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17 Oct 2011

Volume 99, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 99, 163301 (2011); http://dx.doi.org/10.1063/1.3651509 (3 pages)

Jonathan E. Allen, Kevin G. Yager, Htay Hlaing, Chang-Yong Nam, Benjamin M. Ocko, and Charles T. Black
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Mode selective parametric excitation of spin waves in a Ni81Fe19 microstripe

T. Brächer, P. Pirro, B. Obry, B. Leven, A. A. Serga, and B. Hillebrands

Appl. Phys. Lett. 99, 162501 (2011); http://dx.doi.org/10.1063/1.3651506 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2011

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We present the experimental observation of parallel parametric amplification of selected thermal spin-wave modes in a transversally magnetized Ni81Fe19 microstripe. By employing Brillouin light scattering microscopy, we identify the dominant group, i.e., the spin-wave mode that is preferentially amplified. Due to the existing spin-wave quantization in the system, it is possible to select one specific mode to be parametrically excited by changing the bias magnetic field. This gives access to transversal spin-wave eigenmodes of the stripe which are promising for spin-wave information processing and also to modes localized at the stripe edges.
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75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Spin pumping by parametrically excited short-wavelength spin waves

H. Kurebayashi, O. Dzyapko, V. E. Demidov, D. Fang, A. J. Ferguson, and S. O. Demokritov

Appl. Phys. Lett. 99, 162502 (2011); http://dx.doi.org/10.1063/1.3652911 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2011

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We use both parallel and perpendicular parametric pumping techniques to excite short-wavelength spin waves in an yttrium iron garnet film and study the spin current generation from spin waves excited by these pumping methods with the help of the inverse spin-Hall effect in the adjacent Pt layer. We observed clear spin current generations for these pumping techniques and find that the efficiency is nearly independent of the magnitude and the direction of the wave vectors of excited spin waves. These experimental results are important for future spintronic devices operated by short-wavelength spin waves.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
72.25.Pn Current-driven spin pumping
75.76.+j Spin transport effects

Micromagnetic modelling of L10-FePt/Ag/L10-FePt pseudo spin valves

P. Ho, R. F. L. Evans, R. W. Chantrell, G. C. Han, G. M. Chow, and J. S. Chen

Appl. Phys. Lett. 99, 162503 (2011); http://dx.doi.org/10.1063/1.3653290 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2011

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A micromagnetic bilayer model, based on the Landau-Lifshitz-Bloch equation, was utilized to study the magnetic, reversal, and spin transport properties of MgO/L10-FePt/Ag/L10-FePt pseudo spin valves. The model simulates a granular bilayer FePt structure and the effects of the Ag spacer were controlled by varying the interlayer exchange strength. Simulation results showed that the reversal of the FePt layers proceeded via reversed domain formation and propagation. Stray fields emanating from the top soft FePt layer reduced the nucleation field of the bottom FePt locally, resulting in the preferential formation of reversed domains at adjacent sites of the bottom hard FePt layer.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.78.Cd Micromagnetic simulations
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.76.+j Spin transport effects
75.60.Jk Magnetization reversal mechanisms

Magnetocaloric effect contributed by in situ dual-phase structure in the Gd-Co-Al alloy

H. Fu, Q. Zheng, and M. X. Wang

Appl. Phys. Lett. 99, 162504 (2011); http://dx.doi.org/10.1063/1.3652913 (3 pages)

Online Publication Date: 18 October 2011

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In many cases, the presence of secondary phase will deteriorate the magnetocaloric effect of materials due to the difference in magnetic properties. However, the alloy with in situ dual-phase structure and good magnetocaloric effect was found in the pseudo-binary GdCo2-GdAl2 system. Experiments revealed that the GdCo0.65Al1.35 alloy comprised the primary terminal GdAl2 phase and the secondary intermediate GdCo0.74Al1.26 phase. Both of them ordered at 70 K simultaneously. Large magnetic entropy change and relative cooling power of 11.0 J/kg K and 638 J/kg for 0–50 kOe field changes, respectively, were obtained due to the contribution of both GdAl2 and GdCo0.74Al1.26 phases.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Mode conversion by symmetry breaking of propagating spin waves

P. Clausen, K. Vogt, H. Schultheiss, S. Schäfer, B. Obry, G. Wolf, P. Pirro, B. Leven, and B. Hillebrands

Appl. Phys. Lett. 99, 162505 (2011); http://dx.doi.org/10.1063/1.3650256 (3 pages) | Cited 5 times

Online Publication Date: 18 October 2011

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We study spin-wave transport in a microstructured Ni81Fe19 waveguide exhibiting broken translational symmetry. We observe the conversion of a beam profile composed of symmetric spin-wave width modes with odd numbers of antinodes n = 1, 3,… into a mixed set of symmetric and asymmetric modes. Due to the spatial homogeneity of the exciting field along the used microstrip antenna, quantized spin-wave modes with an even number n of antinodes across the stripe’s width cannot be directly excited. We show that a break in translational symmetry may result in a partial conversion of even spin-wave waveguide modes.
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75.30.Ds Spin waves

Josephson amplifier for qubit readout

Baleegh Abdo, Flavius Schackert, Michael Hatridge, Chad Rigetti, and Michel Devoret

Appl. Phys. Lett. 99, 162506 (2011); http://dx.doi.org/10.1063/1.3653473 (3 pages) | Cited 8 times

Online Publication Date: 18 October 2011

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We report on measurements of a Josephson amplifier (J-amp) suitable for quantum-state qubit readout in the microwave domain. It consists of two microstrip resonators which intersect at a Josephson ring modulator. A maximum gain of about 20 dB, a bandwidth of 9 MHz, and a center-frequency tunability of about 60 MHz with gain in excess of 10 dB have been attained for idler and signal of frequencies 6.4 GHz and 8.1 GHz, in accordance with theory. Maximum input power measurements of the J-amp show a relatively good agreement with theoretical prediction. We discuss how the amplifier characteristics can be improved.
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85.25.Cp Josephson devices
84.40.Az Waveguides, transmission lines, striplines
84.30.Le Amplifiers

Structural, magnetic, and magnetotransport properties of NiMnSb thin films deposited by flash evaporation

Nguyen Anh Tuan and Nguyen Phuc Duong

Appl. Phys. Lett. 99, 162507 (2011); http://dx.doi.org/10.1063/1.3651337 (3 pages)

Online Publication Date: 18 October 2011

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To date, the use of flash evaporation (FE) as a deposition technique for NiMnSb thin films has not yet been reported. In this letter, we report on NiMnSb thin films deposited on heated Si (111) substrates at 300 °C via FE. Investigations of the structural characteristics and magnetic and magnetotransport properties of these thin films show typical features of a half-metallic ferromagnetic semi-Heusler alloy. The origin of the film’s extraordinary magnetotransport behavior is examined under the perspective of spin-order levels attached to a grain-grain boundary-type structure.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
75.50.Cc Other ferromagnetic metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars

Jaivardhan Sinha, Masamitsu Hayashi, Yukiko K. Takahashi, Tomohiro Taniguchi, Maksim Drapeko, Seiji Mitani, and Kazuhiro Hono

Appl. Phys. Lett. 99, 162508 (2011); http://dx.doi.org/10.1063/1.3647771 (3 pages) | Cited 5 times

Online Publication Date: 19 October 2011

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We have studied microwave emission from a current-perpendicular-to-plane pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ga0.5Ge0.5) electrodes. Large emission amplitude exceeding 150 nV/Hz0.5, partly owing to the large magnetoresistance, and narrow generation linewidth below 10 MHz are observed. We also find that the linewidth shows significant dependence on the applied field magnitude and its angle within the film plane. A minimum in the linewidth is observed when the slope of the frequency versus current becomes near zero. This agrees with theoretical prediction that takes into account non-linear phase noise as a source for linewidth broadening.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.Np Metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Interface effects on perpendicular magnetic anisotropy for molecular-capped cobalt ultrathin films

Xianmin Zhang, Shigemi Mizukami, Takahide Kubota, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, and Terunobu Miyazaki

Appl. Phys. Lett. 99, 162509 (2011); http://dx.doi.org/10.1063/1.3651766 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2011

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The perpendicular magnetic anisotropy (PMA) of cobalt (0.5-1.8 nm) films capped separately by pentacene (Pc), fullerene (C60), and 8-hydroxyquinoline-aluminum (Alq3) are investigated. For all three series, the thickness of Co is around 0.7 nm for maximum out-of-plane coercivity. It is found that the coercivity of C60-capped films is nearly equal to that for Alq3-capped samples, although both are smaller than for Pc-capped films. The different interface effects of Co/molecules are discussed to explain this observation. This work highlights the PMA of ferromagnetic metal, which can be markedly infected depending on the nature of organic molecule.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
68.55.at Other materials

Structure and magnetic properties of ternary Tb-Fe-B nanoparticles and nanoflakes

R. M. Liu, M. Yue, W. Q. Liu, D. T. Zhang, J. X. Zhang, Z. H. Guo, and W. Li

Appl. Phys. Lett. 99, 162510 (2011); http://dx.doi.org/10.1063/1.3653256 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2011

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The structure and magnetic properties were studied for the ternary Tb-Fe-B nanoparticles and nanoflakes prepared by surfactant-aid high energy ball milling and subsequent size-selection. For the nanoparticles, significant room-temperature coercivity up to 10.6 kOe was achieved with the average particle size of 31.4 nm, but it decreases substantially to 400 Oe as the size is down to 8.2 nm. For the nanoflakes, the thickness is in the range of 50-80 nm while the length is about 1.1 μm, and high coercivity of 22.1 kOe and strong magnetic anisotropy were obtained simultaneously, indicating that the nanoflakes possess excellent permanent magnetic properties.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Bb Fe and its alloys
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.Rf Micro- and nanoscale pattern formation
81.07.Wx Nanopowders
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Electric control of magnetization relaxation in thin film magnetic insulators

Zihui Wang, Yiyan Sun, Young-Yeal Song, Mingzhong Wu, Helmut Schultheiß, John E. Pearson, and Axel Hoffmann

Appl. Phys. Lett. 99, 162511 (2011); http://dx.doi.org/10.1063/1.3654148 (3 pages) | Cited 5 times

Online Publication Date: 20 October 2011

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Control of magnetization relaxation in magnetic insulators via interfacial spin scattering is demonstrated. The experiments use nanometer-thick yttrium iron garnet (YIG)/Pt layered structures, with the Pt layer biased by an electric voltage. The bias voltage produces a spin current across the Pt thickness. As this current scatters off the YIG surface, it exerts a torque on the YIG surface spins. This torque can reduce or enhance the damping and thereby decrease or increase the ferromagnetic resonance linewidth of the YIG film, depending on the field/current configuration.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Experimental evidence of Ga-vacancy induced room temperature ferromagnetic behavior in GaN films

Basanta Roul, Mohana K. Rajpalke, Thirumaleshwara N. Bhat, Mahesh Kumar, A. T. Kalghatgi, S. B. Krupanidhi, Nitesh Kumar, and A. Sundaresan

Appl. Phys. Lett. 99, 162512 (2011); http://dx.doi.org/10.1063/1.3654151 (3 pages) | Cited 5 times

Online Publication Date: 20 October 2011

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We have grown Ga deficient GaN epitaxial films on (0001) sapphire substrate by plasma-assisted molecular beam epitaxy and report the experimental evidence of room temperature ferromagnetic behavior. The observed yellow emission peak in room temperature photoluminescence spectra and the peak positioning at 300 cm−1 in Raman spectra confirms the existence of Ga vacancies. The x-ray photoelectron spectroscopic measurements further confirmed the formation of Ga vacancies; since the N/Ga is found to be >1. The ferromagnetism is believed to originate from the polarization of the unpaired 2p electrons of N surrounding the Ga vacancy.
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75.70.Ak Magnetic properties of monolayers and thin films
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Table-like magnetocaloric effect and enhanced refrigerant capacity in Eu8Ga16Ge30-EuO composite materials

Anurag Chaturvedi, Stevce Stefanoski, Manh-Huong Phan, George S. Nolas, and Hariharan Srikanth

Appl. Phys. Lett. 99, 162513 (2011); http://dx.doi.org/10.1063/1.3654157 (3 pages) | Cited 17 times

Online Publication Date: 21 October 2011

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A large reversible magnetocaloric effect (MCE) and enhanced refrigerant capacity (RC) were observed in multiphase composite materials composed of type-I clathrate Eu8Ga16Ge30 and EuO. Eu8Ga16Ge30 undergoes two successive ferromagnetic transitions at 10 K and 35 K, and EuO exhibits a ferromagnetic transition at 75 K. A large RC of 794 J/kg for a field change of 5 T over a temperature interval of 70 K was achieved in the Eu8Ga16Ge30–EuO composite with a 40%-60% weight ratio. This is the largest value ever achieved among existing magnetocaloric materials for magnetic refrigeration in the temperature range 10 K-100 K. Adjusting the Eu8Ga16Ge30 to EuO ratio is shown to produce composites with table-like MCE, desirable for ideal Ericsson-cycle magnetic refrigeration. The excellent magnetocaloric properties of these Eu8Ga16Ge30–EuO composites make them attractive for active magnetic refrigeration in the liquid nitrogen temperature range.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetic force microscopy in the presence of a strong probe field

Inhee Lee, Jongjoo Kim, Yuri Obukhov, Palash Banerjee, Gang Xiang, Denis V. Pelekhov, Adam Hauser, Fengyuan Yang, and P. Chris Hammel

Appl. Phys. Lett. 99, 162514 (2011); http://dx.doi.org/10.1063/1.3653281 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2011

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We describe a magnetic force microscopy (MFM) imaging approach in which we take advantage of the strong, localized magnetic field of the MFM probe to deterministically modify the magnetization of the sample. This technique enables quantitative mapping of sample magnetic properties including saturation magnetization and anisotropy, a capability not generally available using conventional MFM methods. This approach yields a fruitful theoretical analysis that accurately describes representative experimental data we obtain from an isolated permalloy disk.
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07.79.Pk Magnetic force microscopes
75.30.Gw Magnetic anisotropy
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