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3 Apr 2006

Volume 88, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 88, 143508 (2006); http://dx.doi.org/10.1063/1.2191448 (3 pages)

R. Chan, M. Feng, N. Holonyak, A. James, and G. Walter
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Vortex-flow electromagnetic emission in stacked intrinsic Josephson junctions

Myung-Ho Bae and Hu-Jong Lee

Appl. Phys. Lett. 88, 142501 (2006); http://dx.doi.org/10.1063/1.2191415 (3 pages) | Cited 6 times

Online Publication Date: 3 April 2006

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We confirmed the existence of the collective transverse plasma modes excited by the motion of the Josephson vortex lattice in stacked intrinsic Josephson junctions of Bi2Sr2CaCu2O8+x by observing the multiple subbranches in the Josephson-vortex-flow current-voltage characteristics. We also observed the symptom of the microwave emission from the resonance between the Josephson vortex lattice and the collective transverse plasma modes, which provides the possibility of developing Josephson-vortex-flow electromagnetic oscillators.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
74.25.F- Transport properties

Ferromagnetism in 200-MeV Ag+15-ion-irradiated Co-implanted ZnO thin films

Basavaraj Angadi, Y. S. Jung, Won-Kook Choi, Ravi Kumar, K. Jeong, S. W. Shin, J. H. Lee, J. H. Song, M. Wasi Khan, and J. P. Srivastava

Appl. Phys. Lett. 88, 142502 (2006); http://dx.doi.org/10.1063/1.2192577 (3 pages) | Cited 20 times

Online Publication Date: 4 April 2006

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Structural, electrical resistivity, and magnetization properties of 200-MeV Ag+15-ion-irradiated Co-implanted ZnO thin films are presented. The structural studies show the presence of Co clusters whose size is found to increase with increase of Co implantation. The implanted films were irradiated with 200-MeV Ag+15 ions to fluence of 1×1012 ions/cm2. The Co clusters on irradiation dissolve in the ZnO matrix. The electrical resistivity of the irradiated samples is lowered to half. The magnetization hysteresis measurements show ferromagnetic behavior at 300 K, and the coercive field increases with the Co implantation. The ferromagnetism at room temperature is confirmed by magnetic force microscopy measurements. The results are explained on the basis of the close interplay between the electrical and the magnetic properties.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.82.Fk Semiconductors

Multiferroic BiFeO3 thin films prepared via a simple sol-gel method

Yao Wang, Qing-hui Jiang, Hong-cai He, and Ce-Wen Nan

Appl. Phys. Lett. 88, 142503 (2006); http://dx.doi.org/10.1063/1.2191947 (3 pages) | Cited 53 times

Online Publication Date: 4 April 2006

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Single-phase multiferroic BiFeO3 thin films were grown on (111) Pt/Ti/SiO2/Si substrates via a simple sol-gel spin-coating technique, as evidenced by x-ray diffraction. The thickness of the films can be controlled by the number of layers spin coated. Scanning electron microscope confirmed good surface and cross-section morphology of the films. Obvious multiferroic behavior with small saturation polarization but high saturation magnetization was observed in the films. X-ray photoelectron spectroscopy was used to examine the combination state of Fe 2p electron in the BiFeO3 films.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Magnetoelectric effect in laminate composite of magnets/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal

Yanmin Jia, Xiangyong Zhao, Haosu Luo, Siu Wing Or, and Helen Lai Wa Chan

Appl. Phys. Lett. 88, 142504 (2006); http://dx.doi.org/10.1063/1.2191948 (3 pages) | Cited 9 times

Online Publication Date: 4 April 2006

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A magnetoelectric (ME) laminate composite was fabricated by sandwiching one 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN-PT) piezoelectric single crystal layer between two NdFeB magnet layers along the thickness direction. The high ME effect was obtained by the product of the magnetic attractive-repellent effect in the magnet layers and the piezoelectric effect in the piezoelectric layer. The magnetoelectric voltage coefficient of the composite was measured to be ∼ 12.5 mV/cm Oe with a flat frequency response in the range of 0.1–20 kHz. The induced ME voltage showed an excellent linear relationship to the applied ac magnetic field with field amplitude varying from 10−3 to 10 Oe. Other advantages included low heat generation, no bias magnetic field required, and high scale-down capability. These made the composite to be a promising ME material for realizing high-performance, small-size, and low-cost magnetic sensors.
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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

Search for ferromagnetism in undoped and cobalt-doped HfO2−δ

M. S. Ramachandra Rao, Darshan C. Kundaliya, S. B. Ogale, L. F. Fu, S. J. Welz, N. D. Browning, V. Zaitsev, B. Varughese, C. A. Cardoso, A. Curtin, S. Dhar, S. R. Shinde, T. Venkatesan, S. E. Lofland, and S. A. Schwarz

Appl. Phys. Lett. 88, 142505 (2006); http://dx.doi.org/10.1063/1.2190909 (3 pages) | Cited 22 times

Online Publication Date: 5 April 2006

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We report on the search for ferromagnetism in undoped and cobalt-doped high-k dielectric HfO2 films. Over a broad range of growth conditions, we do not observe ferromagnetism in undoped HfO2 films. On the other hand, we do observe room temperature ferromagnetism in dilutely Co-doped HfO2 films, but the origin of the same appears extrinsic (a Co rich surface layer) at least for the regime of growth conditions explored.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy

Enhancement of the upper critical field of Nb3Sn utilizing disorder introduced by ball milling the elements

L. D. Cooley, Y. F. Hu, and A. R. Moodenbaugh

Appl. Phys. Lett. 88, 142506 (2006); http://dx.doi.org/10.1063/1.2193047 (3 pages) | Cited 6 times

Online Publication Date: 5 April 2006

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Nb3Sn was prepared by milling Nb and Sn powder mixtures followed by limited reactions to restrict disorder recovery. Although disorder reduced the superconducting critical temperature Tc, the concomitant electron scattering increased the upper critical field μ0Hc2 to as high as 35 T at 0 K, as determined by the Werthamer-Helfand-Hohenberg equation. Hc2 was higher for longer milling times and lower annealing temperatures. Substitution of 2% Ti for Nb did not appreciably enhance Hc2, suggesting that alloying mitigates the benefits of disorder. Since alloyed Nb3Sn wires have μ0Hc2(0) ≈ 29 T, wires based on heavily milled powders could extend the field range for applications if they can be made with high current density.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Op Mixed states, critical fields, and surface sheaths

Current-assisted magnetization switching in a mesoscopic NiFe ring with nanoconstrictions of a wire

Zhengqi Lu, Yun Zhou, Yuqing Du, Roy Moate, David Wilton, Genhua Pan, Yifang Chen, and Zheng Cui

Appl. Phys. Lett. 88, 142507 (2006); http://dx.doi.org/10.1063/1.2195007 (3 pages) | Cited 8 times

Online Publication Date: 6 April 2006

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A mesoscopic NiFe ring with nanoconstrictions of a wire was fabricated by electron beam lithography and lift-off techniques. Magnetic switching and reversal process have been measured by magnetoresistance as a function of the applied current. It is shown that the applied current has an effect on the switching fields and finally affects the reversal process. The decrease or increase in the switching field from the vortex state to the onion state depends on the electron flow with respect to the direction of domain propagation. The spin in the ring switches from an onion state to the opposite onion state in the low applied current via the double switching process. However, the spin in the ring switches directly from an onion state to the opposite due to the spin torque effect when the applied current is higher than the critical current density (of 107 A/cm2).
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75.60.Jk Magnetization reversal mechanisms
72.15.Gd Galvanomagnetic and other magnetotransport effects

Electric-field-induced resistance switching universally observed in transition-metal-oxide thin films

M. Hamaguchi, K. Aoyama, S. Asanuma, Y. Uesu, and T. Katsufuji

Appl. Phys. Lett. 88, 142508 (2006); http://dx.doi.org/10.1063/1.2193328 (3 pages) | Cited 34 times

Online Publication Date: 6 April 2006

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We show that polarity-dependent, nonvolatile resistance switching by electric field occurs in the thin film of various transition-metal oxides in almost the same manner. This result indicates that, contrary to the general acceptance, perovskite manganite is by no means a special compound for this phenomenon. It is also suggested that the resistance switching is not dominated by a detailed electronic structure of each sample, but dominated by a more general origin, e.g., crystalline defect.
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73.61.Ng Insulators
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Room-temperature ferromagnetism in zinc-blende and deformed CrAs thin films

J. F. Bi, J. H. Zhao, J. J. Deng, Y. H. Zheng, S. S. Li, X. G. Wu, and Q. J. Jia

Appl. Phys. Lett. 88, 142509 (2006); http://dx.doi.org/10.1063/1.2193430 (3 pages) | Cited 16 times

Online Publication Date: 6 April 2006

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We try to clarify the controversy about the origin of room-temperature ferromagnetism in a CrAs compound. Two kinds of CrAs thin films were grown on GaAs by molecular-beam epitaxy. Structural analyses confirm that the as-grown CrAs film is a pure zinc-blende phase. Magnetic measurements suggest that room-temperature ferromagnetism exists in zinc-blende CrAs. In contrast, the CrAs film turns into a mixture of zinc-blende and deformed CrAs after annealing. A ferromagnetic signal measured at room temperature demonstrates that zinc-blende CrAs remains room-temperature ferromagnetism even when it is partly deformed into a non-zinc-blende phase.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films

Intrinsic nonlinearity probed by intermodulation distortion microwave measurements on high quality MgB2 thin films

G. Cifariello, M. Aurino, E. Di Gennaro, G. Lamura, A. Andreone, P. Orgiani, X. X. Xi, and J.-C. Villégier

Appl. Phys. Lett. 88, 142510 (2006); http://dx.doi.org/10.1063/1.2193053 (3 pages) | Cited 5 times

Online Publication Date: 6 April 2006

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The two-tone intermodulation distortion arising in MgB2 thin films synthesized by hybrid physical-chemical vapor deposition is studied in order to probe the influence of the two bands on the nonlinear response of this superconductor. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7 GHz. Microwave data on samples having critical temperatures above 41 K, very low resistivity values, and residual resistivity ratio larger than 10 are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, the signal arising from distortion versus temperature shows the intrinsic s-wave behavior expected for this compound. Data are compared with measurements performed on Nb and YBa2Cu3O7−δ thin films using the same technique.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.N- Response to electromagnetic fields
74.25.F- Transport properties
74.10.+v Occurrence, potential candidates
74.62.Yb Other effects
74.78.-w Superconducting films and low-dimensional structures

Ferromagnetism in Co doped CeO2: Observation of a giant magnetic moment with a high Curie temperature

Ashutosh Tiwari, V. M. Bhosle, S. Ramachandran, N. Sudhakar, J. Narayan, S. Budak, and A. Gupta

Appl. Phys. Lett. 88, 142511 (2006); http://dx.doi.org/10.1063/1.2193431 (3 pages) | Cited 71 times

Online Publication Date: 7 April 2006

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We report room temperature ferromagnetism in single crystal Ce1−xCoxO2−δ (x ⩽ 0.05) films deposited on a LaAlO3(001) substrate. Films were grown by a pulsed laser deposition technique and were thoroughly characterized using x-ray diffraction, high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy and scanning transmission electron microscopy-Z contrast, x-ray photoelectron spectroscopy, optical transmission spectroscopy, and magnetic measurements. These films are transparent in the visible regime and exhibit a very high Curie temperature ∼ 740–875 K with a giant magnetic moment. Our results indicate that the ferromagnetic property is intrinsic to the CeO2 system and is not a result of any secondary magnetic phase or cluster formation.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.20.Uv Electron energy loss spectroscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Comparison of free surface polarization of NiMnSb and Co2MnSi

Y. Miyoshi, Y. Bugoslavsky, M. H. Syed, T. Robinson, L. F. Cohen, L. J. Singh, Z. H. Barber, C. E. A. Grigorescu, S. Gardelis, J. Giapintzakis, and W. Van Roy

Appl. Phys. Lett. 88, 142512 (2006); http://dx.doi.org/10.1063/1.2193787 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2006

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We present a systematic study of the polarization of the transport current from a variety of NiMnSb and Co2MnSi thin films and bulk material using point contact Andreev reflection spectroscopy. The simple analysis suggests that the free surface polarization of NiMnSb is within error 10% lower than that of Co2MnSi. In either material the measured polarization is rather insensitive to key physical and material properties. We use a two channel model to rule out the influence that stray magnetic field from the ferromagnet might have on the measurements presented.
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73.61.At Metal and metallic alloys
72.25.Ba Spin polarized transport in metals

Identification of unidirectional anisotropy in exchange-biased MnO/GaMnAs bilayers using ferromagnetic resonance

K. Dziatkowski, Z. Ge, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 88, 142513 (2006); http://dx.doi.org/10.1063/1.2190767 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2006

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We report ferromagnetic resonance (FMR) studies of epitaxial MnO/GaMnAs bilayers. The FMR data have revealed a distinct unidirectional anisotropy about the [1math0] axis, which we attribute to exchange biasing of ferromagnetic GaMnAs by the adjacent antiferromagnetic MnO layer. The observed unidirectional anisotropy is surprisingly robust with respect to temperature and changing magnetic field.
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75.50.Pp Magnetic semiconductors
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
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