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5 Sep 2011

Volume 99, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 99, 103701 (2011); http://dx.doi.org/10.1063/1.3633066 (3 pages)

Yinan Zhang, David J. S. Birch, and Yu Chen
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Ferromagnetic resonance in Y3Fe5O12 nanofibers

A. Jalalian, M. S. Kavrik, S. I. Khartsev, and A. M. Grishin

Appl. Phys. Lett. 99, 102501 (2011); http://dx.doi.org/10.1063/1.3633351 (3 pages) | Cited 2 times

Online Publication Date: 6 September 2011

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Continuous bead-free polycrystalline yttrium iron garnet (YIG) nanofibers 100 μm long and 50-100 nm in diameter were sintered by sol-gel calcination assisted electrospinning. Room temperature ferromagnetism in YIG fibers is indicated by a well formed M-H hysteresis loop with about 70% of remnant magnetization to the saturated value reached at 150 Oe. Broad band microwave spectroscopy revealed strong asymmetry of ferromagnetic resonance lines that conforms to a three orders of magnitude shape aspect ratio of YIG nanofibers.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Cd Fabrication of magnetic nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials

Rapid thermal annealing study of magnetoresistance and perpendicular anisotropy in magnetic tunnel junctions based on MgO and CoFeB

Wei-Gang Wang, Stephen Hageman, Mingen Li, Sunxiang Huang, Xiaoming Kou, Xin Fan, John Q. Xiao, and C. L. Chien

Appl. Phys. Lett. 99, 102502 (2011); http://dx.doi.org/10.1063/1.3634026 (3 pages) | Cited 7 times

Online Publication Date: 6 September 2011

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The tunneling magnetoresistance and perpendicular magnetic anisotropy in CoFeB(1.1-1.2 nm)/MgO/CoFeB(1.2-1.7 nm) junctions were found to be very sensitively dependent on annealing time. During annealing at a given temperature, decay of magnetoresistance occurs much earlier compared to junctions with in-plane magnetic anisotropy. Through a rapid thermal annealing study, the decrease of magnetoresistance is found to be associated with the degradation of perpendicular anisotropy, instead of impurity diffusion as observed in common in-plane junctions. The origin of the evolution of perpendicular anisotropy as well as possible means to further enhance tunneling magnetoresistance is discussed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.30.Gw Magnetic anisotropy
61.72.Cc Kinetics of defect formation and annealing

Non-collinear magnetization configuration in interlayer exchange coupled magnetic thin films

J. Choi, B.-C. Min, J.-Y. Kim, B.-G. Park, J. H. Park, Y. S. Lee, and K.-H. Shin

Appl. Phys. Lett. 99, 102503 (2011); http://dx.doi.org/10.1063/1.3634027 (3 pages) | Cited 2 times

Online Publication Date: 6 September 2011

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Element specific magnetic hysteresis loops of the interlayer exchange coupled CoFeB/Ru/[Co/Ni]4 structure were measured utilizing x-ray magnetic circular dichroism. It was found that the Co/Ni multilayer and the CoFeB layer have Ru thickness dependent oscillatory interlayer coupling. Due to its interlayer coupling with the perpendicularly magnetized Co/Ni multilayer, the CoFeB magnetization direction is slightly tilted out-of-plane from its in-plane magnetic easy axis. Quantitative measurements show that the tilting angle is small (<12°) and that a small in-plane magnetic field (∼50 Oe) applied to this structure will result in a completely in-plane CoFeB magnetization.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects

Irradiation enhanced paramagnetism on graphene nanoflakes

Andreas Ney, Pagona Papakonstantinou, Ajay Kumar, Nai-Gui Shang, and Nianhua Peng

Appl. Phys. Lett. 99, 102504 (2011); http://dx.doi.org/10.1063/1.3628245 (3 pages) | Cited 7 times

Online Publication Date: 6 September 2011

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We have studied the magnetization of vertically aligned graphene nanoflakes irradiated with nitrogen ions of 100 KeV energy and doses in the range 1011–1017 ions/cm2. The non-irradiated graphene nanoflakes show a paramagnetic contribution, which is increased progressively by ion irradiation at low doses up to 1015/cm2. However, further increase on implantation dose reduces the magnetic moment which coincides with the onset of amorphization as verified by both Raman and x-ray photoelectron spectroscopic data. Overall, our results demonstrate the absence of ferromagnetism on either implanted or unimplanted samples from room temperature down to a temperature of 5 K.
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75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.30.Na Fullerenes and related materials
75.30.Cr Saturation moments and magnetic susceptibilities
61.48.Gh Structure of graphene

Unidirectional anisotropy in the spin pumping voltage in yttrium iron garnet/platinum bilayers

L. H. Vilela-Leão, C. Salvador, A. Azevedo, and S. M. Rezende

Appl. Phys. Lett. 99, 102505 (2011); http://dx.doi.org/10.1063/1.3631683 (3 pages) | Cited 7 times

Online Publication Date: 6 September 2011

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Detailed measurements of the dc voltage generated in a thin Pt layer deposited on films of yttrium iron garnet (YIG) have been carried out to study the spin pumping effect produced by magnetostatic (MS) modes excited by a microwave field. In relatively thick YIG films the modes are far apart so that one can identify clearly the spin pumping voltage in VSP produced by each MS mode. We have discovered that when the sputter deposition of the thin Pt layer is made on the YIG film magnetized by a static magnetic field, VSP exhibits a strong unidirectional anisotropy.
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75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
75.30.Ds Spin waves

Manipulation of magnetic coercivity of Fe film in Fe/BaTiO3 heterostructure by electric field

G. Venkataiah, Y. Shirahata, M. Itoh, and T. Taniyama

Appl. Phys. Lett. 99, 102506 (2011); http://dx.doi.org/10.1063/1.3628464 (3 pages) | Cited 11 times

Online Publication Date: 6 September 2011

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The manipulation of magnetism at Fe/BaTiO3 interfaces is demonstrated via lattice distortion induced by thermal and electrical means. We find that the magnetic coercivity shows similar electric field dependence for positive and negative electric fields in the tetragonal phase of BaTiO3, whereas those in the orthorhombic and rhombohedral phases vary asymmetrically with respect to the polarity. The temperature dependent magnetization also reveals that the effect has its origin in the strong magnetoelastic coupling at the interface. The underlying mechanisms of the electric field dependence of the coercivity are discussed, associated with the different ferroelectric poling processes of BaTiO3.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
77.80.-e Ferroelectricity and antiferroelectricity
75.80.+q Magnetomechanical effects, magnetostriction

Spin-torque-driven ballistic precessional switching with 50 ps impulses

O. J. Lee, D. C. Ralph, and R. A. Buhrman

Appl. Phys. Lett. 99, 102507 (2011); http://dx.doi.org/10.1063/1.3635782 (3 pages) | Cited 8 times

Online Publication Date: 7 September 2011

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We demonstrate reliable spin-torque-driven ballistic precessional switching using 50 ps current impulses in a spin-valve device that includes both in-plane and out-of-plane spin polarizers. Different threshold currents as the function of switching direction and current polarity enable the final orientation of the magnetic free layer to be steered, in accord with a macrospin analysis, by the sign of the pulse, eliminating the need for read-before-write toggle operation. The pulse amplitude windows for this deterministic operation are wider and more symmetric as a function of current polarity for shorter impulses, while inhomogeneous fringe fields from the polarizers lead to asymmetries as a function of current direction.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Unusual high-temperature ferromagnetism of PbPd0.81Co0.19O2 nanograin film

H. L. Su, S. Y. Huang, Y. F. Chiang, J. C. A. Huang, C. C. Kuo, Y. W. Du, Y. C. Wu, and R. Z. Zuo

Appl. Phys. Lett. 99, 102508 (2011); http://dx.doi.org/10.1063/1.3634070 (3 pages) | Cited 2 times

Online Publication Date: 8 September 2011

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Single-phase PbPd0.81Co0.19O2 film with a body-centered orthorhombic structure was prepared using the sol-gel spin-coating technique and an oxidation treatment. Film resistivity has a power dependence on temperature. The insulator-metal transition temperature was 358 K, markedly higher than the reported values of similar material systems. Ferromagnetism and superparamagnetism coexisted in the film and the ferromagnetism persisted up to 380 K. As temperature increased, the notable increasing tendencies were found for the film’s saturation magnetization and for the magnetic field where saturation magnetization decreases abruptly. The special spin gapless band structure and the film’s nanograin microstructure are likely responsible for these interesting properties.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Cd Fabrication of magnetic nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Ho substitution suppresses collinear Dy spin order and enhances polarization in DyMnO3

N. Zhang, Y. Y. Guo, L. Lin, S. Dong, Z. B. Yan, X. G. Li, and J.-M. Liu

Appl. Phys. Lett. 99, 102509 (2011); http://dx.doi.org/10.1063/1.3636399 (3 pages) | Cited 9 times

Online Publication Date: 9 September 2011

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The multiferroic behaviors of Dy1−xHoxMnO3 are investigated in order to reveal the effects of Ho-substitution on the independent collinear Dy spin order and ferroelectric polarization at low temperature. It is demonstrated that a partial Ho-substitution of Dy ions significantly suppresses the independent Dy spin order at low temperature on one hand, and maintains the R-Mn spin coupling on the other hand, thus leading to a remarkable enhancement of the polarization at low temperature.
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77.22.Ej Polarization and depolarization
75.85.+t Magnetoelectric effects, multiferroics
75.80.+q Magnetomechanical effects, magnetostriction
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