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8 Aug 2005

Volume 87, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 061103 (2005); http://dx.doi.org/10.1063/1.2008357 (3 pages)

Y. C. Zhong, S. A. Zhu, H. M. Su, H. Z. Wang, J. M. Chen, Z. H. Zeng, and Y. L. Chen
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Gold based bulk metallic glass

Jan Schroers, Boonrat Lohwongwatana, William L. Johnson, and Atakan Peker

Appl. Phys. Lett. 87, 061912 (2005); http://dx.doi.org/10.1063/1.2008374 (3 pages) | Cited 80 times

Online Publication Date: 3 August 2005

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Gold-based bulk metallic glass alloys based on Au–Cu–Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5 mm in the best glassformer. Au49Ag5.5Pd2.3Cu26.9Si16.3 has a liquidus temperature of 644 K, a glass transition temperature of 401 K, and a supercooled liquid region of 58 K. The Vickers hardness of the alloys in this system is ∼ 350 Hv, twice that of conventional 18-karat crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry.
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81.05.Kf Glasses (including metallic glasses)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Micro-x-ray absorption near-edge structure imaging for detecting metallic Mn in GaN

G. Martínez-Criado, A. Somogyi, A. Homs, R. Tucoulou, and J. Susini

Appl. Phys. Lett. 87, 061913 (2005); http://dx.doi.org/10.1063/1.1989446 (3 pages) | Cited 11 times

Online Publication Date: 3 August 2005

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In this study, we report the application of a synchrotron radiation microprobe to the analysis of Mn valencies in GaN. X-ray absorption near-edge structure (XANES) images taken around Mn K-edge in fluorescence detection mode reveal the concentration of oxidation states of Mn centers. By fitting the XANES curve for each point of the image, the distributions of the Mn0, Mn2+, and Mn3+ oxidation states are obtained. At low Mn concentrations, there is a homogeneous mixture of Mn2+ and Mn3+ centers, while at high Mn content strong spatial-dependent Mn0 and Mn2+ distributions characterize the XANES maps. In a supplementary way with respect to Mn2+, the Mn0 pattern suggests the presence of specific cluster-like features, indicating surface segregation of metallic Mn centers.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.70.Dm X-ray absorption spectra
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors

Photoinduced changes of surface order in coumarin side-chain polymer films used for liquid crystal photoalignment

G. Bergmann, P. O. Jackson, J. H. C. Hogg, T. Stirner, M. O’Neill, W. L. Duffy, S. M. Kelly, and G. F. Clark

Appl. Phys. Lett. 87, 061914 (2005); http://dx.doi.org/10.1063/1.2009070 (3 pages) | Cited 1 time

Online Publication Date: 3 August 2005

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Specular x-ray reflectivity probes morphological changes in a crosslinkable coumarin photoalignment polymer film resulting from ultraviolet irradiation. An ordered surface layer with density oscillations compatible with planar side-chain alignment is obtained before irradiation. The ordering is enhanced in the early stages of crosslinking. This is attributed to the photoinduced increase of mobility of the side-chains resulting from the creation of free volume by the crosslinking process. The expansion of the thin film confirms that free volume is created. The surface ordering decreases with prolonged ultraviolet irradiation because of increased material viscosity resulting from a high crosslinked density. The implications of surface ordering on liquid crystal photoalignment are discussed.
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61.30.Vx Polymer liquid crystals
61.25.H- Macromolecular and polymers solutions; polymer melts
82.35.-x Polymers: properties; reactions; polymerization
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
68.47.Mn Polymer surfaces
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds
66.20.-d Viscosity of liquids; diffusive momentum transport

Experimental and theoretical evidence for vacancy-clustering-induced large voids in Czochralski-grown germanium crystals

S. Hens, J. Vanhellemont, D. Poelman, P. Clauws, I. Romandic, A. Theuwis, F. Holsteyns, and J. Van Steenbergen

Appl. Phys. Lett. 87, 061915 (2005); http://dx.doi.org/10.1063/1.2009830 (2 pages) | Cited 10 times

Online Publication Date: 3 August 2005

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Optical inspection of polished Czochralski-grown Ge wafers typically reveals the presence of surface pits similar to the Crystal Originated Particles (COP’s) observed in silicon but in a wider variety of sizes and shapes. Computer simulation of vacancy clustering during the Cz germanium crystal growth suggests that the surface pits originate from large voids formed by the diffusion-limited clustering of an excess of vacancies.
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61.72.J- Point defects and defect clusters
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Conducting In-doped CdTe oxide thin films grown by pulsed-laser deposition

R. Castro-Rodríguez, J. L. Peña, F. Leccabue, B. E. Watts, and E. Melioli

Appl. Phys. Lett. 87, 061916 (2005); http://dx.doi.org/10.1063/1.2005391 (3 pages) | Cited 2 times

Online Publication Date: 3 August 2005

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Conducting transparent oxide semiconductor In-doped CdTe oxide (ICTO) thin films ( ∼ 200 nm thick) have been deposited by pulsed-laser deposition on glass substrates without a postdeposition anneal. The electrical, structural, and optical properties of these films have been investigated as a function of O2 partial pressures during the deposition. Films were deposited at substrate temperature of 420 °C in oxygen partial pressures between 15 and 55 mTorr. The resistivity is very sensitive to the oxygen deposition pressure; at 28.5 mTorr the films show electrical resistivities as low as 9.4×10−3 Ω cm, an average visible transmittance of ∼ 75.5%, and an optical band gap of 2.74 eV.
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81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Bulk-like pentacene epitaxial films on hydrogen-terminated Si(111)

Toshihiro Shimada, Hiroyuki Nogawa, Tetsuya Hasegawa, Ryusuke Okada, Hisashi Ichikawa, Keiji Ueno, and Koichiro Saiki

Appl. Phys. Lett. 87, 061917 (2005); http://dx.doi.org/10.1063/1.2008371 (3 pages) | Cited 11 times

Online Publication Date: 4 August 2005

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The epitaxial growth of pentacene on hydrogen-terminated Si(111) is reported. Reflection high energy electron diffraction (RHEED) revealed that the crystal packing resembles that in the bulk crystal even at a monolayer thickness, which was maintained in multilayers. A ripening effect was clearly observed by atomic force microscopy (AFM). These results are important to obtain oriented crystalline films of pentacene combined with silicon microdevices with reduced defect densities.
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81.05.Hd Other semiconductors
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Atomic structure in Zr70Cu29Pd1 metallic glass

L. Yang, J. Z. Jiang, T. Liu, T. D. Hu, and T. Uruga

Appl. Phys. Lett. 87, 061918 (2005); http://dx.doi.org/10.1063/1.2009827 (3 pages) | Cited 14 times

Online Publication Date: 4 August 2005

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Local atomic structures of Pd, Cu, and Zr atoms in an as-prepared Zr70Cu29Pd1 glassy alloy and the annealed samples containing icosahedral quasicrystal have been investigated by Pd, Cu, and Zr K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that Cu and Zr atoms have an icosahedral atomic surrounding. Cu atoms could locate at both center position and shell sites while Zr atoms most likely occupy the shell sites of icosahedron. Pd atoms neither substitute Zr atoms nor Cu atoms. They sit at octahedral interstices, which link up icosahedron and promote the growth of icosahedron into long-range-order icosahedral quasicrystal in the ternary Zr70Cu29Pd1 glassy alloy during annealing treatment.
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61.43.Fs Glasses
78.70.Dm X-ray absorption spectra
81.40.Gh Other heat and thermomechanical treatments

Ag9TlTe5: A high-performance thermoelectric bulk material with extremely low thermal conductivity

Ken Kurosaki, Atsuko Kosuga, Hiroaki Muta, Masayoshi Uno, and Shinsuke Yamanaka

Appl. Phys. Lett. 87, 061919 (2005); http://dx.doi.org/10.1063/1.2009828 (3 pages) | Cited 41 times

Online Publication Date: 4 August 2005

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We studied a high-performance thermoelectric material whose chemical formula is Ag9TlTe5. Ag9TlTe5 is simple and easy to prepare. Its highest dimensionless figure of merit (ZT) value is 1.23, obtained at 700 K. The values of individual thermoelectric properties at 700 K are 2.63×10−4 Ω m for electrical resistivity, 319 μV K−1 for Seebeck coefficient, and 0.22 W m−1 K−1 for thermal conductivity. Ag9TlTe5 is a unique material combining extremely low thermal conductivity and relatively low electrical resistivity.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Determination of thermal and optical parameters of melanins by photopyroelectric spectroscopy

J. E. de Albuquerque, C. Giacomantonio, A. G. White, and P. Meredith

Appl. Phys. Lett. 87, 061920 (2005); http://dx.doi.org/10.1063/1.2009833 (3 pages) | Cited 8 times

Online Publication Date: 4 August 2005

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Photopyroelectric spectroscopy (PPE) was used to study the thermal and optical properties of melanins. The photopyroelectric intensity signal and its phase were independently measured as a function of wavelength and chopping frequency for a given wavelength in the saturation part of the PPE spectrum. Equations for both the intensity and the phase of the PPE signal were used to fit the experimental results. From these fits we obtained for the first time, with great accuracy, the thermal diffusivity coefficient, the thermal conductivity, and the specific heat of the samples, as well as a value for the condensed phase optical gap, which we found to be 1.70 eV.
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87.14.-g Biomolecules: types
87.15.M- Spectra of biomolecules
87.15.Vv Diffusion

Rapid stress-driven grain coarsening in nanocrystalline Cu at ambient and cryogenic temperatures

Kai Zhang, J. R. Weertman, and J. A. Eastman

Appl. Phys. Lett. 87, 061921 (2005); http://dx.doi.org/10.1063/1.2008377 (3 pages) | Cited 97 times

Online Publication Date: 5 August 2005

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There have been long-standing concerns about the stability of the internal structure of nanocrystalline metals. In this letter we examine grain growth in nanocrystalline Cu under the microhardness indenter, examining the influence of temperature of indentation and sample purity. Surprisingly, it is found that grain coarsening is even faster at cryogenic temperatures than at room temperature. Sample purity is seen to play an important role in determining the rate of grain growth. Fast grain coarsening can affect the outcome of mechanical tests, especially if they involve large stresses and high-purity samples.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness

Tunable uniaxial vs biaxial in-plane strain using compliant substrates

Haizhou Yin, R. L. Peterson, K. D. Hobart, S. R. Shieh, T. S. Duffy, and J. C. Sturm

Appl. Phys. Lett. 87, 061922 (2005); http://dx.doi.org/10.1063/1.2006215 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2005

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In this letter, the relaxation of strained rectangular islands on compliant substrates is used to achieve semiconductor thin films with either uniaxial stress or uniaxial strain in the plane of the film over an area of tens of microns. The work is demonstrated using silicon and silicon–germanium alloy single-crystal thin films, with uniaxial strain values approaching 1%. The biaxially strained SiGe or SiGe/Si films on borophosphorosilicate glass (BPSG) were fabricated by a wafer bonding and layer transfer process. When the viscosity of BPSG drops at high temperatures for short times, films patterned in a rectangular shape can move laterally to relieve stress only in one in-plane direction. Thus one can tailor the strain from biaxial to uniaxial in the thin films.
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81.05.Cy Elemental semiconductors
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.A- Nucleation and growth
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Friction transfer deposition of ordered conjugated polymer nanowires and transistor fabrication

S. P. Li, C. J. Newsome, D. M. Russell, T. Kugler, M. Ishida, and T. Shimoda

Appl. Phys. Lett. 87, 062101 (2005); http://dx.doi.org/10.1063/1.2009063 (3 pages) | Cited 15 times

Online Publication Date: 1 August 2005

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Monodisperse, ordered conjugated polymer nanowires were deposited by friction-transfer technique. Films that comprise such ordered polymer nanowires show a strong optical and electronic anisotropy due to the high compaction of molecule chains in the individual nanowires. Field-effect transistors that were fabricated using poly[9,9-dioctylfluorene-co-bithiophene(F8T2)] nanowires exhibit a field-effect mobility of 3.5×10−2 cm2 V−1 s−1 along the wire direction, which is much higher than the mobility value (5×10−3 cm2 V−1 s−1) obtained in transistors with spin-coated F8T2.
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81.05.Hd Other semiconductors
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.30.Tv Field effect devices
81.07.Vb Quantum wires
68.55.A- Nucleation and growth
73.63.Nm Quantum wires
78.67.Lt Quantum wires
78.66.Qn Polymers; organic compounds

Observation of hysteretic magnetoresistance in Mn-doped GaN nanowires with the mesoscopic Co and Ti/Au contacts

Seong-Eok Han, Hwangyou Oh, Ju-Jin Kim, Han-Kyu Seong, and Heon-Jin Choi

Appl. Phys. Lett. 87, 062102 (2005); http://dx.doi.org/10.1063/1.2009832 (3 pages) | Cited 9 times

Online Publication Date: 2 August 2005

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We have studied the spin dependent tunneling properties of Mn-doped GaN nanowires with ferromagnetic Co contacts. The magnetoresistances were measured between two ferromagnetic Co electrodes, or Co and Ti/Au electrodes through Mn-doped GaN nanowires. The magnetoresistances of nanowire with the Co electrode indicate hysteretic behaviors, which are commonly observed in tunnel magnetoresistance devices. The magnetoresistance ratio increases from −0.6% at 20 K to −9.4% at 1.74 K. It is believed that the hysteretic magnetoresistances originate from the tunnel magnetoresistance effect between the ferromagnetic phases of nanowire and Co electrode.
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73.63.Bd Nanocrystalline materials
75.50.Pp Magnetic semiconductors
72.25.Mk Spin transport through interfaces
75.47.−m

Two-dimensional electrons at a cleaved semiconductor surface: Observation of the quantum Hall effect

Yukihide Tsuji, Toshimitsu Mochizuki, and Tohru Okamoto

Appl. Phys. Lett. 87, 062103 (2005); http://dx.doi.org/10.1063/1.2009811 (3 pages) | Cited 9 times

Online Publication Date: 2 August 2005

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Low-temperature in-plane magnetotransport measurements have been performed on adsorbate-induced electron systems formed at in situ cleaved surfaces of p-type InAs. The Ag-coverage dependence of the surface electron density strongly supports a simple model based on a surface donor level lying above the conduction-band minimum. The observations of the quantized Hall resistance and zero longitudinal resistivity demonstrate the perfect two dimensionality of the surface electron system. We also observed the Rashba effect due to the strong asymmetry of the confining potential well.
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68.47.Fg Semiconductor surfaces
73.43.-f Quantum Hall effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.63.-b Electronic transport in nanoscale materials and structures
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.At Surface states, band structure, electron density of states

Assemblies of silicon nanoparticles roll up into flexible nanotubes

Sahraoui Chaieb, Munir H. Nayfeh, and Adam D. Smith

Appl. Phys. Lett. 87, 062104 (2005); http://dx.doi.org/10.1063/1.2009051 (3 pages) | Cited 2 times

Online Publication Date: 3 August 2005

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When a colloidal dispersion of fluorescent 1 nm silicon nanoparticles in alcohol is subjected to an electric field, the nanoparticles are driven to the surface of the anode substrate, where they form a thin film. Upon drying, the film delaminates from the surface of the anode and rolls up into ∼ 100 μm long nanotube. Nanotube diameters ranging from 0.2 to 5 μm with wall thicknesses in the range of 20–40 nm have been achieved. By applying a force on the tubes using atomic force microscopy, we estimate Young’s modulus of the film and find it to be close to that of rubber. We also study the crystalline structure of the film using electron diffraction and find it to be quartzlike.
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61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
68.37.−d
81.07.−b
81.16.−c

Negative-U property of oxygen vacancy in cubic HfO2

Y. P. Feng, A. T. L. Lim, and M. F. Li

Appl. Phys. Lett. 87, 062105 (2005); http://dx.doi.org/10.1063/1.2009826 (3 pages) | Cited 25 times

Online Publication Date: 3 August 2005

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Oxygen vacancy in cubic HfO2 was investigated using first-principles calculation based on density functional theory and generalized gradient approximation. Five different charge states (V++, V+, V0, V−, and V−−) were investigated. It was found that the oxygen vacancy in HfO2 has negative-U behavior and it is energetically favorable for the vacancy to trap two electrons or two holes when the respective charges are injected into the oxide, due to large electron-lattice interaction. Therefore, oxygen vacancy is a main source of charge traps in both n- and p-type metal-oxide-semiconductor field-effect transistors based on HfO2, and reducing such defects will be useful in limiting charge trapping and in improving the quality of the high-k dielectric in modern complementary metal-oxide semiconductor technology.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.J- Point defects and defect clusters
85.30.Tv Field effect devices

Submicron periodic poling and chemical patterning of GaN

S. Pezzagna, P. Vennéguès, N. Grandjean, A. D. Wieck, and J. Massies

Appl. Phys. Lett. 87, 062106 (2005); http://dx.doi.org/10.1063/1.2009839 (3 pages) | Cited 12 times

Online Publication Date: 5 August 2005

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Periodic polarity (PePo) GaN films are grown by molecular-beam epitaxy. A high Mg doping is used to reverse the film polarity from Ga to N. An etching step is then performed to define the PePo pattern. Ultrasharp inversion domain boundaries between Ga- and N-polar domains are shown by transmission electron microscopy. Moreover, it is demonstrated that three-dimensional (3D) patterned Ga-polarity GaN films can be obtained from these PePo samples by a simple wet chemical etching procedure. When combined with a focused ion beam (FIB) to define the initial PePo template, periodic poling as well as chemical 3D patterning is demonstrated down to the nanometer scale.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.16.Rf Micro- and nanoscale pattern formation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
61.72.uj III-V and II-VI semiconductors
68.37.Lp Transmission electron microscopy (TEM)
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Magnetic property investigations on Mn-doped ZnO Layers on sapphire

A. Che Mofor, A. El-Shaer, A. Bakin, A. Waag, H. Ahlers, U. Siegner, S. Sievers, M. Albrecht, W. Schoch, N. Izyumskaya, V. Avrutin, S. Sorokin, S. Ivanov, and J. Stoimenos

Appl. Phys. Lett. 87, 062501 (2005); http://dx.doi.org/10.1063/1.2007864 (3 pages) | Cited 54 times

Online Publication Date: 1 August 2005

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The need for diluted magnetic semiconductors has stimulated research on Mn-doped ZnO. However, the type of magnetic coupling (ferro/para) in ZnMnO remains an issue of debate. We have investigated the magnetic properties of Mn-doped ZnO layers grown by molecular beam epitaxy. Some samples showed a hysteresis with remnant magnetization on the order of 10−5 emu, thus eventually suggesting ferromagnetism. We observed that the critical influence of the substrate substantially affects magnetic property measurements. This has to be taken into account in order to clearly confirm ferromagnetism. In our case, after subtraction of the substrate effect, there is no evidence of a ferromagnetic behavior for the ZnMnO samples.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
81.05.Dz II-VI semiconductors

Push-pull mode magnetostrictive/piezoelectric laminate composite with an enhanced magnetoelectric voltage coefficient

Shuxiang Dong, Jungyi Zhai, Feiming Bai, Jie-Fang Li, and D. Viehland

Appl. Phys. Lett. 87, 062502 (2005); http://dx.doi.org/10.1063/1.2007868 (3 pages) | Cited 69 times

Online Publication Date: 1 August 2005

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A magnetoelectric (ME) laminate composite consisting of a symmetric longitudinally poled piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 crystal and two longitudinally magnetized magnetostrictive Tb1−xDyxFe2 layers has been developed that has a notably superior ME voltage coefficient, relative to previous laminate configurations. The symmetric nature of the longitudinally poled piezoelectric layer allows for operation in a push-pull mode that optimizes elastic coupling between layers. Our small laminate has a giant ME voltage coefficient of ∼ 1.6 V/Oe at low frequencies, a significant enhancement of this coefficient to ∼ 20 V/Oe under resonance drive, and an exceptional low-level magnetic field sensitivity of ∼ 10−12 T at f = f0.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.80.+q Magnetomechanical effects, magnetostriction
77.65.-j Piezoelectricity and electromechanical effects

Spatially resolved observation of domain-wall propagation in a submicron ferromagnetic NOT-gate

Xiaobin Zhu, Dan A. Allwood, Gang Xiong, Russell P. Cowburn, and Peter Grütter

Appl. Phys. Lett. 87, 062503 (2005); http://dx.doi.org/10.1063/1.2009050 (3 pages) | Cited 8 times

Online Publication Date: 1 August 2005

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Domain-wall propagation under an external magnetic field in a submicron ferromagnetic ring integrated with a NOT-junction is investigated by magnetic force microscopy and micromagnetic modeling. Within a certain magnetic field range, one head-to-head or tail-to-tail domain wall propagates in the structure. Magnetic fields above this range cause nucleation of additional domain walls in the ring structure while fields below this range are not able to switch the NOT-junction magnetization. This explicitly demonstrates the magnetization reversal, operation, and failure modes of a magnetic NOT-junction.
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75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
68.37.Rt Magnetic force microscopy (MFM)
75.60.Jk Magnetization reversal mechanisms
84.30.Sk Pulse and digital circuits

Magnetic tuning of Fermi level for tunnel spintronics devices

Yu. G. Pogorelov, J. B. Sousa, and J. P. Araújo

Appl. Phys. Lett. 87, 062504 (2005); http://dx.doi.org/10.1063/1.2009049 (3 pages)

Online Publication Date: 2 August 2005

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Treating itinerant magnetism within the simplest two-subband Hubbard model, it is shown that the variation of the Fermi energy under applied magnetic field is inversely proportional to the spontaneous magnetization (when the latter is small). Hence, the variation is most pronounced at closeness to the critical Stoner condition, that is to the quantum critical point of ferromagnetic condition. The perspectives of this result for magnetic tuning of tunnel conductance in spintronics devices are discussed.
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75.10.Lp Band and itinerant models
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport

Alignment and analyses of MnBi/Bi nanostructures

K. Kang, L. H. Lewis, and A. R. Moodenbaugh

Appl. Phys. Lett. 87, 062505 (2005); http://dx.doi.org/10.1063/1.2008368 (3 pages) | Cited 8 times

Online Publication Date: 3 August 2005

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A Mn5Bi95 alloy was rapidly solidified into a mixture of nanocrystalline Bi and metastable Bi(Mn). Heating the ribbons to temperature T = 525 K in a dc magnetic field causes formation and c-axis alignment of low-temperature phase (LTP) MnBi nanorods along the applied field direction. Nanorod alignment increases with increased magnetic field, with a calculated alignment half-angle of 47° for a sample heated to 520 K at 50 kOe. In situ magnetization changes suggest that nanorod alignment is achieved by rotation of MnBi particles. Particle alignment enables the measurement of the MnBi nanorod spin reorientation temperature of 100 K, the same as its bulk counterpart.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.30.Fb Solidification

Ferromagnetic ordering in nanostructured Mn-doped InP

P. Poddar, Y. Sahoo, H. Srikanth, and P. N. Prasad

Appl. Phys. Lett. 87, 062506 (2005); http://dx.doi.org/10.1063/1.2009840 (3 pages) | Cited 17 times

Online Publication Date: 3 August 2005

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We report the observation of ferromagnetic ordering at 25 K in a diluted magnetic semiconductor (DMS) nanoparticle system: In0.9Mn0.1P, sized 3 nm. These particles were synthesized using a novel nanochemical technique without using any external surfactant. Structural and elemental characterizations established the occurrence of the zinc-blende phase of the DMS without any separate or induced impurity phase. A robust onset of ferromagnetic order is observed in magnetization measurements at around 25 K with blocked state behavior below 15 K characteristic of magnetic nanoparticles. The system shows strong frequency dependence of the susceptibility, similar to the behavior observed for spin glasses. Reversible transverse susceptibility experiments done using a resonant radio-frequency (rf) method reveal a strong temperature-dependent effective anisotropy.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Effect of bias on indirect exchange within magnetic nanostructures

V. I. Kozub and V. Vinokur

Appl. Phys. Lett. 87, 062507 (2005); http://dx.doi.org/10.1063/1.2009810 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2005

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We formulate a theory of a reversible switching of the magnetic state of magnetic multilayers embedded in the metallic nanoconstriction by the external bias. The switching is related to the effect of strongly nonequilibrium electron distribution existing in the biased nanoconstriction on the indirect exchange coupling between the magnetic layers.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.30.Et Exchange and superexchange interactions
71.70.Gm Exchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.-d Domain effects, magnetization curves, and hysteresis
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Direct observation of a fully strained dead layer at Ba0.7Sr0.3TiO3/SrRuO3 interface

J. Q. He, E. Vasco, C. L. Jia, and R. H. Wang

Appl. Phys. Lett. 87, 062901 (2005); http://dx.doi.org/10.1063/1.2008372 (3 pages) | Cited 19 times

Online Publication Date: 3 August 2005

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Epitaxial SrRuO3/Ba0.7Sr0.3TiO3 (BST)/SrRuO3 thin film capacitors were prepared on SrTiO3 substrates by pulsed laser deposition. The structures of stacked BST films with different thicknesses were investigated by transmission electron microscopy. A distinctive layer of about 3 nm of thickness was identified within BST films thicker than 9 nm at the interface with the SrRuO3 bottom electrode. The distinctive layer is misfit dislocation-free showing pseudoconstant lattice parameters. Misfit dislocations are formed at the interface between the distinctive layer and the BST film bulk layer relaxing the latter as the film thickness increases. The effect of the distinctive layer on the system dielectric response is discussed within the framework of an interfacial dead-layer model.
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77.55.-g Dielectric thin films
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