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27 Jun 2011

Volume 98, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 98, 263101 (2011); http://dx.doi.org/10.1063/1.3587576 (3 pages)

Jing Ye, Yu Zhao, Libin Tang, Li-Miao Chen, C. M. Luk, S. F. Yu, S. T. Lee, and S. P. Lau
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Improved tunneling magnetoresistance in (Ga,Mn)As/AlOx/CoFeB magnetic tunnel junctions

G. Q. Yu, L. Chen, Syed Rizwan, J. H. Zhao, K. XU, and X. F. Han

Appl. Phys. Lett. 98, 262501 (2011); http://dx.doi.org/10.1063/1.3603946 (3 pages)

Online Publication Date: 27 June 2011

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We fabricated (Ga,Mn)As/AlOx/Co40Fe40B20 magnetic tunnel junctions with ferromagnetic semiconductor/insulator/ferromagnetic metal (S/I/F) structure. The treatments of pre-annealing and post-plasma cleaning on the (Ga,Mn)As film were introduced before the growth of the subsequent layers. A high tunneling magnetoresistance (TMR) ratio of 101% is achieved at 2 K, and the spin polarization of (Ga,Mn)As, P = 56.8%, is deduced from Jullière’s formula. The improved TMR ratio is primarily due to the improved magnetism of (Ga,Mn)As layer by low-temperature annealing and cleaned interface between (Ga,Mn)As and AlOx attained by subsequent plasma cleaning process.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.25.Mk Spin transport through interfaces
81.05.Ea III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys
75.50.Dd Nonmetallic ferromagnetic materials

Ferrohydrodynamic relaxometry for magnetic particle imaging

P. W. Goodwill, A. Tamrazian, L. R. Croft, C. D. Lu, E. M. Johnson, R. Pidaparthi, R. M. Ferguson, A. P. Khandhar, K. M. Krishnan, and S. M. Conolly

Appl. Phys. Lett. 98, 262502 (2011); http://dx.doi.org/10.1063/1.3604009 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2011

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The ferrohydrodynamic properties of magnetic nanoparticles govern resolution and signal strength in magnetic particle imaging (MPI), a medical imaging modality with applications in small animals and humans. Here, we discuss the development and key results of a magnetic particle relaxometer that measures the core diameter and relaxation constant of magnetic nanoparticles. This instrument enables us to directly measure the one-dimensional MPI point spread function. To elucidate our results, we develop a simplified ferrohydrodynamic model that assumes nanoparticles respond to time varying magnetic fields according to a Debeye model of Brownian relaxation, which we verify with experimental data.
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87.85.Pq Biomedical imaging
87.85.Rs Nanotechnologies-applications
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Jn Dynamics of magnetic nanoparticles
47.65.Cb Magnetic fluids and ferrofluids

Local and non-local magnetoresistance with spin precession in highly doped Si

T. Sasaki, T. Oikawa, T. Suzuki, M. Shiraishi, Y. Suzuki, and K. Noguchi

Appl. Phys. Lett. 98, 262503 (2011); http://dx.doi.org/10.1063/1.3604010 (3 pages) | Cited 1 time

Online Publication Date: 28 June 2011

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We have demonstrated comparison of spin accumulation voltages in local and non-local (NL) magnetoresistance measurements without any spurious megnetoresistive signals. The spin transport length in a local measurement was larger than that in a NL measurement. An intensity of the local signals was explained by a conductivity mismatch theory. Depending on the relative magnetic configurations, Hanle-type spin precession signals in the local and the NL schemes showed a clear difference in signal shapes. The local transporting spins are accelerated in the direction of the electric field, and precess around the direction of the magnetic field under the detector electrode.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Cw Elemental semiconductors
72.25.Dc Spin polarized transport in semiconductors

Electrical control of reversible and permanent magnetization reorientation for magnetoelectric memory devices

Tao Wu (吴涛), Alexandre Bur, Kin Wong, Ping Zhao, Christopher S. Lynch, Pedram Khalili Amiri, Kang L. Wang, and Gregory P. Carman

Appl. Phys. Lett. 98, 262504 (2011); http://dx.doi.org/10.1063/1.3605571 (3 pages) | Cited 10 times

Online Publication Date: 30 June 2011

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We report giant reversible and permanent magnetic anisotropy reorientation between two perpendicular easy axes in a magnetoelectric polycrystalline Ni thin film and (011) oriented [Pb(Mg1/3Nb2/3)O3](1−x)-[PbTiO3]x (PMN-PT) heterostructure. The PMN-PT is partially poled prior to Ni film deposition to provide a remanent strain bias. Following Ni deposition and full poling of the sample, two giant remanent strains of equal and opposite values are used to reversibly and permanently reorient the magnetization state of the Ni film. These experimental results are integrated into micromagnetic simulation to demonstrate the usefulness of this approach for magnetoelectric based magnetic random access memory.
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75.30.Gw Magnetic anisotropy
77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics

Epitaxial growth of Heusler alloy Co2MnSi/MgO heterostructures on Ge(001) substrates

Gui-fang Li, Tomoyuki Taira, Ken-ichi Matsuda, Masashi Arita, Tetsuya Uemura, and Masafumi Yamamoto

Appl. Phys. Lett. 98, 262505 (2011); http://dx.doi.org/10.1063/1.3605675 (3 pages) | Cited 1 time

Online Publication Date: 30 June 2011

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We prepared Heusler alloy Co2MnSi/MgO heterostructures on single-crystal Ge(001) substrates through magnetron sputtering for Co2MnSi and electron beam evaporation for MgO as a promising candidate for future generation spin-based functional devices. Structural investigations showed that the Co2MnSi/MgO heterostructure was grown epitaxially on a Ge(001) substrate with extremely smooth and abrupt interfaces and showed the L21 structure for the Co2MnSi film. Furthermore, a sufficiently high saturation magnetization (μs) value of 5.1 µB/f.u. at 10 K, which is close to the theoretically predicted μs of 5.0 µB/f.u. for half-metallic Co2MnSi, was obtained for prepared Co2MnSi films.
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81.15.Cd Deposition by sputtering
81.15.Dj E-beam and hot filament evaporation deposition
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.A- Nucleation and growth

Temperature-dependent magnetic anisotropies in epitaxial Fe/CoO/MgO(001) system studied by the planar Hall effect

W. N. Cao, J. Li, G. Chen, J. Zhu, C. R. Hu, and Y. Z. Wu

Appl. Phys. Lett. 98, 262506 (2011); http://dx.doi.org/10.1063/1.3606531 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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Exchange-induced in-plane magnetic anisotropies in a single-crystalline Fe/CoO/MgO(001) system were quantitatively investigated using the planar Hall effect as a function of temperature. Field cooling can induce a strong uniaxial anisotropy in Fe film with the easy axis along the CoO〈110〉 directions close to the cooling field direction. The exchange coupling also induces a 4-fold anisotropy with the easy axis along the CoO〈100〉 directions. Our results prove that the strong magneto-crystalline anisotropy of CoO antiferromagnetic spin plays a significant role in exchange-induced anisotropy.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions

Direct probing magnetization reversal of exchange-coupled-composite media by x-ray magnetic circular dichroism

Hao-Cheng Hou, Dieter Suess, Jung-Wei Liao, Meng-Shian Lin, Hong-Ji Lin, Fan-Hsiu Chang, and Chih-Huang Lai

Appl. Phys. Lett. 98, 262507 (2011); http://dx.doi.org/10.1063/1.3603945 (3 pages) | Cited 3 times

Online Publication Date: 1 July 2011

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X-ray magnetic circular dichroism (XMCD) was used to directly probe the depth-dependent magnetization reversal of CoPtCr-SiO2-based exchange-coupled-composite media with laminated soft layers. A thin Fe-marker layer in the soft layer was used as the indicator of local magnetization. Element-specific XMCD loops of Fe-marker layers confirmed the transition of the magnetization reversal from rigid magnets to exchange-spring magnets with increasing thickness of the soft layer. The micromagnetic simulations revealed the importance of the reduced exchange constant (Asoft) by laminating the soft layer for domain-wall assisting reversal. By comparing XMCD loops with simulations, we can deduce the effective Asoft.
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75.60.Jk Magnetization reversal mechanisms
75.78.Cd Micromagnetic simulations
78.20.Ls Magneto-optical effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Field tunable localization of spin waves in antidot arrays

C.-L. Hu, R. Magaraggia, H.-Y. Yuan, C. S. Chang, M. Kostylev, D. Tripathy, A. O. Adeyeye, and R. L. Stamps

Appl. Phys. Lett. 98, 262508 (2011); http://dx.doi.org/10.1063/1.3606556 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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We show that magnetic spin wave resonance modes in an antidot patterned array are sensitive to small changes in the magnetic configuration near dots, resulting in strong localization effects as the field is increased. Frequencies measured using ferromagnetic resonance from an antidot array patterned from a NiFe/IrMn bilayer are interpreted using micromagnetic calculations, and it is shown that the observed field dependence of the resonance response can be attributed to strong interdot localization of spin waves. This field tunable localization is created by stray fields produced by magnetic poles at the dot surfaces.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.78.Cd Micromagnetic simulations
75.75.-c Magnetic properties of nanostructures

Iron-chalcogenide FeSe0.5Te0.5 coated superconducting tapes for high field applications

Weidong Si, Juan Zhou, Qing Jie, Ivo Dimitrov, V. Solovyov, P. D. Johnson, J. Jaroszynski, V. Matias, C. Sheehan, and Qiang Li

Appl. Phys. Lett. 98, 262509 (2011); http://dx.doi.org/10.1063/1.3606557 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe0.5Te0.5 layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1 × 104 A/cm2) at about 4.2 K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
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