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1 Apr 2011

Volume 109, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 109, 071101 (2011); http://dx.doi.org/10.1063/1.3562200 (10 pages)

Otwin Breitenstein, Jan Bauer, Karsten Bothe, Wolfram Kwapil, Dominik Lausch, Uwe Rau, Jan Schmidt, Matthias Schneemann, Martin C. Schubert, Jan-Martin Wagner, and Wilhelm Warta
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back to top Magnetization Dynamics, Micromagnetics, and Magnetic Imaging

Static and dynamic properties of one-dimensional linear chain of nanomagnets

J. Ding, S. Jain, and A. O. Adeyeye

J. Appl. Phys. 109, 07D301 (2011); http://dx.doi.org/10.1063/1.3535413 (3 pages) | Cited 4 times

Online Publication Date: 17 March 2011

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We have probed the dynamic and static behavior of one-dimensional linear chain of magnetostatically coupled Ni80Fe20 elements using ferromagnetic resonance (FMR) spectroscopy and magneto-optic Kerr effect measurement techniques. When compared with isolated elements of similar dimensions, we observed that both the FMR curves and magnetization reversal process of the coupled elements are strongly influenced by the strong magnetostatic interactions. We have modeled the effect of magnetostatic coupling, by extracting the demagnetizing factors for the isolated element from the experimental data using least square fitting method. Our experimental results are in good agreement with theory.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.20.Ls Magneto-optical effects
75.50.Bb Fe and its alloys
75.60.Jk Magnetization reversal mechanisms

Precessional switching by ultrashort pulse laser: Beyond room temperature ferromagnetic resonance limit

Arata Tsukamoto, Tetsuya Sato, Shingo Toriumi, and Akiyoshi Itoh

J. Appl. Phys. 109, 07D302 (2011); http://dx.doi.org/10.1063/1.3535415 (3 pages) | Cited 4 times

Online Publication Date: 17 March 2011

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Conventional pure magnetic recording schemes have a serious and unavoidable problem known as the ferromagnetic resonance (FMR) limit. Here we demonstrate a fast precessional switching via interplay of ultrafast heating by ultrashort pulse laser and large temperature dependency of magnetic resonance. In ferrimagnetic GdFeCo, when the temperature approaches the angular momentum compensation point TA, both frequency of FMR mode and the Gilbert damping parameter increase significantly. High-speed and strongly damped precessional switching was triggered with ultrafast heating of a Gd24.5Fe66.1Co9.4 across its magnetization compensation point TM up to TA, under a static applied magnetic field. To initiate and investigate the magnetization reversal, we have used an all-optical pump-probe technique employing an amplified Ti:sapphire laser system with 90 fs pulses. In particular, following the laser excitation with low pump fluence (0.9 mJ/cm2) the magnetic system relaxes back toward initial state while the rather high pump fluence (3.3 mJ/cm2) excitation induces a metastable opposite magnetic state. After the sudden heating which causes just 30% reduction of magnetization at first breakdown, consequently magnetization was started to rotate across Mz = 0 within 6 ps during first precession and finished the high damped precessional motion within few cycles into opposite direction.
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75.78.Jp Ultrafast magnetization dynamics and switching
42.62.-b Laser applications
75.50.Gg Ferrimagnetics
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.40.Gh Other heat and thermomechanical treatments
75.60.Jk Magnetization reversal mechanisms

Ultrafast demagnetization in ferromagnets and magnetic switching in nanoclusters when the number of photons is kept fixed

G. P. Zhang, G. Lefkidis, W. Hübner, and Yihua Bai

J. Appl. Phys. 109, 07D303 (2011); http://dx.doi.org/10.1063/1.3533255 (3 pages) | Cited 2 times

Online Publication Date: 18 March 2011

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Different from thermally and magnetically induced demagnetization, the laser-induced demagnetization relies on the laser photon field. However, what has been unknown is how the spin moment reduction correlates with the number of photons. Here, our first-principles calculation in ferromagnetic nickel and cobalt clusters shows that the number of photons is not the sole decisive factor for the magnetization change, contrary to earlier belief. For the same number of photons absorbed, the shorter the laser pulse, the larger the induced spin moment reduction. Besides a simple decrease in the magnetic moment, a short pulse also excites a strong coherent spin oscillation, which disappears when using a longer pulse. The longest pulse duration where we observed this oscillation is about 20 fs. Future experiments can directly test our prediction. We show that for our generic ultrafast spin-switching Λ-process on metallic nanoclusters the electronic correlations constitute a key ingredient, which allows for spin and charge separation. By selectively removing correlational channels, we gradually inhibit the magnetic switching. The dynamics proceeds far from any electronic thermal equilibrium and thus no temperature can be attributed to the system or any subsystem.
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75.78.Jp Ultrafast magnetization dynamics and switching
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.Cc Other ferromagnetic metals and alloys

Effect of antidot diameter on the dynamic response of nanoscale antidot arrays

J. Ding, D. Tripathy, and A. O. Adeyeye

J. Appl. Phys. 109, 07D304 (2011); http://dx.doi.org/10.1063/1.3535425 (3 pages) | Cited 2 times

Online Publication Date: 18 March 2011

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The dynamic response of nanoscale circular Permalloy antidot arrays in a square lattice geometry has been systematically investigated as a function of “hole” diameter using broadband ferromagnetic spectroscopy. Two main resonance modes were observed for the field applied along the lattice edge, whereas only a single main mode was observed along the diagonal of the square lattice. We also observed that the frequency of all modes can be systematically tuned by varying the antidot diameter. Our experimental results have been further validated using micromagnetic simulations.
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75.75.-c Magnetic properties of nanostructures
75.50.Bb Fe and its alloys
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Spatially resolved observation of uniform precession modes in spin-valve systems

Alexander M. Kaiser, Carsten Wiemann, Stefan Cramm, and Claus M. Schneider

J. Appl. Phys. 109, 07D305 (2011); http://dx.doi.org/10.1063/1.3535439 (3 pages) | Cited 3 times

Online Publication Date: 18 March 2011

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Using time-resolved photoemission electron microscopy, the excitation of uniform precession modes in individual domains of a weakly coupled spin–valve system has been studied. A coupling dependence of the precession frequencies has been found that can be reasonably well understood on the basis of a macrospin model. By tuning the frequency of the excitation source the uniform precession modes are excited in a resonant way.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
79.60.Jv Interfaces; heterostructures; nanostructures
78.47.J- Ultrafast spectroscopy (<1 psec)

Electrical detection of vortex states in a ferromagnetic disk using the rectifying effect

M. Goto, H. Hata, A. Yamaguchi, Y. Nakatani, T. Yamaoka, and Y. Nozaki

J. Appl. Phys. 109, 07D306 (2011); http://dx.doi.org/10.1063/1.3536390 (3 pages) | Cited 1 time

Online Publication Date: 18 March 2011

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A magnetic vortex core confined in a micron-scale magnetic disk is resonantly excited by both spin-polarized rf current and rf field. We found that rectifying voltage spectra caused by the resonance of vortex core are dependent not only on the core polarity, but also the chirality. These experimental results can be explained by analytically calculating the anisotropic magnetoresistance effect induced by the motion of the vortex core.
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75.47.Np Metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Spin torque oscillation modes of a dual magnetic tunneling junction

Yisong Zhang, Hui Zhao, Andrew Lyle, Paul A. Crowell, and Jian-Ping Wang

J. Appl. Phys. 109, 07D307 (2011); http://dx.doi.org/10.1063/1.3536538 (3 pages)

Online Publication Date: 21 March 2011

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Two coexisting spin torque oscillation (STO) modes in dual magnetic tunnel junctions with MgO barriers are observed by measuring the field-dependent power spectra. The frequency-field relation of the main STO mode is found to follow the Kittel equation at both positive and negative fields applied along the easy axis, which is consistent with spin torque oscillation of the magnetic free layer between the two MgO barriers. The second oscillation mode shows a different frequency-field relation for positive and negative applied fields, which is tentatively understood by considering the oscillation of the weakly-pinned top layer.
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75.47.Pq Other materials
72.25.-b Spin polarized transport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Analysis of volume distribution of power loss in ferrite cores

M. LoBue, V. Loyau, and F. Mazaleyrat

J. Appl. Phys. 109, 07D308 (2011); http://dx.doi.org/10.1063/1.3536792 (3 pages) | Cited 1 time

Online Publication Date: 22 March 2011

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We present a technique to estimate the inhomogeneities of magnetic loss across the section of ferrite cores under ac excitation. The technique is based on two distinct calorimetric methods that we presented elsewhere. Both methods are based on the measurement of the rate of increase of the sample temperature under adiabatic condition. The temperature ramp is recorded either measuring the sample bulk resistivity or using a platinum probe pasted on the sample surface. As an example we apply the procedure to an industrial sample of Mn–Zn ferrite under controlled sinusoidal excitation with a peak induction of 50 mT in the range between 100 kHz and 2 MHz. The results are discussed by comparison with simulations of the dissipation field profile through the sample, calculated using a finite element method (FEM) code.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Gg Ferrimagnetics

Nanomechanical torsional resonator torque magnetometry (invited)

J. P. Davis, D. Vick, P. Li, S. K. N. Portillo, A. E. Fraser, J. A. J. Burgess, D. C. Fortin, W. K. Hiebert, and M. R. Freeman

J. Appl. Phys. 109, 07D309 (2011); http://dx.doi.org/10.1063/1.3540643 (6 pages) | Cited 3 times

Online Publication Date: 22 March 2011

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Micromechanical resonators are very useful for detection of magnetic torque. We have developed nanoscale torsional resonators fabricated within silicon nitride membranes, as a platform for magnetometry of nanoscale magnetic elements. We describe the rotational magnetic hysteresis of a 10 nm thick film deposited on a resonator, and a study of magnetic hysteresis in a single, 1 μm diameter permalloy disk. The torsional resonator is patterned using a dual beam scanning electron/focused ion system. For the 1 μm diameter disk, it is found to be possible to tune the conditions such that an apparent magnetic supercooling of vortex nucleation is observed, as would be suggested by the modified Landau theory of the C- to vortex-state switch as a first-order phase transition. Complementary transmission electron and Lorentz microscopy of the same structures have also been performed.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Vortex-antivortex creation and annihilation on CoFeB crosstie patterns

R. D. Gomez, J. S. Ma, A. Arkilic, S. H. Chung, and C. Krafft

J. Appl. Phys. 109, 07D310 (2011); http://dx.doi.org/10.1063/1.3536342 (3 pages) | Cited 1 time

Online Publication Date: 23 March 2011

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multimedia

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The creation and annihilation of vortex and antivortex pairs in crosstie walls on CoFeB islands were investigated using magnetic force microscopy (MFM) in the presence of applied field. The first vortex-antivortex pair (V-AV) is nucleated in a 4-domain Landau pattern from a section of a 180° degree Néel wall as a consequence of the formation of an end domain closure pattern. The V-AV pair creation satisfies the condition for the closure domain vortices to have the same chiralities. Pair annihilation occurs in two steps: a rapid advance of the vortices toward the more or less fixed antivortices followed by a deceleration caused by the decrease in local susceptibility. There is a spread in the annihilation fields that does not depend upon the core polarity but is determined by energy minimization.
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75.60.Ch Domain walls and domain structure
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities

Bulk and edge modes in two-dimensional magnonic crystal slab

J. W. Kłos, M. Krawczyk, and Mykhaylo Sokolovskyy

J. Appl. Phys. 109, 07D311 (2011); http://dx.doi.org/10.1063/1.3536534 (3 pages) | Cited 7 times

Online Publication Date: 23 March 2011

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Magnonic crystals are novel materials that open a new field to explore in the domain of spin dynamics in nanoscale systems. They also hold great promise for technological applications. The bulk, matrix, and edge magnonic states in a slab of two-dimensional magnonic crystal in the form of a superlattice of arrays of cylindrical dots of finite thickness are considered. The presented calculations are based on the plane wave method reformulated to gain in generality and efficiency, with both the exchange and the demagnetizing fields taken into account. The analytical formulas for Fourier coefficients of position-dependent material parameters for finite arrays of rods of various cross-sectional geometry and arrangement in the unit cell have been derived and presented. The localization properties of the edge modes found result from the magnonic spectrum and not from the nonuniformity of the internal magnetic field.
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75.30.Ds Spin waves
75.70.Rf Surface magnetism
75.60.-d Domain effects, magnetization curves, and hysteresis

Landau–Lifshitz magnetization dynamics driven by a random jump-noise process (invited)

I. Mayergoyz, G. Bertotti, and C. Serpico

J. Appl. Phys. 109, 07D312 (2011); http://dx.doi.org/10.1063/1.3536657 (6 pages) | Cited 3 times

Online Publication Date: 23 March 2011

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In the paper, a jump-noise process is introduced in magnetization dynamics equations in order to account for random thermal effects. It is demonstrated that in the case of small noise, Landau–Lifshitz and Gilbert damping terms emerge as average effects caused by the jump-noise process. This approach leads to simple formulas for the damping constant in terms of the scattering rate of the jump-noise process. These formulas also reveal the dependence of the damping constant on magnetization. The analysis of random switching of magnetization caused by the jump-noise process is presented. It is shown that the switching rate at very low temperatures may appreciably deviate from the predictions of thermal activation theory, which is consistent with experimental observations of low temperature switchings and is usually attributed to the phenomenon of “macroscopic tunneling” of magnetization.
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75.78.-n Magnetization dynamics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
05.40.Ca Noise
71.70.Di Landau levels
72.70.+m Noise processes and phenomena
75.30.Et Exchange and superexchange interactions

Nanoscale confined mode ferromagnetic resonance imaging of an individual Ni81Fe19 disk using magnetic resonance force microscopy (invited)

Inhee Lee, Yuri Obukhov, A. J. Hauser, F. Y. Yang, Denis V. Pelekhov, and P. Chris Hammel

J. Appl. Phys. 109, 07D313 (2011); http://dx.doi.org/10.1063/1.3536821 (5 pages) | Cited 4 times

Online Publication Date: 24 March 2011

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We demonstrate and characterize the localized Ferromagnetic Resonance (FMR) modes created in an individual micron-sized Ni81Fe19 disk by means of a strong inhomogeneous probe field applied anti-parallel to the saturated magnetization of the sample. Our variational calculation accurately predicts the frequencies of the localized modes in FMR spectra, and characterizes the sizes and all related internal magnetic fields of the Bessel function modes in a simple model analogous to particle wavefunctions in a quantum well. The localized modes enable FMR imaging of the nonuniform demagnetizing field inside a Py disk demonstrating a novel magnetic resonance imaging technique able to map internal fields in ferromagnets with spectroscopic accuracy.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
63.20.Pw Localized modes

Nucleation of vortex pairs in exchange biased nanoelements

A. S. M. Silva, Ana L. Dantas, G. O. G. Rebouças, and A. S. Carriço

J. Appl. Phys. 109, 07D314 (2011); http://dx.doi.org/10.1063/1.3537924 (3 pages) | Cited 3 times

Online Publication Date: 24 March 2011

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We report a theoretical investigation of interface effects in the magnetic order of interface biased iron and Permalloy™ elliptical nano-elements. Contrary to intuition, there is a partial pinning of the interface layer, favoring double vortex states along the hysteresis loop. Interface biasing affects the relative chirality and the distance of the vortices. Unbiased nanoelements may nucleate vortex pairs with the same chirality separated by an antivortex. For interface biased nanoelements the vortex pair forms with opposite chirality separated by a magnetic domain.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Fk Domain structures in nanoparticles
75.30.Et Exchange and superexchange interactions

Formation of magnetic domains and domain walls in epitaxial Fe3O4(100) elements (invited)

M. Fonin, C. Hartung, U. Rüdiger, D. Backes, L. Heyderman, F. Nolting, A. Fraile Rodríguez, and M. Kläui

J. Appl. Phys. 109, 07D315 (2011); http://dx.doi.org/10.1063/1.3540678 (4 pages) | Cited 3 times

Online Publication Date: 24 March 2011

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Magnetic domains and domain walls in epitaxial Fe3O4(100) elements (rings and wires) are imaged using magnetic force microscopy and photoemission electron microscopy. We show that the interplay between the four-fold magnetocrystalline anisotropy and the shape determines the equilibrium domain structure. Domain walls with a characteristic zig-zag structure are observed in Fe3O4(100) elements initially magnetized along one of the magnetocrystalline hard axes. We attribute the formation of zig-zag domain walls to the competition of the four-fold magnetocrystalline anisotropy, the exchange and dipolar coupling. A direct correlation between the wire width and the spin structure of zig-zag domain walls is found.
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75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Nonlocal ultrafast magnetization dynamics in the high fluence limit

K. C. Kuiper, G. Malinowski, F. Dalla Longa, and B. Koopmans

J. Appl. Phys. 109, 07D316 (2011); http://dx.doi.org/10.1063/1.3540681 (3 pages)

Online Publication Date: 25 March 2011

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In order to explain a number of recent experimental observations of laser-induced femtosecond demagnetization in the large fluence limit, we discuss the consequences of a recently proposed nonlocal approach. A microscopic description of spin flip scattering is implemented in an effective three temperature model, including electronic heat diffusion. Effects of finite film thickness on the demagnetization transients are discussed. Our results show a clear saturation of the ultrafast demagnetization, in excellent agreement with experimental observations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
78.47.J- Ultrafast spectroscopy (<1 psec)

Comparison of electrical techniques for magnetization dynamics measurements in micro/nanoscale structures

Sang-Hyun Lim, T. M. Wallis, Atif Imtiaz, Dazhen Gu, Pavol Krivosik, and Pavel Kabos

J. Appl. Phys. 109, 07D317 (2011); http://dx.doi.org/10.1063/1.3544480 (3 pages) | Cited 1 time

Online Publication Date: 25 March 2011

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Three all-electrical detection techniques—differential resistance (dV/dI), rf/microwave transmission, and spin rectification measurements—were used to measure the magnetic response of individual patterned Permalloy structures. The investigated techniques enable the identification of distinctive magnetization states, such as vortex nucleation and excitation, domain wall motion, ferromagnetic resonance, and spin wave excitations both in the quasistatic and dynamic regimes. The techniques differ in signal-to-noise ratio and sensitivity to the different types of magnetization responses studied here, suggesting that the use of multiple techniques can significantly improve the understanding of magnetically complex structures.
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75.78.Fg Dynamics of domain structures
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Ds Spin waves
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Optimum design consideration for interferometric spin wave logic operations

Y. Nakashima, K. Nagai, T. Tanaka, and K. Matsuyama

J. Appl. Phys. 109, 07D318 (2011); http://dx.doi.org/10.1063/1.3549438 (3 pages) | Cited 2 times

Online Publication Date: 25 March 2011

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In the present study, the operational modes and the structural design are optimized to realize potential performance in the interferometric spin wave logic circuits. Successive functional operations, such as generation, propagation, and inductive detection of spin wave packets are numerically studied by using micromagnetic simulations. The logic input is coded with the phase of pulsed microwave currents applied through the generators. Among the various kinds of the investigated spin wave (SW) modes, the backward volume mode exhibits superior performance. Various structural and operational parameters, including the pulsed microwave frequency and the film thickness of the magnetic strip, were optimized by taking the inductive output voltage (Vout) as a quantitative criterion. The several orders of difference obtained in the Vout for the different logic inputs demonstrates the successful exclusive-not-OR operation.
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75.30.Ds Spin waves
75.78.Cd Micromagnetic simulations
72.25.-b Spin polarized transport
75.76.+j Spin transport effects

Partial band gaps in magnonic crystals

C. H. O. Costa, M. S. Vasconcelos, and E. L. Albuquerque

J. Appl. Phys. 109, 07D319 (2011); http://dx.doi.org/10.1063/1.3549557 (3 pages) | Cited 1 time

Online Publication Date: 28 March 2011

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In this work we investigate magnonic band gaps, in the THz frequency range, in periodic and quasiperiodic (Fibonacci sequence) magnonic crystals formed by layers of cobalt and permalloy. Our theoretical model is based on a magnetic Heisenberg Hamiltonian in the exchange regime, together with a transfer-matrix treatment within the random-phase approximation. For periodic arrangements, the bulk band structure is analogous to those found in photonic crystals, while for quasiperiodic multilayers it presents additional pass bands similar to those found in photonic crystals with defects.
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73.21.Ac Multilayers
73.20.At Surface states, band structure, electron density of states
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.10.Jm Quantized spin models, including quantum spin frustration

An approach for analysis of magnetostatic volume waves in magnonic crystals

Kai H. Chi, Yun Zhu, Rong W. Mao, James P. Dolas, and Chen S. Tsai

J. Appl. Phys. 109, 07D320 (2011); http://dx.doi.org/10.1063/1.3549559 (3 pages) | Cited 1 time

Online Publication Date: 28 March 2011

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A theoretical approach, based on Walker’s equation, to analyze the propagation characteristics of magnetostatic volume waves in magnonic crystals with periodic variation in magnetic layer thickness is presented. The properties of bandgaps versus the thickness parameters of the magnetic layer and the magnetically tuned bandgaps are verified experimentally.
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75.30.Ds Spin waves

An evolutionary computation approach for time-harmonic field problems involving nonlinear magnetic media

A. A. Adly and S. K. Abd-El-Hafiz

J. Appl. Phys. 109, 07D321 (2011); http://dx.doi.org/10.1063/1.3549606 (3 pages)

Online Publication Date: 28 March 2011

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Recently, the particle swarm optimization evolutionary approach has been successfully utilized in field computation for devices involving nonlinear magnetic media. The purpose of this paper is to extend the aforementioned approach toward the solution of time-harmonic field problems. More specifically, unknown time-step vector magnetic potentials leading to the minimization of the energy functional are computed in an evolutionary mechanism to determine instantaneous field components. The proposed approach has been implemented and utilized for different supply frequencies, field amplitudes, and media characteristics. Details of the approach as well as comparisons with finite-element computations demonstrating the accuracy of the approach are given in the paper.
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02.60.Pn Numerical optimization
02.70.Dh Finite-element and Galerkin methods
75.40.Mg Numerical simulation studies

Extrinsic damping contribution in soft magnetic thin films detected by permeability spectra

Feng Xu, Shandong Li, and C. K. Ong

J. Appl. Phys. 109, 07D322 (2011); http://dx.doi.org/10.1063/1.3549611 (3 pages) | Cited 3 times

Online Publication Date: 28 March 2011

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This work focuses on the identification of extrinsic damping contribution in FeCoN and FeCoSiN soft magnetic thin films by microwave permeability spectra measurements. The comparison of hysteresis loops shows that FeCoSiN thin film has a stronger in-plane uniaxial anisotropy. Through the analysis on the field-dependent frequency linewidth, the extrinsic damping contribution from two-magnon-scattering in FeCoN thin films is identified. The two-magnon-scattering damping contribution is greatly enhanced in FeCoSiN film due to the granular microstructure which brings about much more interface area between the two phases.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
78.70.Gq Microwave and radio-frequency interactions
61.72.-y Defects and impurities in crystals; microstructure
75.30.Ds Spin waves

Theory of dipole-exchange spin waves in metallic ferromagnetic nanotubes of large aspect ratio

Tushar K. Das and Michael G. Cottam

J. Appl. Phys. 109, 07D323 (2011); http://dx.doi.org/10.1063/1.3554208 (3 pages)

Online Publication Date: 28 March 2011

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A macroscopic continuum theory is presented for the dipole-exchange spin waves in nanometer-sized cylindrical tubes with a large length-to-diameter aspect ratio. The magnetization and applied magnetic field are taken parallel to the cylinder axis, and the properties of the hybridized surface and bulk magnetic excitations are studied in relation to the inner and outer interfaces of the nanotubes. The calculations describe the radial and angular quantization of the different modes for both unpinned and effective pinned cases. The results for tube geometries are found to be in contrast with the limiting (single-interface) special cases of wires and antiwires. Numerical examples are presented mainly for Ni materials.
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75.75.-c Magnetic properties of nanostructures
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Et Exchange and superexchange interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys

Static and dynamic magnetic properties of epitaxial Co2FeAl Heusler alloy thin films

G. Ortiz, M. S. Gabor, T. Petrisor, Jr., F. Boust, F. Issac, C. Tiusan, M. Hehn, and J. F. Bobo

J. Appl. Phys. 109, 07D324 (2011); http://dx.doi.org/10.1063/1.3549581 (3 pages) | Cited 2 times

Online Publication Date: 30 March 2011

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Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600 °C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010 ± 30 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032 ± 40 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 × 10−3, and a minimum value of 3.8 × 10−3 for the Cr buffered one.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Challenges toward gigabit-scale spin-transfer torque random access memory and beyond for normally off, green information technology infrastructure (Invited)

Takayuki Kawahara

J. Appl. Phys. 109, 07D325 (2011); http://dx.doi.org/10.1063/1.3556681 (6 pages) | Cited 1 time

Online Publication Date: 30 March 2011

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Show Abstract
If spin-transfer torque RAM (SPRAM) technology is used as a true nonvolatile RAM, it will be able to provide normally “off” and instant “on” functions. This would drastically reduce the power consumption of information technology (IT) equipment and its infrastructure while preserving high performance, thus leading to a green IT infrastructure. This paper describes the design issues and solutions for creating a Gb-scale SPRAM; scaling in memory cell current (∝F, F: feature size) and the tunneling magnetoresistive (TMR) device’s write current (∝F2), the maximum voltage applicable to a TMR device (TMR ratio and resistance area product are considered); and the thermal stability of the TMR device (depending on the operation mode and density). Moreover, the cell and array configurations and an indispensable disruptive reading operation are shown for 4F2DDRx compatible operations. SPRAM can cover a system composed of a DRAM region. Finally, the potential of a multibit memory structure that covers the area of a not-and flash memory is discussed.
Show PACS
84.30.Sk Pulse and digital circuits
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
68.60.Dv Thermal stability; thermal effects
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