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13 Aug 2007

Volume 91, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 91, 071906 (2007); http://dx.doi.org/10.1063/1.2753092 (3 pages)

Cheng Zhang, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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Experimental realization of a silicon spin field-effect transistor

Biqin Huang, Douwe J. Monsma, and Ian Appelbaum

Appl. Phys. Lett. 91, 072501 (2007); http://dx.doi.org/10.1063/1.2770656 (3 pages) | Cited 18 times

Online Publication Date: 13 August 2007

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A longitudinal electric field is used to control the transit time (through an undoped silicon vertical channel) of spin-polarized electrons precessing in a perpendicular magnetic field. Since an applied voltage determines the final spin direction at the spin detector and hence the output collector current, this comprises a spin field-effect transistor. An improved hot-electron spin injector providing ≈ 115% magnetocurrent, corresponding to at least ≈ 37% electron current spin polarization after transport through 10 μm undoped single-crystal silicon, is used for maximum current modulation.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Low-temperature ordering of (001) granular FePt films by inserting ultrathin SiO2 layers

Yun-Chung Wu, Liang-Wei Wang, and Chih-Huang Lai

Appl. Phys. Lett. 91, 072502 (2007); http://dx.doi.org/10.1063/1.2770652 (3 pages) | Cited 41 times

Online Publication Date: 13 August 2007

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L10 granular FePt–SiO2 films with a (001) preferred orientation and well-separated grains of 5.14 nm were obtained by depositing atomic-scale Fe/Pt/SiO2 multilayers (MLs) on glass substrates and subsequently annealing MLs at a temperature of 350 °C. Large out-of-plane coercivity of 7700 Oe and a high ordering factor of 0.83 were achieved. Alternate atomic-scale depositions promoted the formation of (001) textures. Furthermore, because of the low surface energy of SiO2 layers, SiO2 tended to diffuse into grain boundaries of FePt during annealing, which may accelerate diffusion of Fe and Pt atoms, resulting in the low-temperature ordering.
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75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies
68.35.Fx Diffusion; interface formation

Synthesis and magnetic properties of (Nd1−xSmx)5Fe17 (x = 0–1) phase

Tetsuji Saito

Appl. Phys. Lett. 91, 072503 (2007); http://dx.doi.org/10.1063/1.2770771 (3 pages) | Cited 2 times

Online Publication Date: 13 August 2007

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An investigation of the synthesis of the (Nd1−xSmx)5Fe17 (x = 0–1) phase and its magnetic properties is presented. It was found that the (Nd1−xSmx)5Fe17 (x = 0–1) phase can be produced by annealing of the amorphous melt-spun ribbon, regardless of the Sm content of the phase. The Curie temperature and coercivity of the (Nd1−xSmx)5Fe17 (x = 0–1) phase increased with its Sm content.
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81.05.Bx Metals, semimetals, and alloys
75.50.Ww Permanent magnets
75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments

Charge order suppression and weak ferromagnetism in La1/3Sr2/3FeO3 nanoparticles

F. Gao, P. L. Li, Y. Y. Weng, S. Dong, L. F. Wang, L. Y. Lv, K. F. Wang, J.-M. Liu, and Z. F. Ren

Appl. Phys. Lett. 91, 072504 (2007); http://dx.doi.org/10.1063/1.2768895 (3 pages) | Cited 13 times

Online Publication Date: 14 August 2007

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Perovskite-type polycrystalline La1/3Sr2/3FeO3 particles with different sizes (80–2000 nm) were prepared using a simple sol-gel technique. In samples of nanoparticles with a diameter of less than 300 nm, weak ferromagnetism was observed at room temperature, which was attributed to the lattice distortion. The magnetic and specific heat measurements suggest that the charge ordering state was largely suppressed due to the lowering of the particle size, but the charge ordering temperature remained unaffected.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Nuclear magnetic resonance in the earth’s magnetic field using a nitrogen-cooled superconducting quantum interference device

Longqing Qiu, Yi Zhang, Hans-Joachim Krause, Alex I. Braginski, Martin Burghoff, and Lutz Trahms

Appl. Phys. Lett. 91, 072505 (2007); http://dx.doi.org/10.1063/1.2771060 (3 pages) | Cited 23 times

Online Publication Date: 14 August 2007

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The authors recorded nuclear magnetic resonance (NMR) spectra of water, benzene, fluorobenzene, and 2,2,2-trifluoroethanol in the earth’s magnetic field (EMF) using a nitrogen-cooled superconducting quantum interference device (SQUID). In trifluoroethanol, the broadband detection characteristics of the SQUID with a noise floor of about 70 fT/√Hz enabled authors to simultaneously observe fluorine and proton spectra at 1940 and 2060 Hz Larmor frequency, reflecting their heteronuclear J coupling in the high-field limit without showing a measurable chemical shift. To reduce the noise in EMF-NMR, the authors suggest the use of frequency-adjusted averaging, which compensates line broadening due to EMF fluctuations.
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76.60.-k Nuclear magnetic resonance and relaxation
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Nonvolatile memory effect of capacitance in polycrystalline spinel vanadate

H. Takei, T. Suzuki, and T. Katsufuji

Appl. Phys. Lett. 91, 072506 (2007); http://dx.doi.org/10.1063/1.2771041 (3 pages) | Cited 5 times

Online Publication Date: 14 August 2007

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The authors found that capacitance of polycrystalline spinel FeV2O4 exhibits a magnetic-field dependence with hysteresis and takes two values at zero field depending on the direction of a small magnetic field ( ∼ 1000 G) applied prior to measurement. This behavior can be potentially used as a nonvolatile memory device in which the data are stored as a difference of capacitance through the change of magnetic-field directions.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.-y Studies of specific magnetic materials

X-ray magnetic circular dichroism characterization of GaN/Ga1−xMnxN digital ferromagnetic heterostructure

J. I. Hwang, M. Kobayashi, G. S. Song, A. Fujimori, A. Tanaka, Z. S. Yang, H. J. Lin, D. J. Huang, C. T. Chen, H. C. Jeon, and T. W. Kang

Appl. Phys. Lett. 91, 072507 (2007); http://dx.doi.org/10.1063/1.2769944 (3 pages) | Cited 6 times

Online Publication Date: 15 August 2007

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The authors have investigated the magnetic properties of a GaN/Ga1−xMnxN (x = 0.1) digital ferromagnetic heterostructure (DFH) showing ferromagnetic behavior using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The Mn L2,3-edge XAS spectra were similar to those of Ga1−xMnxN random alloy thin films, indicating a substitutional doping of high concentration Mn into GaN. From the XMCD measurements, it was revealed that paramagnetic and ferromagnetic Mn atoms coexisted in the Ga1−xMnxN digital layers. Subtle differences were also found from the XMCD spectra between the electronic states of the ferromagnetic and paramagnetic Mn2+ ions. The ferromagnetic moment per Mn atom estimated from XMCD agreed well with that estimated from superconducting quantum interference device measurements, indicating that the ferromagnetic behavior of the GaN/Ga1−xMnxN DFH sample arises only from substitutional Mn2+ ions in the Ga1−xMnxN digital layers and not from ferromagnetic precipitates.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Pp Magnetic semiconductors

Dipole-induced magnetic anisotropy in γ-Fe2O3(001) epitaxial films

H. Yanagihara, J. Hagiwara, M. Nakazumi, Eiji Kita, and T. Furubayashi

Appl. Phys. Lett. 91, 072508 (2007); http://dx.doi.org/10.1063/1.2771062 (3 pages) | Cited 6 times

Online Publication Date: 15 August 2007

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The authors investigated the magnetic anisotropy of epitaxial films of γ-Fe2O3(001) composed entirely of Fe3+. The cubic anisotropy term (K1) was negligibly small (K1 ≈ −2.7×104 erg/cm3), as expected for L ≈ 0 systems; however, substantially large uniaxial anisotropy energy (Ku ≈ 6.1×105 erg/cm3) was found as the thickness reached the bulk limit. A detailed characterization of both the in-plane and out-of-plane lattice parameters revealed that the c/a ratio of the unit cell was intrinsically elongated due to its vacancy-ordered supercell. This unexpectedly large Ku is reasonably explained by simple dipole sums if the authors take into account the slightly stretched unit cell (c′/a = 1.03) in the growth direction even without the spin-orbit interaction.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology

Controlled interface profile in Sm–Co/Fe exchange-spring magnets

Y. Choi, J. S. Jiang, J. E. Pearson, S. D. Bader, J. J. Kavich, J. W. Freeland, and J. P. Liu

Appl. Phys. Lett. 91, 072509 (2007); http://dx.doi.org/10.1063/1.2769755 (3 pages) | Cited 21 times

Online Publication Date: 16 August 2007

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In exchange-spring magnets with temperature-induced interfacial intermixing, differences in the extent of diffusion of constituent elements typically lead to local compositional changes. The authors demonstrate that adding an artificially created intermixed layer in Sm–Co/Fe exchange-spring permanent magnets enhances the exchange coupling effectiveness without modifying the local composition of the Sm–Co layer. Element- and depth-resolved magnetization measurements verify that the diffusion extent of Sm and Co is similar across the interface.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
68.35.Fx Diffusion; interface formation
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Exchange bias behavior in Ni–Mn–Sb Heusler alloys

Mahmud Khan, Igor Dubenko, Shane Stadler, and Naushad Ali

Appl. Phys. Lett. 91, 072510 (2007); http://dx.doi.org/10.1063/1.2772233 (3 pages) | Cited 59 times

Online Publication Date: 16 August 2007

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The authors report the observation of exchange bias in bulk polycrystalline Ni50Mn25+xSb25−x Heusler alloys. Shifts in hysteresis loops of up to 248 Oe were observed in the 5 T field cooled samples. The observed exchange bias behavior in Ni50Mn25+xSb25−x is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. Such behavior is an addition to the multifunctional properties of the Ni50Mn25+xSb25−x Heusler alloy system.
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75.30.Et Exchange and superexchange interactions
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Role of point defects in room-temperature ferromagnetism of Cr-doped ZnO

Hui Liu, Xiao Zhang, Luyan Li, Y. X. Wang, K. H. Gao, Z. Q. Li, R. K. Zheng, S. P. Ringer, Bei Zhang, and X. X. Zhang

Appl. Phys. Lett. 91, 072511 (2007); http://dx.doi.org/10.1063/1.2772176 (3 pages) | Cited 54 times

Online Publication Date: 17 August 2007

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Polycrystalline CrxZn1−xO films and powders are prepared by cosputtering and sol-gel method, respectively. While room-temperature ferromagnetism is found in as-deposited films, the powders exhibit paramagnetism. Comparison of the structural and magnetic properties of the as-deposited, annealed, and powdered samples indicates that the interstitial zinc, together with Cr doping, plays an important role in the ferromagnetic origin of Cr:ZnO. The ferromagnetism in films can be described by bound magnetic polaron models with respect to defect-bound carriers.
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81.05.Dz II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.-m Intrinsic properties of magnetically ordered materials

Linear and nonlinear electrodynamic responses of bulk CaC6 in the microwave regime

A. Andreone, G. Cifariello, E. Di Gennaro, G. Lamura, N. Emery, C. Hérold, J. F. Marêché, and P. Lagrange

Appl. Phys. Lett. 91, 072512 (2007); http://dx.doi.org/10.1063/1.2769763 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2007

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The linear and nonlinear responses to a microwave electromagnetic field of two c-axis oriented polycrystalline samples of the recently discovered superconductor CaC6 (TC ≈ 11.5 K) is studied in the superconducting state down to 2 K. The surface resistance RS and the third order intermodulation distortion, arising from a two-tone excitation, have been measured as a function of temperature and microwave circulating power. Experiments are carried out using a dielectrically loaded copper cavity operating at 7 GHz in a “hot finger” configuration. The results confirm recent experimental findings that CaC6 behaves as a weakly coupled, fully gapped, superconductor.
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74.25.N- Response to electromagnetic fields
74.25.F- Transport properties

Amplification of spin-current polarization

D. Saha, M. Holub, and P. Bhattacharya

Appl. Phys. Lett. 91, 072513 (2007); http://dx.doi.org/10.1063/1.2772660 (3 pages) | Cited 16 times

Online Publication Date: 17 August 2007

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A ferromagnet/semiconductor based electrically controlled spin-current amplifier using a dual-drain nonlocal lateral spin valve is demonstrated. The spin polarization injected by the source into the channel is amplified at the second drain contact. An amplified current spin polarization of 100% is measured. The controlled variation of amplifier gain with bias is also demonstrated. The observations are explained in the framework of the spin drift-diffusion model.
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72.25.Dc Spin polarized transport in semiconductors
72.25.Hg Electrical injection of spin polarized carriers
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Effect of annealing on the magnetic properties of Gd focused ion beam implanted GaN

M. A. Khaderbad, S. Dhar, L. Pérez, K. H. Ploog, A. Melnikov, and A. D. Wieck

Appl. Phys. Lett. 91, 072514 (2007); http://dx.doi.org/10.1063/1.2770762 (3 pages) | Cited 20 times

Online Publication Date: 17 August 2007

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The authors have studied the effect of annealing on the magnetic and the structural properties of Gd focused ion beam implanted GaN samples. Molecular beam epitaxy grown GaN layers, which were implanted with 300 keV Gd3+ ions at room temperature at doses 2.4×1011 and 1.0×1015 cm−2, are rapid thermally annealed in flowing N2 gas up to 900 °C for 30 s. X-ray diffraction results indicate the presence of Ga and N interstitials in the implanted layers. Their densities are also found to reduce upon annealing. At the same time, magnetic measurements on these samples clearly show a reduction in the saturation magnetization as a result of the annealing for the lowest Gd incorporated sample, while in the highest Gd incorporated sample it does not change. These findings suggest that Gd might be inducing magnetic moment in Ga and/or N interstitials in giving rise to an effective colossal magnetic moment of Gd and the associated ferromagnetism observed in Gd:GaN.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
75.50.Pp Magnetic semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
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