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26 Sep 2011

Volume 99, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 99, 131101 (2011); http://dx.doi.org/10.1063/1.3641907 (3 pages)

Linas Minkevičius, Vincas Tamošiūnas, Irmantas Kašalynas, Dalius Seliuta, Gintaras Valušis, Alvydas Lisauskas, Sebastian Boppel, Hartmut G. Roskos, and Klaus Köhler
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Magnetic anisotropy of FePt: Effect of lattice distortion and chemical disorder

C. J. Aas, L. Szunyogh, J. S. Chen, and R. W. Chantrell

Appl. Phys. Lett. 99, 132501 (2011); http://dx.doi.org/10.1063/1.3644478 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2011

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We perform first principles calculations of the magnetocrystalline anisotropy energy (MAE) in the five samples of L10 FePt that were studied experimentally by Ding and co-workers [J. Appl. Phys. 97, 10H303 (2005)]. The effect of temperature-induced spin fluctuations is estimated by scaling the MAE down according to previous Langevin dynamics simulations. Including chemical disorder as given in experiment, the experimental correlation between the MAE and the lattice mismatch is qualitatively well reproduced. Moreover, we determine the chemical order parameters that reproduce exactly the experimental MAE of each of the samples. Our observations lead to the conclusion that the MAE of the FePt samples is determined by the chemical disorder rather than by lattice distortion.
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75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.30.Ds Spin waves

Spin-transfer-torque reversal in perpendicular anisotropy spin valves with composite free layers

I. Yulaev, M. V. Lubarda, S. Mangin, V. Lomakin, and Eric E. Fullerton

Appl. Phys. Lett. 99, 132502 (2011); http://dx.doi.org/10.1063/1.3643046 (3 pages) | Cited 5 times

Online Publication Date: 26 September 2011

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We describe modeling of spin-transfer-torque (STT) driven reversal in nanopillars with strong out-of-plane magnetic anisotropy where the free layer is a magnetically hard-soft composite structure. By adjusting the exchange coupling between the hard and soft layers, we observed reduced current amplitude and pulse durations required to reverse the magnetization compared to a homogeneous free layer of comparable thermal stability. The reduction in critical current comes from the increased STT efficiency acting on the soft layer. As such, the switching current is relatively insensitive to the damping parameter of the magnetic hard layer. These properties make composite free layers promising candidates for STT-based magnetic memories.
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75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Dynamic and temperature effects in microwave assisted switching: Evidence of chaotic macrospin dynamics

Dorin Cimpoesu and Alexandru Stancu

Appl. Phys. Lett. 99, 132503 (2011); http://dx.doi.org/10.1063/1.3640230 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2011

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Microwave assisted switching (MAS) is a method that can be used in magnetic recording in order to reduce the writing field. In order to have a robust method, the factors influencing MAS have to be systematically analyzed. In this paper we use the stochastic Landau-Lifsitz-Gilbert simulations to examine MAS in terms of microwave amplitude and frequency, damping, and the parameters describing the pulse field. Also, we discuss about the troubling aspect of numerical induced chaos.
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75.50.Ss Magnetic recording materials
02.50.Ey Stochastic processes

Magnetic properties and magnetocaloric effects in R3Ni2 (R = Ho and Er) compounds

Q. Y. Dong, J. Chen, J. Shen, J. R. Sun, and B. G. Shen

Appl. Phys. Lett. 99, 132504 (2011); http://dx.doi.org/10.1063/1.3643142 (3 pages) | Cited 6 times

Online Publication Date: 26 September 2011

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Magnetic and magnetocaloric properties of R3Ni2 (R = Ho and Er) compounds have been investigated. Both Ho3Ni2 and Er3Ni2 compounds undergo two successive phase transitions: spin reorientation transition and second-order ferromagnetic-paramagnetic transition. The maximal values of magnetic entropy change are achieved to be 21.7 J kg−1 K−1 for Ho3Ni2 and 19.5 J kg−1 K−1 for Er3Ni2 for a field change of 0-5 T. A large refrigerant capacity (RC) of 496 J kg−1 in the composite material is also obtained. Large reversible magnetocaloric effect and RC indicate the potentiality of R3Ni2 (R = Ho and Er) compounds as candidates for low-temperature magnetic refrigerant.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Cc Other ferromagnetic metals and alloys
75.20.En Metals and alloys
75.30.Ds Spin waves
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Spin waves interference from rising and falling edges of electrical pulses

Jae Hyun Kwon, Sankha Subhra Mukherjee, Mahdi Jamali, Masamitsu Hayashi, and Hyunsoo Yang

Appl. Phys. Lett. 99, 132505 (2011); http://dx.doi.org/10.1063/1.3643156 (3 pages) | Cited 3 times

Online Publication Date: 26 September 2011

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The authors have investigated the effect of the electrical pulse width of input excitations on the generated spin waves in a NiFe strip using pulse inductive time domain measurements. The authors have shown that the spin waves resulting from the rising- and the falling-edges of input excitation pulses interfere either constructively or destructively and have provided conditions for obtaining spin wave packets with maximum intensity at different bias conditions.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Bb Fe and its alloys

Effective cancellation of residual magnetic interference induced from a shielded environment for precision magnetic measurements

Seong-Min Hwang, Kiwoong Kim, Chan Seok Kang, Seong-Joo Lee, and Yong-Ho Lee

Appl. Phys. Lett. 99, 132506 (2011); http://dx.doi.org/10.1063/1.3643427 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2011

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Using the method of inverse problem, we designed a cancellation coil that prevents a strong pulsed magnetic field inside a magnetically shielded room (MSR) from magnetizing and inducing large-scale eddy currents around the shielding materials. We implemented this coil with discrete current loops and evaluated it numerically and experimentally. Without the cancellation coil, the transient residual magnetic field in the middle of the MSR was greater than 0.1 μT for 63.5 ms, while the cancellation coil reduced it to less than 0.1 μT after 10.8 ms, shortening the decay time by 83.0%.
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41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Inter/intra granular exchange and thermal activation in nanoscale granular magnetic materials

C. Morrison, L. Saharan, G. Hrkac, T. Schrefl, Y. Ikeda, K. Takano, J. J. Miles, and T. Thomson

Appl. Phys. Lett. 99, 132507 (2011); http://dx.doi.org/10.1063/1.3644469 (3 pages) | Cited 2 times

Online Publication Date: 27 September 2011

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We explain the effect of inter/intra granular exchange coupling and thermal activation on the switching behavior of nano-scale granular magnetic materials. For an ideal, non-interacting granular system, the minimum switching field occurs at 45° from the easy axis of the grains. We show through simulation and measurements, using a CoCrPt oxide-segregated granular film as a model system, that there is a clear shift in the angle of applied field at which the minimum switching field occurs. This arises solely due to incoherent reversal induced by inter-granular exchange coupling or incoherency within larger grains, rather than thermal activation.
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75.30.Et Exchange and superexchange interactions
75.40.Mg Numerical simulation studies
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.78.Jp Ultrafast magnetization dynamics and switching

Ferromagnetism in ZnO co-doped with Mn and N studied by soft x-ray magnetic circular dichroism

T. Kataoka, Y. Yamazaki, V. R. Singh, Y. Sakamoto, A. Fujimori, Y. Takeda, T. Ohkochi, S.-I. Fujimori, T. Okane, Y. Saitoh, H. Yamagami, A. Tanaka, M. Kapilashrami, L. Belova, and K. V. Rao

Appl. Phys. Lett. 99, 132508 (2011); http://dx.doi.org/10.1063/1.3643044 (3 pages) | Cited 2 times

Online Publication Date: 27 September 2011

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We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2p → 3d XMCD results, it is shown that, while XMCD signals only due to paramagnetic Mn2+ ions were observed in ZnO:Mn, nonmagnetic, paramagnetic, and ferromagnetic Mn2+ ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N revealed that the localized Mn2+ ground state and Mn2+ state hybridized with ligand hole coexisted, implying p-d exchange coupling. In the valence-band spectra, spectral weight near the Fermi level was suppressed, suggesting that interaction between magnetic moments in ZnO:Mn,N has localized nature.
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71.20.Nr Semiconductor compounds
71.70.Gm Exchange interactions
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.70.Ak Magnetic properties of monolayers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Exploring Co2MnAl Heusler compound for anomalous Hall effect sensors

E. Vilanova Vidal, G. Stryganyuk, H. Schneider, C. Felser, and G. Jakob

Appl. Phys. Lett. 99, 132509 (2011); http://dx.doi.org/10.1063/1.3644157 (3 pages) | Cited 3 times

Online Publication Date: 27 September 2011

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Sets of Heusler compound Co2MnAl thin films were grown on MgO (100) and Si (100) substrates by radio frequency magnetron sputtering. Composition, magnetic, and transport properties were studied systematically for samples deposited at different conditions. In particular, the anomalous Hall effect resistivity presents an extraordinarily temperature independent behavior in a moderate magnetic field range from 0 to 0.6 T. We analyzed the off-diagonal transport at temperatures up to 300 °C. Our data show the suitability of the material for Hall sensors working well above room temperature.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
68.55.at Other materials
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.61.At Metal and metallic alloys
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering

Unveiling the (De)coupling of magnetostructural transition nature in magnetocaloric R5Si2Ge2 (R = Tb, Gd) materials

A. M. Pereira, E. Kampert, J. M. Moreira, U. Zeitler, J. H. Belo, C. Magen, P. A. Algarabel, L. Morellon, M. R. Ibarra, J. N. Gonçalves, J. S. Amaral, V. S. Amaral, J. B. Sousa, and J. P. Araújo

Appl. Phys. Lett. 99, 132510 (2011); http://dx.doi.org/10.1063/1.3640213 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2011

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We present a detailed study on the magnetization under high magnetic fields of Tb5Si2Ge2 and Gd5Si2Ge2 compounds. From the Arrott plot construction (A. Arrott, Phys. Rev. 108, 1394 (1957)), we were able to estimate the TC of each structure (M and O(I)) experimentally and found that the TC of the O(I) phase can be directly obtained by extrapolating the TC curve of this phase in the respective phase diagram. Using a physical model based on free energy considerations, one explains the (de)coupling of the magnetic and structural transitions in R5(SixGe1−x)4 (R = Tb, Gd) compounds.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
64.70.K- Solid-solid transitions
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals

Electric-field control of spin accumulation signals in silicon at room temperature

Y. Ando, Y. Maeda, K. Kasahara, S. Yamada, K. Masaki, Y. Hoshi, K. Sawano, K. Izunome, A. Sakai, M. Miyao, and K. Hamaya

Appl. Phys. Lett. 99, 132511 (2011); http://dx.doi.org/10.1063/1.3643141 (3 pages) | Cited 18 times

Online Publication Date: 28 September 2011

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We demonstrate spin accumulation signals controlled by the gate voltage in a metal-oxide-semiconductor field effect transistor structure with a Si channel and a CoFe/n+-Si contact at room temperature. Under the application of a back-gate voltage, we clearly observe the three-terminal Hanle-effect curves, i.e., spin accumulation signals. The magnitude of spin accumulation signals can be reduced with increasing the gate voltage. We consider that the gate controlled spin signals are attributed to the change in the carrier density in the Si channel beneath the CoFe/n+-Si contact. This study is not only a technological jump for Si-based spintronic applications with gate structures but also reliable evidence for the spin injection into the semiconducting Si channel at room temperature.
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85.75.Hh Spin polarized field effect transistors
85.30.Tv Field effect devices

Resistive switching at manganite/manganite interfaces

Christin Kalkert, Jon-Olaf Krisponeit, Markus Esseling, Oleg I. Lebedev, Vasily Moshnyaga, Bernd Damaschke, Gustaaf van Tendeloo, and Konrad Samwer

Appl. Phys. Lett. 99, 132512 (2011); http://dx.doi.org/10.1063/1.3643425 (3 pages) | Cited 3 times

Online Publication Date: 28 September 2011

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We report bipolar resistive switching between the interfaces of manganite nanocolumns. La0.7Sr0.3MnO3 films were prepared on Al2O3 substrates, where the films grow in nanocolumns from the substrate to the surface. Conductive atomic force microscopy directly detects that the resistive switching is located at the boundaries of the grains. Furthermore, mesoscopic transport measurements reveal a tunnel magnetoresistance. In combination with the resistive switching, this leads to a total of four different resistive states.
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75.47.Pq Other materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.78.Jp Ultrafast magnetization dynamics and switching
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
68.37.Ps Atomic force microscopy (AFM)

Spin transistor using magnetic tunnel junctions with half-metallic Co2MnSi Heusler alloy electrodes

Y. Ohdaira, M. Oogane, H. Naganuma, and Y. Ando

Appl. Phys. Lett. 99, 132513 (2011); http://dx.doi.org/10.1063/1.3645637 (3 pages) | Cited 2 times

Online Publication Date: 29 September 2011

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We fabricated a spin transistor structure that consisted of two magnetic tunnel junctions with half-metallic Co2MnSi electrodes. Transient responses were observed by applying pulsing gate voltage. Output currents were controlled by both the source-drain and gate voltage and magnetic configuration of the Co2MnSi. The drain current increased around 3000 times at a source-drain voltage of 0.01 V and anti-parallel magnetic configuration, when a gate voltage of 1 V peak-to-peak was applied. In addition, the maximum magnetocurrent ratios were 215% at 6 K. Expected operation properties are observed in our proposed spin transistor.
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75.47.Np Metals and alloys
75.76.+j Spin transport effects
72.25.Ba Spin polarized transport in metals
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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