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21 Mar 2011

Volume 98, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 98, 123101 (2011); http://dx.doi.org/10.1063/1.3567492 (3 pages)

Linus C. Chuang, Michael Moewe, Kar Wei Ng, Thai-Truong D. Tran, Shanna Crankshaw, Roger Chen, Wai Son Ko, and Connie Chang-Hasnain
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Understanding the role played by Fe on the tuning of magnetocaloric effect in Tb5Si2Ge2

A. M. Pereira, A. M. dos Santos, C. Magen, J. B. Sousa, P. A. Algarabel, Y. Ren, C. Ritter, L. Morellon, M. R. Ibarra, and J. P. Araújo

Appl. Phys. Lett. 98, 122501 (2011); http://dx.doi.org/10.1063/1.3567920 (3 pages) | Cited 5 times

Online Publication Date: 21 March 2011

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In this letter, it is shown that when replacing Ge by Fe in Tb5Si2Ge2 the structural transition still occurs and enhances the magnetocaloric effect (MCE) (up to 66%) with maximum of MCE at a critical Fe amount where the magnetic and structural transitions become fully coupled. It is observed that Fe concentration is able to mimic the effect of external pressure as it induces a complex microstructure, that tunes long range strain fields. This knowledge is crucial for the development of strategies toward materials with improved performance for efficient magnetic refrigeration applications.
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75.30.Sg Magnetocaloric effect, magnetic cooling
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Tunneling magnetoresistance in epitaxial discontinuous Fe/MgO multilayers

A. García-García, J. A. Pardo, P. Štrichovanec, C. Magén, A. Vovk, J. M. De Teresa, G. N. Kakazei, Y. G. Pogorelov, L. Morellón, P. A. Algarabel, and M. R. Ibarra

Appl. Phys. Lett. 98, 122502 (2011); http://dx.doi.org/10.1063/1.3569149 (3 pages) | Cited 2 times

Online Publication Date: 21 March 2011

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Epitaxial discontinuous Fe/MgO multilayers have been grown by pulsed laser deposition on MgO(001) single-crystal substrates. The multilayers with 0.6 nm nominal Fe layers thickness are superparamagnetic and demonstrate tunneling magnetoresistance (TMR) in the current-in-plane configuration. Increasing deposition temperature causes an improvement in crystal quality and is accompanied by higher TMR ratios. The maximum value (9.2% TMR at room temperature and 18 kOe magnetic field) trebles that of polycrystalline samples deposited simultaneously on glass substrates. A model formula for TMR ratio that includes both spin-dependent tunneling and spin-filtering effect is proposed to explain these results.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
81.15.Fg Pulsed laser ablation deposition
68.65.Ac Multilayers
75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Evolution of itinerant ferromagnetism in SrxPb1−xRuO3 (0 ≤ x ≤ 1): Interplay between Jahn–Teller distortion and A-site disorder

Hai-Shuang Lu and Sheng Ju

Appl. Phys. Lett. 98, 122503 (2011); http://dx.doi.org/10.1063/1.3567536 (3 pages)

Online Publication Date: 22 March 2011

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Density functional theory with local spin density approximation is applied to study the evolution of ferromagnetism in SrxPb1−xRuO3 (0 ≤ x ≤ 1). Besides the enhanced Pb–O covalence and Pb–Ru hybridization, the Jahn–Teller effect, which favors the low-spin state (S = 0) of Ru4+ in a stretched oxygen octahedra, is found to be the origin of the observed paramagnetism in PbRuO3. With the introduction of Sr, the Pb–Ru hybridization is weakened and an intermediate-spin state (S = 1) is preferred via the opposite Jahn–Teller effect in a compressed oxygen octahedra, leading to the appearance of ferromagnetism for x>0.5. Our calculations provide a good explanation of recent experimental findings.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.10.Lp Band and itinerant models
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials

Spreading sequences for fast switching process in spin-valve nanopillars

Mario Carpentieri, Marco Ricci, Pietro Burrascano, and Luis Torres

Appl. Phys. Lett. 98, 122504 (2011); http://dx.doi.org/10.1063/1.3569947 (3 pages) | Cited 1 time

Online Publication Date: 22 March 2011

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A detailed study of the effects of binary spreading sequences (BSS) excitation in the magnetization dynamics of exchange-biased spin-valves driven by spin-transfer-torque has been carried out by full micromagnetic modeling. We show that the use of BSS allows to trigger the magnetization reversal by exciting its main precession modes. We compared our numerical results with the experimental ones reported by [ Cui et al., Phys. Rev. B 77, 214440 (2008)] , attaining quantitative agreement. Advantages of BSS as microwave source with respect to a sinusoidal signal are also reported and discussed.
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75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.30.Et Exchange and superexchange interactions

Momentum transfer resolved memory in a magnetic system with perpendicular anisotropy

Keoki A. Seu, S. Roy, R. Su, D. H. Parks, E. Shipton, E. E. Fullerton, and S. D. Kevan

Appl. Phys. Lett. 98, 122505 (2011); http://dx.doi.org/10.1063/1.3569952 (3 pages)

Online Publication Date: 23 March 2011

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We have used resonant, coherent soft x-ray scattering to measure wave vector resolved magnetic domain memory in Co/Pd multilayers. The technique uses angular cross correlation functions and can be applied to any system with circular annuli of constant values of scattering wave vector q. In our Co/Pd film, the memory exhibits a maximum at q = 0.0384 nm−1 near initial reversal that decreases in magnitude as the magnetization is further reversed. The peak is attributed to bubble domains that nucleate reproducibly near initial reversal and which grow into a labyrinth domain structure that is not reproduced from one magnetization cycle to the next.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.70.Ck X-ray scattering
68.65.Ac Multilayers
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Gw Magnetic anisotropy

Excitation of propagating spin waves with global uniform microwave fields

Y. Au, T. Davison, E. Ahmad, P. S. Keatley, R. J. Hicken, and V. V. Kruglyak

Appl. Phys. Lett. 98, 122506 (2011); http://dx.doi.org/10.1063/1.3571444 (3 pages) | Cited 11 times

Online Publication Date: 24 March 2011

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We demonstrate a magnonic architecture that converts global free-space uniform microwaves into spin waves propagating in a stripe magnonic waveguide. The architecture is based upon dispersion mismatch between the narrow magnonic waveguide and a wide “antenna” patch, both patterned from the same magnetic film. The spin waves injected into the waveguide travel to distances as large as several tens of micrometers. The antennas can be placed at multiple positions on a magnonic chip and used to excite mutually coherent multiple spin waves for magnonic logic operations. This demonstration paves way for “magnonics” to become a pervasive technology for information processing.
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75.30.Ds Spin waves
75.70.Ak Magnetic properties of monolayers and thin films

Torque approach for tuning exchange bias training effect in polycrystalline NiFe/FeMn bilayers

Z. Shi, J. Du, R. W. Chantrell, S. Mangin, and S. M. Zhou

Appl. Phys. Lett. 98, 122507 (2011); http://dx.doi.org/10.1063/1.3569140 (3 pages) | Cited 4 times

Online Publication Date: 25 March 2011

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In order to tune the exchange bias training effect, a torque approach is proposed. Torque loops are performed between two consecutive hysteresis loops by clockwise and counterclockwise rotation of the sample within an angular range under an in-plane external magnetic field. For the angular range from 0° to 180°, the coercivity HC and the exchange field HE are both reduced and the pinning direction (PD) orientation is changed, exhibiting the first type training effect. For the angular range from −20° to 380°, HC and the PD orientation are almost unchanged although HE is reduced, exhibiting the second type training effect.
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75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
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