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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Planar S-(S/F)-S Josephson junctions induced by the inverse proximity effect

O. Vávra, W. Pfaff, and Ch. Strunk

Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2009

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We present a utilization of the inverse proximity effect in superconductor-ferromagnet (S-F) bilayer to generate lateral Josephson junctions. The weak link is created by a Pd0.95Fe0.05 strip across a Nb bridge. Close to TC and in perpendicular magnetic field the junctions exhibit a modulation of the critical current IC(B) similar to a Fraunhofer interference pattern which proves the dc Josephson effect. The structure contains three weak links (two different areas) in series which result in the observation of two periods scalable with the areas penetrated by magnetic flux. Measurements of Shapiro steps prove the presence of the ac Josephson effect.
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74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Manipulation of the magnetic configuration of (Ga,Mn)As nanostructures

J. A. Haigh, M. Wang, A. W. Rushforth, E. Ahmad, K. W. Edmonds, R. P. Campion, C. T. Foxon, and B. L. Gallagher

Appl. Phys. Lett. 95, 062502 (2009); http://dx.doi.org/10.1063/1.3200242 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2009

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We have studied the magnetic reversal of L-shaped nanostructures fabricated from (Ga,Mn)As. The strain relaxation due to the lithographic patterning results in each arm having a uniaxial magnetic anisotropy. Our analysis confirms that the magnetic reversal takes place via a combination of coherent rotation and domain wall propagation with the domain wall positioned at the corner of the device at intermediate stages of the magnetic hysteresis loops. The domain wall energy can be extracted from our analysis. Such devices have found implementation in studies of current induced domain wall motion and have the potential for application as nonvolatile memory elements.
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81.16.Rf Micro- and nanoscale pattern formation
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.60.Ch Domain walls and domain structure
62.25.-g Mechanical properties of nanoscale systems
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors

Accurate determination of the magnetic anisotropy in cluster-assembled nanostructures

Alexandre Tamion, Matthias Hillenkamp, Florent Tournus, Edgar Bonet, and Véronique Dupuis

Appl. Phys. Lett. 95, 062503 (2009); http://dx.doi.org/10.1063/1.3200950 (3 pages) | Cited 19 times

Online Publication Date: 10 August 2009

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The simultaneous triple adjustment of experimental magnetization curves under different conditions is shown to allow the unambiguous and consistent determination of both the magnetic particle size distribution and anisotropy for granular nanostructures of Co clusters embedded in protective matrices. The importance of interface effects resulting in magnetically dead layers is demonstrated.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
75.75.-c Magnetic properties of nanostructures

Double ferromagnetic resonance in nanowire arrays

Louis-Philippe Carignan, Vincent Boucher, Toshiro Kodera, Christophe Caloz, Arthur Yelon, and David Ménard

Appl. Phys. Lett. 95, 062504 (2009); http://dx.doi.org/10.1063/1.3194296 (3 pages) | Cited 9 times

Online Publication Date: 10 August 2009

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Microstrip line measurements are used to determine the frequency dependent microwave response of 40 nm diameter CoFeB ferromagnetic nanowire arrays, with external static applied field parallel to the nanowire axis. The ferromagnetic resonance (FMR) response of the wires is obtained for applied fields below and above magnetization saturation. For applied magnetic fields above saturation, a single FMR peak is observed, while below saturation, two sets of peaks are obtained. The two FMR peaks below saturation are associated with two magnetization populations, one for nanowires with upward magnetization and one with downward magnetization. A model based on a Maxwell–Garnett homogenization procedure has been established and used to predict the frequency response of the FMR peaks. There is good agreement between the model and experimental results.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.40.Az Waveguides, transmission lines, striplines
75.50.Bb Fe and its alloys

Density functional study on ferromagnetism in nitrogen-doped anatase TiO2

J. G. Tao, L. X. Guan, J. S. Pan, C. H. A. Huan, L. Wang, J. L. Kuo, Z. Zhang, J. W. Chai, and S. J. Wang

Appl. Phys. Lett. 95, 062505 (2009); http://dx.doi.org/10.1063/1.3204463 (3 pages) | Cited 27 times

Online Publication Date: 10 August 2009

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We report first principles calculations on the magnetism and electronic structures for nitrogen-doped anatase TiO2 (N:TiO2). Our calculations indicate that magnetic state is the ground state for N:TiO2 systems. An isolated N atom produces a total magnetic moment of 1.00μB and introduces spin-polarized 2p states in the band gap. The origin of the magnetic moments is the holes in N 2p π band of the N dopant. Several doping configurations studied suggest the existence of ferromagnetic coupling between N dopants. The ferromagnetism in N:TiO2 can be attributed to the hole-mediated double exchange through the strong p-p interaction between N and O.
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75.30.Cr Saturation moments and magnetic susceptibilities
72.25.Dc Spin polarized transport in semiconductors
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.30.Et Exchange and superexchange interactions

Microwave assisted magnetization reversal in single domain nanoelements

H. T. Nembach, H. Bauer, J. M. Shaw, M. L. Schneider, and T. J. Silva

Appl. Phys. Lett. 95, 062506 (2009); http://dx.doi.org/10.1063/1.3196556 (3 pages) | Cited 13 times

Online Publication Date: 11 August 2009

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We studied the microwave assisted magnetic reversal of 65×71 nm2 elliptical Ni80Fe20 nanomagnets. Hysteresis curves were measured by magneto-optical Kerr effect for a range of microwave frequencies and amplitudes. The coercive field Hc was reduced by 26% for an rf field of 0.08Hc when the microwave frequency coincided with the minimum of the experimentally determined ferromagnetic resonance frequency with varying dc field. The experimental results for the fractional reduction in Hc with rf field amplitude are in good agreement with numerical simulations for an array of interacting macrospins with a physically realistic shape anisotropy distribution.
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75.60.Jk Magnetization reversal mechanisms
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

In situ fabrication of cobalt-doped SrFe2As2 thin films by using pulsed laser deposition with excimer laser

Eun-Mi Choi, Soon-Gil Jung, Nam Hoon Lee, Young-Seung Kwon, Won Nam Kang, Dong Ho Kim, Myung-Hwa Jung, Sung-Ik Lee, and Liling Sun

Appl. Phys. Lett. 95, 062507 (2009); http://dx.doi.org/10.1063/1.3204457 (3 pages) | Cited 17 times

Online Publication Date: 12 August 2009

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The remarkably high superconducting transition temperature and upper critical field of iron (Fe)-based layered superconductors, despite ferromagnetic material base, open the prospect for superconducting electronics. However, success in superconducting electronics has been limited because of difficulties in fabricating high-quality thin films. We report the growth of high-quality c-axis-oriented cobalt (Co)-doped SrFe2As2 thin films with bulk superconductivity by using an in situ pulsed laser deposition technique with a 248 nm wavelength KrF excimer laser and an arsenic (As)-rich phase target. The temperature and field dependences of the magnetization showing strong diamagnetism and transport critical current density with superior Jc-H performance are reported. These results provide necessary information for practical applications of Fe-based superconductors.
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81.15.Fg Pulsed laser ablation deposition
74.78.-w Superconducting films and low-dimensional structures
74.25.Op Mixed states, critical fields, and surface sheaths
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Sv Critical currents
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
74.25.Ha Magnetic properties including vortex structures and related phenomena

Giant magnetic anisotropy changes in Sr2CrReO6 thin films on BaTiO3

F. D. Czeschka, S. Geprägs, M. Opel, S. T. B. Goennenwein, and R. Gross

Appl. Phys. Lett. 95, 062508 (2009); http://dx.doi.org/10.1063/1.3200236 (3 pages) | Cited 5 times

Online Publication Date: 13 August 2009

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The integration of ferromagnetic and ferroelectric materials into hybrid heterostructures yields multifunctional systems with improved or novel functionality. We here report on the structural, electronic, and magnetic properties of the ferromagnetic double perovskite Sr2CrReO6, grown as epitaxial thin film onto ferroelectric BaTiO3. As a function of temperature, the crystal-structure of BaTiO3 undergoes phase transitions, which induce qualitative changes in the magnetic anisotropy of the ferromagnet. We observe abrupt changes in the coercive field of up to 1.2 T along with resistance changes of up to 6.5%. These results are attributed to the high sensitivity of the double perovskites to mechanical deformation.
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75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
77.80.B- Phase transitions and Curie point
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
73.61.Ng Insulators
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.40.Lm Deformation, plasticity, and creep
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Tunable magnetic and transport properties of single crystalline (Co, Ga)-codoped ZnO films

Zhonglin Lu, Hua-Shu Hsu, Yonhua Tzeng, Fengming Zhang, Youwei Du, and Jung-Chun-Andrew Huang

Appl. Phys. Lett. 95, 062509 (2009); http://dx.doi.org/10.1063/1.3204016 (3 pages) | Cited 2 times

Online Publication Date: 13 August 2009

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A series of metallic (Co, Ga)-codoped ZnO single crystalline films have been grown by molecular beam epitaxy. All of the films exhibit metallic conducting behavior and high free carrier concentrations. Besides room temperature ferromagnetism, the anomalous Hall effect due to spin-orbit interaction was also found. Both the saturation magnetization and anomalous Hall effect can be tuned by the carrier concentration or conductivity, revealing that the ferromagnetism is carrier mediated in (Co, Ga)-codoped ZnO films. Our experimental observations are consistent with the recent theoretical description of carrier mediated magnetism in Co doped ZnO.
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72.20.My Galvanomagnetic and other magnetotransport effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
68.55.ag Semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Josephson effect between electron-doped and hole-doped iron pnictide single crystals

Xiaohang Zhang, Shanta R. Saha, Nicholas P. Butch, Kevin Kirshenbaum, Johnpierre Paglione, Richard L. Greene, Yong Liu, Liqin Yan, Yoon Seok Oh, Kee Hoon Kim, and Ichiro Takeuchi

Appl. Phys. Lett. 95, 062510 (2009); http://dx.doi.org/10.1063/1.3205123 (3 pages) | Cited 11 times

Online Publication Date: 14 August 2009

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We have observed the Josephson effect in junctions formed between single crystals of SrFe1.74Co0.26As2 and Ba0.23K0.77Fe2As2. The ac Josephson effect was observed under microwave irradiation in the I-V characteristics. By applying an in-plane magnetic field, the critical current is completely modulated and shows a relatively symmetric diffraction pattern consistent with the intermediate junction limit. The observation of the Josephson effect in the p-n bicrystal structure not only has significant implications for designing phase-sensitive junctions to probe the pairing symmetry of iron pnictide superconductors, but also represents an important step in developing all iron pnictide devices for applications.
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74.50.+r Tunneling phenomena; Josephson effects
72.30.+q High-frequency effects; plasma effects
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
74.25.Sv Critical currents
74.25.F- Transport properties

Electrical detection of microwave assisted magnetization switching in a Permalloy microstrip

Xiaolong Fan, Y. S. Gui, A. Wirthmann, G. Williams, Desheng Xue, and C.-M. Hu

Appl. Phys. Lett. 95, 062511 (2009); http://dx.doi.org/10.1063/1.3200239 (3 pages) | Cited 8 times

Online Publication Date: 14 August 2009

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Microwave assisted magnetization switching has been investigated in a nonelliptic Permalloy microstrip, using radio frequency magnetic fields h applied in-plane perpendicular to the long axis of the strip. In low power excitations, Hs decreases almost linearly with increasing h; this can be qualitatively understood by introducing an susceptibility χyy that links the dynamic magnetization inside the microstip to the h field outside the microstip. However, at high frequencies, Hs no longer decrease with increasing h when this latter field exceeds a critical value. We suppose such “saturation” effects could attribute to the nonlinear ferromagnetic resonance caused by high power excitations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.40.Dc Microwave circuits
75.50.Bb Fe and its alloys
84.40.Az Waveguides, transmission lines, striplines
75.30.Cr Saturation moments and magnetic susceptibilities
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

An investigation of the magnetic state dependent low frequency noise in magnetic tunnel junctions

Feng Guo, Greg McKusky, and E. Dan Dahlberg

Appl. Phys. Lett. 95, 062512 (2009); http://dx.doi.org/10.1063/1.3205476 (3 pages) | Cited 5 times

Online Publication Date: 14 August 2009

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The low frequency noise in magnetic tunnel junctions was studied as a function of applied magnetic field. In magnetic states where the magnetization is reversing, the measurement indicates a 1/f2 spectrum whereas at all other applied fields a 1/f spectrum is observed. The 1/f2 spectra are found to be an artifact of the magnetic after effect. Without the artificial influence of the magnetic after effect, only 1/f spectra are observed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.60.Lr Magnetic aftereffects

Strong anisotropy of magnetization and sign reversion of ordinary Hall coefficient in single crystal Ge1−xMnx magnetic semiconductor films

J. X. Deng, Y. F. Tian, S. M. He, H. L. Bai, T. S. Xu, S. S. Yan, Y. Y. Dai, Y. X. Chen, G. L. Liu, and L. M. Mei

Appl. Phys. Lett. 95, 062513 (2009); http://dx.doi.org/10.1063/1.3206664 (3 pages) | Cited 8 times

Online Publication Date: 14 August 2009

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Epitaxial single-crystal Ge1−xMnx ferromagnetic-semiconductor films were fabricated on Ge(001) substrates by molecular beam epitaxy. All the samples are ferromagnetic and have strong magnetic anisotropy indicated by different magnetization in plane and out of plane. The electrical transport of the films obeys Efros variable range hopping law in the low temperature range. Interestingly, a negative coefficient of the ordinary Hall effect of p-type carriers was found in the variable range hopping at low temperature. Anomalous Hall effect in Ge0.949Mn0.051 film was observed below the Curie temperature, indicating the carrier-mediated intrinsic ferromagnetism.
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75.30.Gw Magnetic anisotropy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
73.61.Le Other inorganic semiconductors
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