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5 Jan 2009

Volume 94, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 94, 013102 (2009); http://dx.doi.org/10.1063/1.3062938 (3 pages)

Hao-Chih Yuan, Jonghyun Shin, Guoxuan Qin, Lei Sun, Pallab Bhattacharya, Max G. Lagally, George K. Celler, and Zhenqiang Ma
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Disorder effects in half-metallic Sr2FeMoO6 single crystals

Raghava P. Panguluri, Sheng Xu, Yutaka Moritomo, I. V. Solovyev, and B. Nadgorny

Appl. Phys. Lett. 94, 012501 (2009); http://dx.doi.org/10.1063/1.3058441 (3 pages) | Cited 8 times

Online Publication Date: 5 January 2009

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Double perovskites such as Sr2FeMoO6 (SFMO) have been predicted to be half-metallic (100% spin polarized). However, this conclusion is reached under the assumption that SFMO has a perfect crystalline structure. We measure the values of spin polarization P for SFMO single crystals with 11%, 15%, and 16% of B-site disorder using the point contact Andreev reflection technique. The highest spin polarization of P ≈ 70% was determined. Using local spin density approximation, we compute P ≈ 53% for the degree of B-site disorder of 12.5% in good agreement with the experimental results. While our results show that imperfect SFMO is not a half-metal, the observed correlation between the degree of antisite disorder, the magnetic properties, and the values of spin polarization implies that a perfectly ordered SFMO crystal might be half-metallic.
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72.25.-b Spin polarized transport
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.80.Sk Insulators
75.30.Cr Saturation moments and magnetic susceptibilities

Reducing the critical current for spin-transfer switching of perpendicularly magnetized nanomagnets

S. Mangin, Y. Henry, D. Ravelosona, J. A. Katine, and Eric E. Fullerton

Appl. Phys. Lett. 94, 012502 (2009); http://dx.doi.org/10.1063/1.3058680 (3 pages) | Cited 54 times

Online Publication Date: 6 January 2009

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We describe nanopillar spin valves with perpendicular anisotropy designed to reduce the critical current needed for spin transfer magnetization reversal while maintaining thermal stability. By adjusting the perpendicular anisotropy and volume of the free element consisting of a [Co/Ni] multilayer, we observe that the critical current scales with the height of the anisotropy energy barrier and we achieve critical currents as low as 120 μA in quasistatic room-temperature measurements of a 45 nm diameter device. The field-current phase diagram of such a device is presented.
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75.75.-c Magnetic properties of nanostructures
72.25.Ba Spin polarized transport in metals
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Jk Magnetization reversal mechanisms

Superconductivity in S-substituted FeTe

Yoshikazu Mizuguchi, Fumiaki Tomioka, Shunsuke Tsuda, Takahide Yamaguchi, and Yoshihiko Takano

Appl. Phys. Lett. 94, 012503 (2009); http://dx.doi.org/10.1063/1.3058720 (3 pages) | Cited 80 times

Online Publication Date: 6 January 2009

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We synthesized a superconducting system of FeTe1−xSx with a PbO-type structure. It has the simplest crystal structure among iron-based superconductors. The superconducting transition temperature is about 10 K when x is 0.2. The upper critical field Bc2(0) was estimated to be ~70 T. The coherent length was calculated to be ~2.2 nm. Since FeTe1−xSx is composed of nontoxic elements, this material is a candidate for applications that will further advance research on iron-based superconductors.
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74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
61.66.Fn Inorganic compounds

Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb/Si

Da-Li Sun, De-Yong Wang, Hai-Feng Du, Wei Ning, Jian-Hua Gao, Ya-Peng Fang, Xiang-Qun Zhang, Young Sun, Zhao-Hua Cheng, and Jian Shen

Appl. Phys. Lett. 94, 012504 (2009); http://dx.doi.org/10.1063/1.3054340 (3 pages) | Cited 5 times

Online Publication Date: 6 January 2009

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We fabricated quasi-one-dimensional Fe chains on a 4° miscut Si (111) substrate with a Pb film as a buffer layer. The magnetic properties and morphology of Fe chains were investigated by means of scanning tunneling microscope (STM) and surface magneto-optical Kerr effect (SMOKE). STM images show that Fe chains are formed by Fe random islands along the steps of the Pb film due to step decoration. SMOKE data indicate that the Fe chains exhibit in-plane uniaxial magnetic anisotropy along the step direction. The effective in-plane uniaxial anisotropy constant at room temperature was determined by means of electron spin resonance.
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75.30.Gw Magnetic anisotropy
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.20.Ls Magneto-optical effects
78.68.+m Optical properties of surfaces
75.75.-c Magnetic properties of nanostructures
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Dispersion in magnetostatic CoTaZr spin waveguides

A. Kozhanov, D. Ouellette, Z. Griffith, M. Rodwell, A. P. Jacob, D. W. Lee, S. X. Wang, and S. J. Allen

Appl. Phys. Lett. 94, 012505 (2009); http://dx.doi.org/10.1063/1.3063124 (3 pages) | Cited 11 times

Online Publication Date: 7 January 2009

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Magnetostatic spin wave dispersion and loss are measured in micron scale spin waveguides in ferromagnetic metallic CoTaZr. Results are in good agreement with model calculations of spin wave dispersion and up to three different modes are identified. Attenuation lengths of the order of 3 μm are several orders of magnitude shorter than that predicted from eddy currents in these thin wires.
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75.50.Cc Other ferromagnetic metals and alloys
75.30.Ds Spin waves
75.60.-d Domain effects, magnetization curves, and hysteresis

Broadband ferromagnetic resonance linewidth measurement of magnetic tunnel junction multilayers

J. F. Sierra, F. G. Aliev, R. Heindl, S. E. Russek, and W. H. Rippard

Appl. Phys. Lett. 94, 012506 (2009); http://dx.doi.org/10.1063/1.3054642 (3 pages) | Cited 3 times

Online Publication Date: 7 January 2009

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The broadband ferromagnetic resonance (FMR) linewidth of the free layer of magnetic tunnel junctions is used as a simple diagnostic of the quality of the magnetic structure. The FMR linewidth increases near the field regions of free layer reversal and pinned layer reversal, and this increase correlates with an increase in magnetic hysteresis in unpatterned films, low-frequency noise in patterned devices, and previous observations of magnetic domain ripple by use of Lorentz microscopy. Postannealing changes the free layer FMR linewidth, indicating that considerable magnetic disorder, originating in the exchange-biased pinned layer, is transferred to the free layer.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Enhanced magnetoresistance in self-assembled monolayer of oleic acid molecules on Fe3O4 nanoparticles

S. Wang, F. J. Yue, D. Wu, F. M. Zhang, W. Zhong, and Y. W. Du

Appl. Phys. Lett. 94, 012507 (2009); http://dx.doi.org/10.1063/1.3059571 (3 pages) | Cited 12 times

Online Publication Date: 8 January 2009

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Spin transport through molecules is investigated using self-assembled monolayers of oleic acid molecules on half metallic Fe3O4 nanoparticles. Fourier transform infrared spectroscopy measurements indicate that 1 ML (monolayer) molecules chemically bond to the Fe3O4 nanoparticles and the physically absorbed molecules do not exist in the samples. The magnetoresistance (MR) of cold-pressed, molecule fully covered nanoparticles is up to 7.3% at room temperature and 17.5% at 115 K under a field of 5.8 kOe. The MR ratio is more than two times larger than that of pure Fe3O4 nanoparticles. This enhanced MR is likely arising from weak spin scattering while carriers hop through the oleic acid molecules. These results show that small molecules are promising for development of future spin-based molecular electronics.
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72.20.My Galvanomagnetic and other magnetotransport effects
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
61.50.Lt Crystal binding; cohesive energy
72.25.Rb Spin relaxation and scattering
78.30.-j Infrared and Raman spectra
68.43.Fg Adsorbate structure (binding sites, geometry)

Strong influence of a magnetic layer on the critical current of Nb bridge in finite magnetic fields due to surface barrier effect

D. Y. Vodolazov, B. A. Gribkov, A. Yu. Klimov, V. V. Rogov, and S. N. Vdovichev

Appl. Phys. Lett. 94, 012508 (2009); http://dx.doi.org/10.1063/1.3030983 (3 pages) | Cited 6 times

Online Publication Date: 9 January 2009

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We measured the critical current of the bilayer Nb/Co in the applied magnetic field. When the magnetic field was tilted to the axis which was perpendicular to the plane of the bilayer we observed a large difference in critical currents flowing in opposite directions. We found that the largest critical current of the bilayer exceeded the critical current of the superconductor without Co layer in a wide range of the tilted magnetic fields. The theory which takes into account the surface barrier effect for vortex entry and magnetic field of the magnetic layer gave a quantitative explanation of our experimental results.
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74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.70.Ak Magnetic properties of monolayers and thin films
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Spin-lattice coupling in multiferroic Pb(Fe1/2Nb1/2)O3 thin films

Wei Peng, Nathalie Lemée, Michael Karkut, Brahim Dkhil, Vladimir V. Shvartsman, Pavel Borisov, Wolfgang Kleemann, Janez Holc, Marija Kosec, and Robert Blinc

Appl. Phys. Lett. 94, 012509 (2009); http://dx.doi.org/10.1063/1.3067872 (3 pages) | Cited 12 times

Online Publication Date: 9 January 2009

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We made magnetization and x-ray diffraction measurements on an epitaxial Pb(Fe1/2Nb1/2)O3 200 nm film. From the temperature dependence of the out-of-plane lattice parameter, we can assign a Burns’ temperature at Td ∼ 640 K, a temperature at T∗ ∼ 510 K (related to the appearance of static polar nanoregions), and an anomaly occurring at 200 K. The latter is precisely the Néel temperature TN determined from magnetization and points to spin-lattice coupling at TN ∼ 200 K. We also observe “weak ferromagnetism” up to 300 K and propose superantiferromagnetic clusters as a plausible scenario to explain this hysteresis above TN.
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77.55.-g Dielectric thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Ferromagnetism in Ni-doped ZnO films: Extrinsic or intrinsic?

Michael Snure, Dhananjay Kumar, and Ashutosh Tiwari

Appl. Phys. Lett. 94, 012510 (2009); http://dx.doi.org/10.1063/1.3067998 (3 pages) | Cited 21 times

Online Publication Date: 9 January 2009

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Here we report a detailed study aimed on understanding the origin of ferromagnetism in Ni-doped ZnO films. A pulsed laser deposition technique was used to deposit Ni-doped (5 at. %) ZnO films on sapphire (0001) substrates under different oxygen pressures ranging from 10−6 to 0.1 Torr. Films were characterized using numerous characterization techniques including x-ray diffraction, x-ray photospectroscopy, energy dispersive x-ray spectroscopy, optical absorption spectroscopy, and electrical transport, magnetotransport, and magnetization measurements. A detailed structure-property correlation and analysis of our results revealed that the ferromagnetism in ZnO:Ni films is not an inherent property of the material but results due to a strong tendency of Ni to precipitate out in the ZnO matrix.
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75.50.Pp Magnetic semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
75.70.Ak Magnetic properties of monolayers and thin films

Enhancement of spin-asymmetry by L21-ordering in Co2MnSi/Cr/Co2MnSi current-perpendicular-to-plane magnetoresistance devices

Y. Sakuraba, T. Iwase, K. Saito, S. Mitani, and K. Takanashi

Appl. Phys. Lett. 94, 012511 (2009); http://dx.doi.org/10.1063/1.3068492 (3 pages) | Cited 23 times

Online Publication Date: 9 January 2009

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Co2MnSi/Cr/Co2MnSi (001)-fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices were fabricated via an UHV magnetron sputtering system. The relationship between the degree of chemical ordering in Co2MnSi (CMS) and the CPP-GMR characteristics was investigated systematically against the annealing temperature of the devices. X-ray diffraction profiles and reflection high-energy electron diffraction images indicated that annealing improved L21-ordering. The MR ratio also increased upon annealing and the maximum MR ratio of 5.2% and ΔRA of 6.5 mΩ μm2 were achieved by annealing at 400 °C. These results indicate that promoting the degree of L21-ordering in CMS enhances the bulk and/or interface spin-asymmetry coefficients.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Pt/Co/oxide and oxide/Co/Pt electrodes for perpendicular magnetic tunnel junctions

L. E. Nistor, B. Rodmacq, S. Auffret, and B. Dieny

Appl. Phys. Lett. 94, 012512 (2009); http://dx.doi.org/10.1063/1.3064162 (3 pages) | Cited 33 times

Online Publication Date: 9 January 2009

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This letter presents a study of perpendicular magnetic anisotropy in oxide/Co/Pt structures, which could constitute the upper magnetic electrode of magnetic tunnel junctions. The growth of cobalt layers on SiO2 substrates shows that all 0.6 nm thick Co films are superparamagnetic, whereas perpendicular magnetic anisotropy is obtained for 1.5 nm films after annealing. Co layers grown on various Al and Mg oxides prepared by sputtering also exhibit perpendicular magnetic anisotropy after annealing. Combined with inverse Pt/Co(CoFeB)/oxide stackings, these structures allow preparing tunnel junctions with thicker magnetic electrodes and much better thermal stability than those based on standard Pt/Co multilayers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
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