Lymperakis, Ph. Komninou, and Th. Karakostas

Appl. Phys. Lett. 98, 072103 (2011); http://dx.doi.org/10.1063/1.3553772 (3 pages) | Cited 6 times

Online Publication Date: 15 February 2011

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The open issue of the n-type conductivity and its correlation to threading dislocations (TDs) in InN is addressed through first principles calculations on the electronic properties of a-edge TDs. All possible dislocation core models are considered (4-, 5/7-, and 8-atom cores) and are found to modify the band structure of InN in a distinct manner. In particular, nitrogen and indium low coordinated atoms in the eight-atom core induce states near the valence band maximum and above the conduction band minimum, respectively. The formation of a nitrogen–nitrogen “wrong” bond is observed at the 5/7-atom core resulting in a state inside the band gap. The 4- and 5/7-atom cores induce occupied states resonant in the conduction band due to In–In strain induced interactions and wrong bonds, respectively. These occupied states designate TDs as a source of higher electron concentrations in InN and provide direct evidence that TDs contribute to its inherent n-type conductivity.
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71.55.Eq III-V semiconductors
61.72.Lk Linear defects: dislocations, disclinations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
71.20.Nr Semiconductor compounds

Role of nonradiative recombination centers and extended defects in nonpolar GaN on light emission efficiency

A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, H. Amano, S. J. Pearton, I.-H. Lee, Q. Sun, J. Han, and S. Yu. Karpov

Appl. Phys. Lett. 98, 072104 (2011); http://dx.doi.org/10.1063/1.3555470 (3 pages) | Cited 7 times

Online Publication Date: 15 February 2011

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The correlation of integrated microcathodoluminescence efficiency with crystalline quality and deep trap density of nonpolar GaN films grown by metal organic chemical vapor deposition on semi-insulating 6H-m-SiC or r-sapphire is analyzed. The results suggest a strong influence of nonradiative recombination centers whose concentration decreases with decreased density of extended defects. Electron traps with energy levels at Ec−0.6 eV and which pin the Fermi level in films with high defect density are the most likely candidates for the decrease in light emission efficiency in nonpolar GaN.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.jn Color centers
71.55.Eq III-V semiconductors
68.55.ag Semiconductors

Unchanged thermopower enhancement at the semiconductor-metal transition in correlated FeSb2−xTex

P. Sun, M. Søndergaard, Y. Sun, S. Johnsen, B. B. Iversen, and F. Steglich

Appl. Phys. Lett. 98, 072105 (2011); http://dx.doi.org/10.1063/1.3556645 (3 pages) | Cited 9 times

Online Publication Date: 16 February 2011

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Substitution of Sb in FeSb2 by less than 0.5% of Te induces a transition from a correlated semiconductor to an unconventional metal with large effective charge carrier mass m∗. Spanning the entire range of the semiconductor-metal crossover, we observed an almost constant enhancement of the measured thermopower compared to that estimated by the classical theory of electron diffusion. Using the latter for a quantitative description one has to employ an enhancement factor of 10–30. Our observations point to the importance of electron-electron correlations in the thermal transport of FeSb2, and suggest a route to design thermoelectric materials for cryogenic applications.
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81.05.Hd Other semiconductors
72.80.Jc Other crystalline inorganic semiconductors
72.60.+g Mixed conductivity and conductivity transitions
72.20.Pa Thermoelectric and thermomagnetic effects

Photoconductivity in inverse silicon opals enhanced by slow photon effect: Yet another step towards optically amplified silicon photonic crystal solar cells

Takashi Suezaki, Hiroshi Yano, Tomoaki Hatayama, Geoffrey A. Ozin, and Takashi Fuyuki

Appl. Phys. Lett. 98, 072106 (2011); http://dx.doi.org/10.1063/1.3555338 (3 pages) | Cited 3 times

Online Publication Date: 16 February 2011

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While silicon photonic crystals have promised revolutionary advances in the field of optical telecommunications and optical computing, it has only recently been realized that their prowess to trap and slow photons could potentially improve the efficiency of silicon solar cells. In this work, spectral responses for the electrical properties of inverse silicon opals are evaluated and show a correlation with photonic bandgaps. In particular, a sign of the enhanced photoelectric generation by the slow photon effect is observed at the edges of photonic bandgaps.
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72.40.+w Photoconduction and photovoltaic effects
78.56.-a Photoconduction and photovoltaic effects
72.80.Cw Elemental semiconductors
42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Roles of silver oxide in the bipolar resistance switching devices with silver electrode

C. Y. Dong, D. S. Shang, L. Shi, J. R. Sun, B. G. Shen, F. Zhuge, R. W. Li, and W. Chen

Appl. Phys. Lett. 98, 072107 (2011); http://dx.doi.org/10.1063/1.3556618 (3 pages) | Cited 5 times

Online Publication Date: 17 February 2011

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Three devices, Ag/WO3−x/Pt, Ag/AgOx/Pt, and Ag/AgOx/WO3−x/Pt, were investigated to elucidate the influence of the silver oxide on the bipolar resistive switching behavior. The silver oxide films were obtained by depositing silver at oxygen atmosphere. We find that the resistive switching behavior was determined by the silver oxide layer. Bulk and interface resistive switching were observed in the Ag/AgOx/Pt and Ag/AgOx/WO3−x/Pt devices, respectively. By the micro-x-ray photoemission spectroscopy analysis, it was demonstrated that the electrochemical redox reaction occurred in the AgOx layer is responsible for the resistive switching behavior at silver/oxide interface.
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73.40.Rw Metal-insulator-metal structures
73.50.-h Electronic transport phenomena in thin films
72.20.-i Conductivity phenomena in semiconductors and insulators
82.45.Fk Electrodes

Enhancement-mode AlGaN/GaN heterostructure field effect transistors fabricated by selective area growth technique

Yuhua Wen, Zhiyuan He, Jialin Li, Ruihong Luo, Peng Xiang, Qingyu Deng, Guangning Xu, Zhen Shen, Zhisheng Wu, Baijun Zhang, Hao Jiang, Gang Wang, and Yang Liu

Appl. Phys. Lett. 98, 072108 (2011); http://dx.doi.org/10.1063/1.3553229 (3 pages)

Online Publication Date: 17 February 2011

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In this letter, a method of using selective area growth (SAG) technique was proposed to fabricate the enhancement-mode (E-mode) AlGaN/GaN heterostructure field effect transistors (HFETs), which can effectively avoid the plasma treatment damage to the active region of HFETs in comparison with the conventional methods. The SAG-HFETs exhibited a good performance of the maximum drain current of 300 mA/mm and peak transconductance of 135 mS/mm with a larger positive threshold voltage of 0.4 V. The results indicate that the SAG technique is a promising method to realize the high performance E-mode GaN based HFETs.
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85.30.Tv Field effect devices

Great thermoelectric power factor enhancement of CoSb3 through the lightest metal element filling

Jianjun Zhang, Bo Xu, Li-Min Wang, Dongli Yu, Zhongyuan Liu, Julong He, and Yongjun Tian

Appl. Phys. Lett. 98, 072109 (2011); http://dx.doi.org/10.1063/1.3557068 (3 pages) | Cited 4 times

Online Publication Date: 17 February 2011

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Lithium, the lightest metal element with a small ionic radius, is successfully filled into the voids of CoSb3 by utilizing the high pressure synthesis technique. The synthesized Li0.4Co4Sb12 shows the largest thermoelectric power factor of 6000 μW m−1 K−2 among all elemental filled CoSb3 materials. This significantly enhanced thermoelectric power factor is attributed to the large carrier mobility of Li0.4Co4Sb12, 61 cm2 V−1 s−1, featuring a good electron crystal property for the Li-filled CoSb3 samples.
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81.05.Bx Metals, semimetals, and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
62.50.-p High-pressure effects in solids and liquids
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Numerical simulations of space charge waves in InP films and microwave frequency conversion under negative differential conductivity

Abel Garcia-Barrientos and Vassil Palankovski

Appl. Phys. Lett. 98, 072110 (2011); http://dx.doi.org/10.1063/1.3555467 (3 pages)

Online Publication Date: 17 February 2011

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Numerical simulations of amplification and propagation of space charge waves in InP films is investigated theoretically. A microwave frequency conversion using the negative differential conductivity phenomenon is carried out when the harmonics of the input signal are generated. An increment in the amplification is observed in n-InP films at essentially higher frequencies f<70 GHz, when compared with n-GaAs films f<44 GHz. This work provides a way to achieve a frequency conversion and amplification of micrometer and millimeter waves.
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73.61.Ey III-V semiconductors
78.70.Gq Microwave and radio-frequency interactions

Multifunctional Ti1−xTaxO2: Ta doping or alloying?

A. Roy Barman, M. Motapothula, A. Annadi, K. Gopinadhan, Y. L. Zhao, Z. Yong, I. Santoso, Ariando, M. Breese, A. Rusydi, S. Dhar, and T. Venkatesan

Appl. Phys. Lett. 98, 072111 (2011); http://dx.doi.org/10.1063/1.3553773 (3 pages) | Cited 5 times

Online Publication Date: 18 February 2011

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Useful electronic, magnetic, and optical properties have been proposed and observed in thin films of Ti1−xMxO2 (M = Ta,Nb,V). In this work, we have studied phase formation for films of Ti1−xTaxO2 prepared by pulsed laser deposition. We show that substitutional Ta in TiO2 results in a different material system in terms of its electronic properties. Moss–Burstein shift is ruled out by comparing the electrical transport data of anatase and rutile TiO2. Vegard’s law fit to the blueshift data and the high energy optical reflectivity studies confirm the formation of an alloy with a distinct band structure.
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81.15.Fg Pulsed laser ablation deposition
78.40.Fy Semiconductors
81.30.Dz Phase diagrams of other materials
78.66.Li Other semiconductors
61.72.up Other materials
71.20.Nr Semiconductor compounds
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Asymmetric double-shifted characteristics in epitaxial (002) exchange-biased IrMn/CoFe bilayers

Hsin-Hung Huang, Chih-Yen Yang, Hsiu-Hau Lin, and Chih-Huang Lai

Appl. Phys. Lett. 98, 072501 (2011); http://dx.doi.org/10.1063/1.3554384 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2011

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Symmetric and asymmetric double-shifted loops were observed at room temperature in epitaxial (002) Ir20Mn80/Co50Fe50 samples placed in a setting field applied along collinear and noncollinear directions with the deposition-field direction, respectively. A coherent rotation model with extra unidirectional exchange and uniaxial anisotropies induced by the noncollinear setting field is proposed to explain the asymmetric double-shifted loops. Due to the existence of the biaxial magnetocrystalline anisotropy, the noncollinear setting field results in two interfacial Ir20Mn80 spin orientations, where the major spins determine the direction to observe double-shifted loops and the minor spins determine the field-shift and the asymmetry of double-shifted loops.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves

Exchange-spring behavior in nanopowders of CoFe2O4–CoFe2

J. M. Soares, F. A. O. Cabral, J. H. de Araújo, and F. L. A. Machado

Appl. Phys. Lett. 98, 072502 (2011); http://dx.doi.org/10.1063/1.3552677 (3 pages) | Cited 5 times

Online Publication Date: 15 February 2011

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The nature of the magnetic interactions among core-shell nanoparticles of CoFe2O4–CoFe2 having an average particle size of 32 nm were investigated by δm plots. It was found that the interactions are mainly demagnetizing in nature for nanoparticles with core diameters larger than 26 nm. For smaller values of core diameters, the exchange-spring phenomenon takes place due to the exchange-coupling at the core-shell interface. The critical thickness of the shell was estimated to be 7.8 nm. The overall results are in excellent agreement with current theoretical models.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Et Exchange and superexchange interactions
75.60.-d Domain effects, magnetization curves, and hysteresis

Josephson tunnel junctions in a magnetic field gradient

R. Monaco, J. Mygind, and V. P. Koshelets

Appl. Phys. Lett. 98, 072503 (2011); http://dx.doi.org/10.1063/1.3555464 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2011

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We measured the magnetic field dependence of the critical current of high-quality Nb-based planar Josephson tunnel junctions in the presence of a controllable nonuniform field distribution. We found skewed and slowly changing magnetic diffraction patterns quite dissimilar from the Fraunhofer-like ones typical of a homogeneous field. Our findings can be well interpreted in terms of recent theoretical predictions [R. Monaco, J. Appl. Phys. 108, 033906 (2010)] for a uniform magnetic field gradient, leading to Fresnel-like magnetic diffraction patterns. We also show that Fiske resonances can be suppressed by an asymmetric magnetic field profile.
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74.50.+r Tunneling phenomena; Josephson effects

Flux requirements for the growth of RFeAsO (R = rare earth) superconductors

J.-Q. Yan, B. Jensen, K. W. Dennis, R. W. McCallum, and T. A. Lograsso

Appl. Phys. Lett. 98, 072504 (2011); http://dx.doi.org/10.1063/1.3555632 (3 pages)

Online Publication Date: 16 February 2011

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Millimeter-sized LaFeAsO single crystals have been successfully grown out of NaAs flux starting with (LaAs+1/2Fe2O3):20NaAs. The factors which allow the growth of these crystals out of NaAs but not out of many other fluxes, such as FeAs, have been investigated. X-ray powder diffraction found that NaAs synthesized for the growth of RFeAsO superconductors has monoclinic LiAs structure. Thermal analysis confirmed that NaAs melts congruently at about 600 °C. The ability to extract RFeAsO crystals from this NaAs flux suggests that NaAs has a significant oxygen solubility, possibly due to the formation of the ternary compound NaAsO2, and enough oxygen diffusivity to transport solute to the growth front. Oxygen solubility and diffusivity are two important factors in searching for an alternative environmentally benign flux for the growth of RFeAsO superconductors.
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81.10.Fq Growth from melts; zone melting and refining
61.66.Fn Inorganic compounds
74.70.Xa Pnictides and chalcogenides

Cation-ordering effects in the single layered manganite La2/3Sr4/3MnO4

B. B. Nelson-Cheeseman, A. B. Shah, T. S. Santos, S. D. Bader, J.-M. Zuo, and A. Bhattacharya

Appl. Phys. Lett. 98, 072505 (2011); http://dx.doi.org/10.1063/1.3554387 (3 pages) | Cited 4 times

Online Publication Date: 16 February 2011

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Epitaxial La1−xSrxMnO3⋅SrO (x = 1/3) films were synthesized as random alloys and cation-ordered analogs to probe how cation ordering affects the properties of a two dimensional manganite. The films show evidence for a spin glass like phase below 20 K and weak ferromagnetic ordering up to 130 K. There is a dramatic difference in magnetic anisotropy and the low temperature transport mechanism depending on the cation order, which is consistent with differences in Mn 3d orbital occupancies. This work indicates that cation ordering can significantly alter the Mn 3d orbital ground state in these correlated electron systems.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Ng Insulators
75.50.Lk Spin glasses and other random magnets

Phonon softening induced by striped antiferromagnetic order in LiFeAs

B. Li, Z. W. Xing, and M. Liu

Appl. Phys. Lett. 98, 072506 (2011); http://dx.doi.org/10.1063/1.3555457 (3 pages) | Cited 3 times

Online Publication Date: 16 February 2011

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Using first-principles calculations in a supercell model with structural optimization, we investigate the magnetic ground state of LiFeAs and its phonon spectrum. The obtained magnetic ground state is the marginal striped antiferromagnetic state with partial structural relaxations. It is found that the anisotropic spin-lattice coupling in LiFeAs results in phonon softening of Fe–As atomic motion and so enhances the electron-phonon coupling. As a result, the electron-phonon interactions through the spin channel play an important role in the superconductivity of LiFeAs.
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74.25.Kc Phonons
63.20.kd Phonon-electron interactions
75.30.Ds Spin waves
71.15.-m Methods of electronic structure calculations

Stochastic resonance of a domain wall in a stripe with two pinning sites

Eduardo Martinez, Giovanni Finocchio, and Mario Carpentieri

Appl. Phys. Lett. 98, 072507 (2011); http://dx.doi.org/10.1063/1.3556314 (3 pages) | Cited 4 times

Online Publication Date: 17 February 2011

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We report on the observation of stochastic resonance phenomenon of a single domain wall in a ferromagnetic stripe with two pinning sites. Under a weak oscillating field, the wall performs irregular transitions between both constrictions in the presence of thermal fluctuations. Ours results indicate that synchronized wall transitions with the driving field can be achieved at the optimal level of noise. The stochastic resonance is quantified by computing the output signal power as a function of temperature. The analysis points out that this system could be used to design well-controlled amplification devices, which could find application as nanodetectors.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
02.50.Fz Stochastic analysis
75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
05.40.Ca Noise

Investigation of critical behavior in Pr0.55Sr0.45MnO3 by using the field dependence of magnetic entropy change

Jiyu Fan, Li Pi, Lei Zhang, Wei Tong, Langsheng Ling, Bo Hong, Yangguang Shi, Weichun Zhang, Di Lu, and Yuheng Zhang

Appl. Phys. Lett. 98, 072508 (2011); http://dx.doi.org/10.1063/1.3554390 (3 pages) | Cited 7 times

Online Publication Date: 17 February 2011

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One method of calculating critical exponents based on the field dependence on magnetic entropy change was applied to study critical behavior in Pr0.55Sr0.45MnO3. By using the obtained critical exponents, the modified Arrott plot [ A. Arrott and J. E. Noakes, Phys. Rev. Lett. 19, 786 (1967) ] is consistent with that by using conventional method. The calculated critical exponents not only obey the scaling theory, but also inosculate the deduced results from the Kouvel–Fisher method [ J. S. Kouvel and M. E. Fisher, Phys. Rev. 136, A1626 (1964) ]. It eliminates the drawback due to utilization of multistep nonlinear fitting in a conventional manner. Therefore, this means can be applied to investigate critical behavior.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.60.fh Studies of specific substances in the critical region
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Dipolar ferromagnetic phase transition in Fe3O4 nanoparticle arrays observed by Lorentz microscopy and electron holography

Kazuo Yamamoto, Charles R. Hogg, Saeki Yamamuro, Tsukasa Hirayama, and Sara A. Majetich

Appl. Phys. Lett. 98, 072509 (2011); http://dx.doi.org/10.1063/1.3556562 (3 pages) | Cited 9 times

Online Publication Date: 17 February 2011

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Dipolar ferromagnetism formed in Fe3O4 nanoparticle arrays is revealed by Fresnel Lorentz microscopy and electron holography. Dipolar domain walls do not lie preferentially along macrograin boundaries but depend on the overall shape of the assembly, meaning magnetostatic energy dominates. The domain structures are imaged at different temperatures for both monolayer and bilayer arrays. The domain wall contrast in the monolayer region is visible until 575 °C, and the magnetic order parameter steeply drops toward the temperature. In the bilayer region, finer and more complicated domains are formed.
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75.75.-c Magnetic properties of nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Mm Grain and twin boundaries
75.70.Ak Magnetic properties of monolayers and thin films
75.75.Fk Domain structures in nanoparticles
75.60.Ch Domain walls and domain structure

Enhanced magnetization drift velocity and current polarization in (CoFe)1−xGex alloys

M. Zhu, B. D. Soe, R. D. McMichael, M. J. Carey, S. Maat, and J. R. Childress

Appl. Phys. Lett. 98, 072510 (2011); http://dx.doi.org/10.1063/1.3554755 (3 pages) | Cited 2 times

Online Publication Date: 17 February 2011

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A spin-wave Doppler technique is used to measure the drift velocity of the magnetization in current-carrying (CoFe)1−xGex alloys. For a current density of 1011 A/m2, we obtain a large enhancement of drift velocity with increased Ge concentration from 3.1±0.2 m/s for CoFe to 8.2±0.6 m/s for (CoFe)0.7Ge0.3. Interpretation of these values yields current polarization increasing from 0.84±0.04 to 0.95±0.05 as the Ge doping increases. While both spin-dependent conductivities decrease with increasing Ge concentration, the maximum in polarization is associated with a stronger relative change in the minority spin conductivity.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves

Quantum-mechanical method for estimating ion distributions in spinel ferrites

G. D. Tang, D. H. Ji, Y. X. Yao, S. P. Liu, Z. Z. Li, W. H. Qi, Q. J. Han, X. Hou, and D. L. Hou

Appl. Phys. Lett. 98, 072511 (2011); http://dx.doi.org/10.1063/1.3553774 (3 pages) | Cited 5 times

Online Publication Date: 17 February 2011

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A quantum-mechanical method for estimating the cation distribution in spinel ferrites is proposed, by which the ionization energy of the cations and the Pauli repulsion energy is considered, together with the magnetic ordered energy and the tendency toward charge density balance. Using this method, not only can the difference between the observed and the traditional theoretical magnetic moments of the spinel structure ferrites MFe2O4 (M = Mn,Fe,Co,Ni,Cu) be explained, but also the dependence of the magnetic moments of the ferrites M1−xZnxFe2O4 (M = Mn,Fe,Co,Ni,Cu) on the doping level x can be fitted.
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61.72.up Other materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Gg Ferrimagnetics

Effect of resistance-area product on spin-transfer switching in MgO-based magnetic tunnel junction memory cells

Z. M. Zeng, P. Khalili Amiri, G. Rowlands, H. Zhao, I. N. Krivorotov, J.-P. Wang, J. A. Katine, J. Langer, K. Galatsis, K. L. Wang, and H. W. Jiang

Appl. Phys. Lett. 98, 072512 (2011); http://dx.doi.org/10.1063/1.3556615 (3 pages) | Cited 4 times

Online Publication Date: 18 February 2011

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We use ultrafast current-induced switching measurements to study spin-transfer switching performance metrics, such as write energy per bit (EW) and switching current density (Jc), as a function of resistance-area product (RA) (hence MgO thickness) in magnetic tunnel junction cells used for magnetoresistive random access memory (MRAM). EW increases with RA, while Jc decreases with increasing RA for both switching directions. The results are discussed in terms of RA optimization for low write energy and current drive capability (hence density) of the MRAM cells. Switching times <2 ns and write energies <0.3 pJ are demonstrated for 135 nm×65 nm CoFeB/MgO/CoFeB devices.
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85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
85.75.Dd Magnetic memory using magnetic tunnel junctions
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Enhanced multiferroic properties of single-phase BiFeO3 bulk ceramics by Ho doping

Nari Jeon, Dibyaranjan Rout, Ill Won Kim, and Suk-Joong L. Kang

Appl. Phys. Lett. 98, 072901 (2011); http://dx.doi.org/10.1063/1.3552682 (3 pages) | Cited 21 times

Online Publication Date: 14 February 2011

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Dense single-phase BiFeO3 and Bi0.9Ho0.1FeO3 ceramics were prepared by the solid-state reaction method. With Ho doping, the remnant polarization of BiFeO3 was enhanced and the switching characteristics improved at low electric fields. Ho doping increased the breakdown voltage with a reduction of the leakage current while mitigating the remnant polarization at high electric fields. These results can explain conflicting findings regarding the effects of rare-earth doping on remnant polarization. Bi0.9Ho0.1FeO3 exhibited peculiar double hysteresis looplike magnetization-magnetic field curves with a much enhanced remnant magnetization. These improved properties obtained by Ho doping demonstrate the possibility of enhancing the multiferroic applicability of BiFeO3.
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81.20.-n Methods of materials synthesis and materials processing
77.80.Fm Switching phenomena
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Grain boundary assisted degradation and breakdown study in cerium oxide gate dielectric using scanning tunneling microscopy

K. Shubhakar, K. L. Pey, S. S. Kushvaha, S. J. O’Shea, N. Raghavan, M. Bosman, M. Kouda, K. Kakushima, and H. Iwai

Appl. Phys. Lett. 98, 072902 (2011); http://dx.doi.org/10.1063/1.3553190 (3 pages) | Cited 5 times

Online Publication Date: 14 February 2011

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The presence of grain boundaries (GBs) in polycrystalline high-κ (HK) gate dielectric materials affects the electrical performance and reliability of advanced HK based metal-oxide-semiconductor devices. It is important to study the role of GB in stress-induced-leakage current (SILC) degradation and time-dependent dielectric breakdown of polycrystalline HK gate stacks. In this work, we present nanoscale localized electrical study and uniform stressing analysis comparing the electrical conduction properties at grain and GB locations for blanket cerium oxide (CeO2)-based HK thin films using scanning tunneling microscopy. The results clearly reveal higher SILC degradation rate at GB sites and their vulnerability to early percolation, supporting the phenomenon of GB-assisted HK gate dielectric degradation and breakdown.
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73.61.Ng Insulators
77.55.df For silicon electronics
61.72.Mm Grain and twin boundaries
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