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13 Nov 2006

Volume 89, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 89, 202101 (2006); http://dx.doi.org/10.1063/1.2388049 (3 pages)

J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur, and G. J. Salamo
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Enhancement of ferromagnetic properties of NiO:Fe thin film by Li doping

Yuan-Hua Lin, Rongjuan Zhao, Ce-Wen Nan, Minghao Ying, M. Kobayashi, Y. Ooki, and A. Fujimori

Appl. Phys. Lett. 89, 202501 (2006); http://dx.doi.org/10.1063/1.2388130 (3 pages) | Cited 11 times

Online Publication Date: 13 November 2006

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Li and Fe codoped NiO thin films (LixNi0.98−xFe0.02O, x = 0–0.05) were obtained by a sol-gel spin-coating method on silicon substrates. Phase composition and microstructure analysis indicated that the film samples contained 20–30 nm sized NiO particles. With increasing Li-doping concentration, the current density of the films increased due to the increase of hole carriers. Magnetization measurements revealed that all the thin films showed room-temperature ferromagnetic properties and could be enhanced by Li doping, which should be due to the fact that hole doping makes ferromagnetic coupling interactions between the hole carriers and localized Fe 3d spins more efficient.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials

Over 70% tunneling magnetoresistance at room temperature for a CoFe and AlOx based magnetic tunnel junction

J. Joshua Yang, Chengxiang Ji, Y. Austin Chang, Xianglin Ke, and M. S. Rzchowski

Appl. Phys. Lett. 89, 202502 (2006); http://dx.doi.org/10.1063/1.2387568 (3 pages) | Cited 19 times

Online Publication Date: 13 November 2006

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More than 70% tunneling magnetoresistance (TMR) ratio has been observed at room temperature for a CoFe and AlOx based magnetic tunnel junction. The annealing of the epitaxial bottom electrode, Si (001)/Ag fcc (200)/Co84Fe16 bcc (200), at 400 °C prior to fabricating the tunnel barrier and the upper electrode is crucial for achieving this high TMR ratio. Moreover a high output voltage could be obtained for this magnetic tunnel junction due to its high V1/2, the bias voltage at which the TMR ratio is reduced to half of that near the zero bias. The rationale for obtaining this high TMR ratio is discussed, and there are reasons to believe that the TMR ratio for this junction could be further improved.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.47.Pq Other materials
75.50.Bb Fe and its alloys

High-pressure synthesis of giant magnetostrictive PrxTb1−xFe1.9 alloys

Y. G. Shi, S. L. Tang, R. L. Wang, H. L. Su, Z. D. Han, L. Y. Lv, and Y. W. Du

Appl. Phys. Lett. 89, 202503 (2006); http://dx.doi.org/10.1063/1.2387865 (3 pages) | Cited 13 times

Online Publication Date: 13 November 2006

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PrxTb1−xFe1.9 (0 ⩽ x ⩽ 1) magnetostrictive alloys with cubic Laves phase have been synthesized by a high-pressure synthesis method. Crystal structure, magnetic properties, magnetocrystalline anisotropy, and the magnetostriction of PrxTb1−xFe1.9 (0 ⩽ x ⩽ 1) alloys are investigated. Composition anisotropy compensation is realized in Pr0.9Tb0.1Fe1.9 alloy, which shows low magnetocrystalline anisotropy and a large magnetostriction value (λ‖−λ⊥ = 1497 ppm) at 13 kOe at room temperature. These characters suggest that Pr0.9Tb0.1Fe1.9 alloy may be a promising candidate for magnetostriction application.
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75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
61.66.Dk Alloys

Magnetic field processing to enhance critical current densities of MgB2 superconductors

S. X. Dou, W. K. Yeoh, O. Shcherbakova, J. Horvat, J. H. Kim, A. V. Pan, D. Wexler, Y. Li, W. X. Li, Z. M. Ren, P. Munroe, and J. Z. Cui

Appl. Phys. Lett. 89, 202504 (2006); http://dx.doi.org/10.1063/1.2388126 (3 pages) | Cited 11 times

Online Publication Date: 14 November 2006

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A magnetic field of up to 12 T was applied during the sintering process of pure MgB2 and carbon nanotube (CNT) doped MgB2 wires. The authors have demonstrated that magnetic field processing results in grain refinement, homogeneity, and enhancement in Jc(H) and Hirr. The extent of improvement in Jc increases with increasing field. The Jc for a 10 T field processed CNT doped sample increases by a factor of 3 at 10 K and 8 T and at 20 K and 5 T, respectively. Hirr for the 10 T field processed CNT doped sample reached 9 T at 20 K, which exceeded the best value of SiC doped MgB2 at 20 K. Magnetic field processing reduces the resistivity in CNT doped MgB2, straightens the entangled CNTs, and improves the adherence between CNTs and the MgB2 matrix.
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74.25.Sv Critical currents
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.35.Np Adhesion

Domain overlap in antiferromagnetically coupled [Co/Pt]/NiO/[Co/Pt] multilayers

A. Baruth, L. Yuan, J. D. Burton, K. Janicka, E. Y. Tsymbal, S. H. Liou, and S. Adenwalla

Appl. Phys. Lett. 89, 202505 (2006); http://dx.doi.org/10.1063/1.2388892 (3 pages) | Cited 17 times

Online Publication Date: 14 November 2006

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Antiferromagnetically coupled magnetic thin films with perpendicular anisotropy exhibit domain overlap regions originating from magnetostatic stray fields localized in the vicinity of the domain walls. Using high resolution magnetic force microscopy, the authors investigate these overlap regions in [Co/Pt]/NiO/[Co/Pt] multilayers with various strengths of the interlayer exchange coupling. They develop a simple model that provides a quantitative explanation of the formation of these regions and the relationship between the domain overlap width and the coupling strength. Their results are important for application of magnetic layered structures with perpendicular anisotropy in advanced magnetoresistive devices.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.50.Ee Antiferromagnetics

Swift-heavy-ion-irradiation-induced enhancement in electrical conductivity of chemical solution deposited La0.7Ba0.3MnO3 thin films

R. N. Parmar, J. H. Markna, D. G. Kuberkar, Ravi Kumar, D. S. Rana, Vivas C. Bagve, and S. K. Malik

Appl. Phys. Lett. 89, 202506 (2006); http://dx.doi.org/10.1063/1.2359291 (3 pages) | Cited 2 times

Online Publication Date: 14 November 2006

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Epitaxial thin films of La0.7Ba0.3MnO3 manganite, deposited using chemical solution deposition technique, were irradiated by 200 MeV Ag+15 ions with a maximum ion dose up to 1×1012 ions/cm2. Temperature and magnetic-field-dependent resistivity measurements on all the films (before and after irradiation) reveal a sustained decrease in resistivity with increasing ion dose. A maximum dose of 1×1012 ions/cm2 suppresses resistivity by factors of 3 and 10 at 330 K [insulator-metal (I-M) transition] and at 10 K, respectively. On the other hand, with increasing ion dose, the magnetoresistance enhances in the vicinity of I-M transition but decreases at low temperatures. These results, corroborated by surface morphology of films, suggest that the origin of such properties lies in the irradiation induced improved crystallinity and epitaxial orientation, enhanced connectivity between grains and conglomeration of grains, which result in better conductivity at grain boundaries.
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73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Magnetic properties of hydrogenated Li and Co doped ZnO nanoparticles

O. D. Jayakumar, I. K. Gopalakrishnan, K. Shashikala, S. K. Kulshreshtha, and C. Sudakar

Appl. Phys. Lett. 89, 202507 (2006); http://dx.doi.org/10.1063/1.2387877 (3 pages) | Cited 14 times

Online Publication Date: 15 November 2006

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The effect of hydrogenation on the magnetic properties of Zn0.85Co0.05Li0.10O nanoparticles is presented. It was found that the sample hydrided at room temperature (RT) showed weak ferromagnetism, while that hydrided at 400 °C showed robust ferromagnetism at room temperature. In both cases reheating the sample at 400 °C in air converts it back into the paramagnetic state completely. The characterization of samples by x-ray and electron diffraction showed that room temperature ferromagnetism observed in the samples hydrogenated at RT is intrinsic in nature, whereas that observed in the samples hydrogenated at 400 °C is partly due to the cobalt metal clusters.
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75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
81.40.Gh Other heat and thermomechanical treatments

Magnetoelectric exchange bias systems in spintronics

Xi Chen, Andreas Hochstrat, Pavel Borisov, and Wolfgang Kleemann

Appl. Phys. Lett. 89, 202508 (2006); http://dx.doi.org/10.1063/1.2388149 (3 pages) | Cited 37 times

Online Publication Date: 15 November 2006

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Magnetoelectric switching of perpendicular exchange bias is observed in a Co/Pt multilayer attached to single crystalline magnetoelectric antiferromagnetic Cr2O3(111). The exchange bias field HEB can be set to positive or negative values by applying an electric field Efr either parallel or antiparallel to the magnetic freezing field Hfr while cooling to below the Néel temperature. Based on this result, the antiferromagnetic spin state can be used as a medium for data storage. The authors propose magnetic random access memory cells and magnetic logic devices, which are purely voltage controlled.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Et Exchange and superexchange interactions
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
85.75.Bb Magnetic memory using giant magnetoresistance
84.30.Sk Pulse and digital circuits

Diluted magnetic semiconductors with high Curie temperature based on C1b compounds: CoTi1−xFexSb

Kristian Kroth, Benjamin Balke, Gerhard H. Fecher, Vadim Ksenofontov, Claudia Felser, and Hong-Ji Lin

Appl. Phys. Lett. 89, 202509 (2006); http://dx.doi.org/10.1063/1.2388876 (3 pages) | Cited 14 times

Online Publication Date: 15 November 2006

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Diluted magnetic semiconductors were prepared by substituting titanium in the semiconducting compound CoTiSb with iron. The structural, electronic, and magnetic properties of the pure and doped materials were investigated. It was found that substitution of up to 10% Ti by Fe does not affect the crystalline structure. Self-consistent calculations of the electronic structure predict the material to be a half-metallic ferromagnet. The Curie temperature of the Fe substituted alloy is far above room temperature (>700 K), thus making that material a serious candidate for future electronic applications, in particular, for magnetoelectronics and spintronics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.66.Fn Inorganic compounds
71.20.Nr Semiconductor compounds

Transition metal doping and clustering in Ge

A. Continenza, G. Profeta, and S. Picozzi

Appl. Phys. Lett. 89, 202510 (2006); http://dx.doi.org/10.1063/1.2388894 (3 pages) | Cited 8 times

Online Publication Date: 15 November 2006

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Ab initio calculations of clusters in Ge, up to three-impurity atoms in substitutional and/or interstitial sites, are discussed. Interstitial defects, with usually high formation energies when isolated, are stabilized thanks to the interaction with substitutional sites nearby. Mn impurities show a tendency to cluster and magnetic alignment strongly dependent on the sites; however, the occurrence of some Mn clusters is seen not to degrade magnetism, though reducing the total magnetic moment. Cr codoping leads to large formation energy and antiferromagnetic alignment. Co codoping lowers the energy cost of Mn incorporation without disrupting ferromagnetic ordering, thus representing a possible route to help Mn incorporation in Ge.
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61.72.uf Ge and Si
75.50.Pp Magnetic semiconductors
61.72.J- Point defects and defect clusters
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities

Giant coercivity nanodots and fractals in CoPt films grown on (001) SrTiO3 using pulsed laser deposition

R. K. Rakshit, S. K. Bose, R. Sharma, and R. C. Budhani

Appl. Phys. Lett. 89, 202511 (2006); http://dx.doi.org/10.1063/1.2388859 (3 pages) | Cited 7 times

Online Publication Date: 15 November 2006

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High coercivity nanoscale structures of CoPt are grown on (001) SiTiO3 with pulsed laser ablation. At low growth rate ( ≃ 0.4 Å/s), the film morphology changes from a self-similar fractal to nanodots as the deposition temperature is raised from 700 to 800 °C. While the nanodots are L10 ordered phase with out-of-plane c axis and coercivity Hc⊥ ≃ 30 kOe, the fractals have a nonzero, in-plane c-axis component of the L10 phase. The large lattice mismatch between (001) SrTiO3 and the ac/bc plane of L10 imparts tensile strain to the films whose morphological manifestations can be suppressed at high growth rates.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition

Magneto-optical study of magnetization reversal asymmetry in exchange bias

A. Tillmanns, S. Oertker, B. Beschoten, G. Güntherodt, C. Leighton, Ivan K. Schuller, and J. Nogués

Appl. Phys. Lett. 89, 202512 (2006); http://dx.doi.org/10.1063/1.2392283 (3 pages) | Cited 11 times

Online Publication Date: 16 November 2006

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The asymmetric magnetization reversal in exchange biased Fe/MnF2 involves coherent (Stoner-Wohlfarth) magnetization rotation into an intermediate, stable state perpendicular to the applied field. We provide here the experimentally tested analytical conditions for the unambiguous observation of both longitudinal and transverse magnetization components using the magneto-optical Kerr effect. This provides a fast and powerful probe of coherent magnetization reversal as well as its chirality. Surprisingly, the sign and asymmetry of the transverse magnetization component of exchange biased, low-anisotropy MnF2 and high-anisotropy FeF2 change with the angle between cooling and measurement fields.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
78.20.Ls Magneto-optical effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics

Degradation-free interfaces in MgB2/insulator/Pb Josephson tunnel junctions

Y. Cui, Ke Chen, Qi Li, X. X. Xi, and J. M. Rowell

Appl. Phys. Lett. 89, 202513 (2006); http://dx.doi.org/10.1063/1.2388891 (3 pages) | Cited 16 times

Online Publication Date: 16 November 2006

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High quality superconductor-barrier interfaces are critical for Josephson tunnel junctions. The authors show that such interfaces can be achieved in MgB2/insulator/Pb trilayer junctions using MgB2 films grown by hybrid physical-chemical vapor deposition and with barriers formed at elevated temperatures. The junctions show clear Josephson tunneling characteristics with high Jc ( ∼ 3 kA/cm2), high IcRN products ( ∼ 1.9 meV), and the expected Ic(B) pattern. The observed π gap is small (2.0 meV) and the σ gap is large (7.4 meV), in agreement with theoretical predictions and indicating that the superconducting property of MgB2 is not degraded at the MgB2-insulator interface.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
74.25.Jb Electronic structure (photoemission, etc.)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Enhanced flux pinning properties of YBa2Cu3Oy by dilute impurity doping for CuO chain

Yui Ishii, Jun-ichi Shimoyama, Yoshiaki Tazaki, Takayoshi Nakashima, Shigeru Horii, and Kohji Kishio

Appl. Phys. Lett. 89, 202514 (2006); http://dx.doi.org/10.1063/1.2387979 (3 pages) | Cited 16 times

Online Publication Date: 16 November 2006

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Effects of dilute impurity doping to the CuO chain of Y123 on the flux pinning properties were studied using single crystals and melt-solidified bulks. Cobalt-doped Y123 single crystals and iron-, cobalt- or gallium-doped Y123 melt-solidified bulks exhibited dramatically improved Jc-H characteristics accompanying huge secondary peaks in Jc-H curves. In field Jc of these samples are apparently higher than that of a low level zinc-doped bulk. These results strongly suggest that introduction of local disorders in the CuO chain by dilute impurity doping is a more promising way to improve Jc of RE123 materials than impurity doping to the CuO2 plane.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.62.Dh Effects of crystal defects, doping and substitution

Enhancement and inverse behaviors of magnetoimpedance in a magnetotunneling junction by driving frequency

W. C. Chien, C. K. Lo, L. C. Hsieh, Y. D. Yao, X. F. Han, Z. M. Zeng, T. Y. Peng, and P. Lin

Appl. Phys. Lett. 89, 202515 (2006); http://dx.doi.org/10.1063/1.2374807 (3 pages) | Cited 10 times

Online Publication Date: 17 November 2006

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The magnetoimpedance effect was employed to study magnetotunneling junction (MTJ) with the structure of Ru(5 nm)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al(1.2 nm)-oxide/CoFeB(4 nm)/Ru(5 nm). A huge change of more than ±17 000% was observed in the imaginary part of the impedance between the magnetically parallel and antiparallel states of the MTJ. The inverse behavior of the magnetoimpedance (MI) loop occurs beyond 21.1 MHz; however, the normal MI at low frequency and the inverse MI at high frequency exhibit the same magnetization reversal as checked by the Kerr effect. The reversal in MI was due to the dominance of magnetocapacitance at high frequency.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects

Perfluorocyclobutane containing polymeric gate dielectric for organic thin film transistors with high on/off ratio

Jieun Ghim, Kang-Jun Baeg, Yong-Young Noh, Seok-Ju Kang, Jang Jo, Dong-Yu Kim, Shinuk Cho, Jonathan Yuen, Kwanghee Lee, and Alan J. Heeger

Appl. Phys. Lett. 89, 202516 (2006); http://dx.doi.org/10.1063/1.2390663 (3 pages) | Cited 8 times

Online Publication Date: 17 November 2006

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A thermally cross-linkable perfluorocyclobutane (PFCB) polymer was synthesized and examined for use as the gate dielectric in organic thin film transistors (OTFTs). The PFCB polymer showed good solvent and process resistance during the photolithographic patterning of the electrodes. Bottom contact OTFTs were fabricated with poly(3-hexylthiophene)-2,5-diyl (P3HT) as the semiconductor, either spin cast or dip coated, on the PFCB gate dielectric. OTFTs fabricated with dip-coated P3HT showed a field effect mobility of 1.8×10−3 cm2/V s and a high on/off current ratio of 8.3×106 in the saturation regime, with a source-drain voltage of VD = −50 V.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
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