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17 Dec 2012

Volume 101, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 101, 251102 (2012); http://dx.doi.org/10.1063/1.4770503 (4 pages)

Haider Butt, Tim Butler, Yunuen Montelongo, Ranjith Rajesekharan, Timothy D. Wilkinson, and Gehan A. J. Amaratunga
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Charge density wave excitations in stripe-type charge ordered Pr0.5Sr0.5MnO3 manganite

Rakesh Rana, D. S. Rana, K. R. Mavani, I. Kawayama, H. Murakami, and M. Tonouchi

Appl. Phys. Lett. 101, 252401 (2012); http://dx.doi.org/10.1063/1.4772474 (4 pages)

Online Publication Date: 17 December 2012

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We show that a charge-density wave mode submerged in large conductivity of the stripe-type charge-ordered (CO) crystal of Pr0.5Sr0.5MnO3 (PSMO) can be extracted by exciting selective crystallographic planes using polarized terahertz field. Low energy (1–7 meV) dynamics have been explored in the (100), (110), and (111) epitaxial films of PSMO manganite. Of (110) and (111) films representing bulk-like CO, the former exhibits a peak in the conductivity-energy spectrum with attributes of charge-density wave mode along a specific in-plane axis. On the contrary, the CO (111) and the phase-separated (100) films lack this low energy mode but exhibit a Drude-like spectral behavior in the metallic regime. These studies reveal a variety in isothermal charge dynamics originating from the anisotropic nature of the stripe charge-order.
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75.30.Ds Spin waves
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.78.-n Magnetization dynamics
73.61.Ng Insulators

Dynamics of the vortex core in magnetic nanodisks with a ring of magnetic impurities

D. Toscano, S. A. Leonel, P. Z. Coura, F. Sato, R. A. Dias, and B. V. Costa

Appl. Phys. Lett. 101, 252402 (2012); http://dx.doi.org/10.1063/1.4772071 (4 pages)

Online Publication Date: 17 December 2012

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In this work, we used numerical simulations to study the effect of a ring of magnetic impurities on the vortex core dynamics in nanodisks of Permalloy. The presence of the ring not only allowed us to modulate the gyrotropic frequency but also provided us a way to confine the vortex core. We observed that the gyrotropic frequency depends on the ring parameters. Moreover, we have noticed that the switching of the vortex core polarity can be obtained from the vortex core-impurity interaction under peculiar conditions, in particular, when the ring works for pinning the vortex core.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.40.Mg Numerical simulation studies
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.30.Hx Magnetic impurity interactions

Promotion of [001]-oriented L10-FePt by rapid thermal annealing with light absorption layer

Liang-Wei Wang, Wen-Chieh Shih, Yun-Chung Wu, and Chih-Huang Lai

Appl. Phys. Lett. 101, 252403 (2012); http://dx.doi.org/10.1063/1.4772072 (4 pages) | Cited 2 times

Online Publication Date: 17 December 2012

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Highly [001]-oriented L10-FePt grown on SiO2‖Si is achieved by using rapid thermal annealing (RTA) at 400 °C. Due to the dramatic divergence of light absorption ability between Si and FePt films, Si behaves as the light absorption layer to absorb more light emitted from RTA system, which gives rise to larger thermal expansion on Si and induces in-plane tensile stress on FePt films. By raising heating rate during RTA, the transient light intensity is increased; therefore, higher in-plane tensile stress on FePt films is generated, which effectively suppresses the opening-up of in-plane hysteresis loops.
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65.40.De Thermal expansion; thermomechanical effects
61.72.Cc Kinetics of defect formation and annealing

Temperature dependence of spin lifetime of conduction electrons in bulk germanium

Chinkhanlun Guite and V. Venkataraman

Appl. Phys. Lett. 101, 252404 (2012); http://dx.doi.org/10.1063/1.4772500 (3 pages) | Cited 2 times

Online Publication Date: 18 December 2012

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Optically generated spin polarized electrons in bulk n-type Ge samples have been detected by using a radio-frequency modulation technique. Using the Hanle effect in an external magnetic field, the spin lifetime was measured as a function of temperature in the range 90 K to 180 K. The lifetime decreases with increasing temperature from ∼ 5 ns at 100 K to ∼ 2 ns at 180 K. We show that the temperature dependence is consistent with the Elliott-Yafet spin relaxation mechanism [R. J. Elliot, Phys. Rev. 96, 266 (1954)].
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72.25.Dc Spin polarized transport in semiconductors
72.25.Rb Spin relaxation and scattering
72.80.Cw Elemental semiconductors
78.20.Jq Electro-optical effects
81.05.Cy Elemental semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Origin of magnetic anisotropy in ZnO/CoFe2O4 and CoO/CoFe2O4 core/shell nanoparticle systems

Elin L. Winkler, Enio Lima, Jr., Dina Tobia, Martín E. Saleta, Horacio E. Troiani, Elisabetta Agostinelli, Dino Fiorani, and Roberto D. Zysler

Appl. Phys. Lett. 101, 252405 (2012); http://dx.doi.org/10.1063/1.4771993 (4 pages) | Cited 1 time

Online Publication Date: 18 December 2012

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ZnO-core/CoFe2O4-shell nanoparticles of 7.4 nm average size have been synthesized and their magnetic properties have been compared to those of CoO-core/CoFe2O4-shell nanoparticles with similar morphology. The coercive field values are much lower than those for CoO/CoFe2O4 nanoparticles (e.g., at 5 K: Hc = 7.8 kOe for ZnO/CoFe2O4; Hc = 27.8 kOe for CoO/CoFe2O4). The nature of the coercive field values is explained by a phenomenological model for the free energy of a non-magnetic core, or an antiferromagnetic core, encapsulated by a hard ferrimagnetic shell.
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75.75.Cd Fabrication of magnetic nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Mapping microwave field distributions via the spin Hall effect

Vincent Vlaminck, Helmut Schultheiss, John E. Pearson, Frank Y. Fradin, Sam D. Bader, and Axel Hoffmann

Appl. Phys. Lett. 101, 252406 (2012); http://dx.doi.org/10.1063/1.4772635 (4 pages) | Cited 1 time

Online Publication Date: 18 December 2012

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The spatial variation of the spin pumping–inverse spin Hall effect was studied in a palladium/permalloy bilayer via a coplanar waveguide ferromagnetic resonance (CPW-FMR) broadband technique. The inverse spin Hall signal is both inhomogeneous and asymmetric with respect to both the position along the CPW and the excitation port. Based on this observation, we show how the inverse spin Hall effect can be used as a sensitive probe for mapping the microwave magnetic field distribution in the FMR frequency range.
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72.25.Mk Spin transport through interfaces
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Magnetic switching driven by nanosecond scale heat and magnetic field pulses: An application of macrospin Landau-Lifshitz-Bloch model

U. Kilic, G. Finocchio, T. Hauet, S. H. Florez, G. Aktas, and O. Ozatay

Appl. Phys. Lett. 101, 252407 (2012); http://dx.doi.org/10.1063/1.4772486 (5 pages) | Cited 2 times

Online Publication Date: 19 December 2012

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High-temperature (near Curie-point) magnetization-behavior in materials with strong-perpendicular-magnetocrystalline-anisotropy has recently gained importance due to potential applications in thermally/heat-assisted-magnetic-recording (TAR/HAMR) systems. We have implemented a macrospin-model within the Landau-Lifshitz-Bloch formalism for strongly exchange-coupled CoNi/Pd multilayers subject to nanosecond-scale localized-heat and magnetic-field pulses. The temperature dependence of the longitudinal-susceptibility, as determined from a single-fitting-parameter of the experimental coercive-field, is consistent with the previously reported ab initio calculations. We demonstrate that this model is able to predict the full map of switching-speed as a function of magnetic-field and local-temperature providing a robust tool for the evaluation of this and similar material systems in TAR/HAMR applications.
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75.78.Jp Ultrafast magnetization dynamics and switching
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Extensive study of giant magnetoresistance properties in half-metallic Co2(Fe,Mn)Si-based devices

Y. Sakuraba, M. Ueda, Y. Miura, K. Sato, S. Bosu, K. Saito, M. Shirai, T. J. Konno, and K. Takanashi

Appl. Phys. Lett. 101, 252408 (2012); http://dx.doi.org/10.1063/1.4772546 (4 pages) | Cited 2 times

Online Publication Date: 19 December 2012

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Fully epitaxial Co2FexMn1−xSi(CFMS)/Ag/Co2FexMn1−xSi current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses tCFMS were prepared. The highest magnetoresistance (MR) ratios, 58% at room temperature and 184% at 30 K, were observed in the sample with x = 0.4 and tCFMS = 3 nm. Enhancement of interface spin-asymmetry was suggested for x = 0.4 compared with that at x = 0. A MR ratio of 58% was also observed even in a very thin trilayer structure, CFMS(4 nm)/Ag(3 nm)/CFMS(2 nm), which is promising for a next-generation magnetic read sensor for high-density hard disk drives.
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75.47.De Giant magnetoresistance
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.75.Ss Magnetic field sensors using spin polarized transport
72.25.Dc Spin polarized transport in semiconductors

Deviation from exponential decay for spin waves excited with a coplanar waveguide antenna

Daniel R. Birt, Kyongmo An, Maxim Tsoi, Shingo Tamaru, David Ricketts, Kin L. Wong, Pedram Khalili Amiri, Kang L. Wang, and Xiaoqin Li

Appl. Phys. Lett. 101, 252409 (2012); http://dx.doi.org/10.1063/1.4772798 (4 pages)

Online Publication Date: 20 December 2012

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We have investigated the propagation of surface spin waves in a Permalloy thin film excited by an asymmetric coplanar antenna. A surprising oscillatory behavior superimposed on the exponential decay is observed in the spin wave intensity mapped with the micro-Brillouin light scattering technique. The oscillations can be modeled as the interference between a propagating spin wave and a background magnetization with spatially uniform phase. We use a simple closed-form equation that includes both contributions to fit our experimental results. From the fit results, we extract the spin wave propagation length and the spin wave vector in a frequency range limited by the antenna bandwidth.
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84.40.Ba Antennas: theory, components and accessories

Electron effective mass in n-type electron-induced ferromagnetic semiconductor (In,Fe)As: Evidence of conduction band transport

Pham Nam Hai, Le Duc Anh, and Masaaki Tanaka

Appl. Phys. Lett. 101, 252410 (2012); http://dx.doi.org/10.1063/1.4772630 (5 pages)

Online Publication Date: 20 December 2012

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The electron effective mass (m*) in n-type carrier-induced ferromagnetic semiconductor (In,Fe)As was estimated by using the thermoelectric Seebeck effect. It was found that m* is 0.03 ∼ 0.17m0 depending on the electron concentration, where m0 is the free electron mass. These values are similar to those of electrons in the conduction band of n+ InAs. The Fermi level EF in (In,Fe)As is located at least 0.15 eV above the conduction band bottom. Our results indicate that electron carriers in (In,Fe)As reside in the conduction band, rather than in a hypothetical Fe-related itinerant impurity band.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Ey III-V and II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
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Non-volatile spin switch for Boolean and non-Boolean logic

Supriyo Datta, Sayeef Salahuddin, and Behtash Behin-Aein

Appl. Phys. Lett. 101, 252411 (2012); http://dx.doi.org/10.1063/1.4769989 (5 pages)

Online Publication Date: 20 December 2012

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We show that the established physics of spin valves together with the recently discovered giant spin-Hall effect could be used to construct Read and Write units that can be integrated into a single spin switch with input-output isolation, gain and fan-out similar to complementary metal oxide semiconductor inverters, but with the information stored in nanomagnets making it non-volatile. Such spin switches could be interconnected, with no external amplification, just with passive circuit elements, to perform logic operations. Moreover, since the digitization and storage occur naturally in the magnets, the voltages can be used to implement analog “weighting” for non-Boolean logic.
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84.30.Sk Pulse and digital circuits
85.70.-w Magnetic devices

Mechanism of reversing the Neel domain walls in the Co nanostripes with transverse magnetic anisotropy

A. V. Davydenko, A. V. Ognev, E. V. Pustovalov, and L. A. Chebotkevich

Appl. Phys. Lett. 101, 252412 (2012); http://dx.doi.org/10.1063/1.4772981 (4 pages)

Online Publication Date: 21 December 2012

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We present a model of reversing the Neel domain walls (DWs) in the laminar domain structure of epitaxial Co(111) nanostripes. The laminar domain structure in nanostripes is induced by magnetic anisotropy, the easy axis of which is orthogonal to the long axis and lies in the plane of the stripes. Magnetization reversal in the DWs occurs by nucleation of vortices at the opposite ends of adjacent DWs and their subsequent propagation along the domain DWs. Vortices in adjacent DWs have opposite chirality. The out of plane component of the magnetization in the vortices cores is confirmed by micromagnetic modeling.
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75.75.Fk Domain structures in nanoparticles
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Magnetic power inverter: AC voltage generation from DC magnetic fields

Jun'ichi Ieda and Sadamichi Maekawa

Appl. Phys. Lett. 101, 252413 (2012); http://dx.doi.org/10.1063/1.4773214 (4 pages)

Online Publication Date: 21 December 2012

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We propose a method that allows power conversion from DC magnetic fields to AC electric voltages using domain wall (DW) motion in ferromagnetic nanowires. The device concept relies on spinmotive force, voltage generation due to magnetization dynamics. Sinusoidal modulation of the nanowire width introduces a periodic potential for a DW, the gradient of which exerts variable pressure on the traveling DW. This results in time variation of the DW precession frequency and the associated voltage. Using a one-dimensional model, we show that the frequency and amplitude of the AC outputs can be tuned by the DC magnetic fields and wire-design.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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