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29 Aug 2011

Volume 99, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 99, 094101 (2011); http://dx.doi.org/10.1063/1.3629783 (3 pages)

Tomasz Szymborski, Piotr M. Korczyk, Robert Hołyst, and Piotr Garstecki
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Fourier magnetic imaging

T. Verduci, C. Rufo, A. Berger, V. Metlushko, B. Ilic, and P. Vavassori

Appl. Phys. Lett. 99, 092501 (2011); http://dx.doi.org/10.1063/1.3630049 (3 pages) | Cited 5 times

Online Publication Date: 29 August 2011

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We present a methodology for the extraction of the spatial Fourier components of the magnetization profile for an array of nanosized magnetic objects, from diffracted magneto optic Kerr effect measurements. The field dependent magnetization configuration in the unit cell is retrieved by inverse Fourier transform and compared with the predictions of micromagnetic simulations. The comparison demonstrates that the methodology is a powerful optical tool for lens-less diffraction-limited optical imaging of the collective magnetic behavior of nano-structures.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Continuously tunable magnetic phase transitions in the DyMn1−xFexO3 system

Fang Hong, Zhenxiang Cheng, Hongyang Zhao, Hideo Kimura, and Xiaolin Wang

Appl. Phys. Lett. 99, 092502 (2011); http://dx.doi.org/10.1063/1.3632061 (3 pages) | Cited 4 times

Online Publication Date: 29 August 2011

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The structure and magnetic properties of perovskite DyMn1−xFexO3 samples have been studied. Static orbital orderings are expected to exist in samples with x ≤ 0.2 due to strong Jahn-Teller distortion, which become less stable as x increases and probably disappears in samples with x > 0.5. The antiferromagnetic transition temperature increases as x increases. At the composition x > 0.5, spin reorientation starts to appear. Meanwhile, the spin reorientation temperature and the antiferromagnetic Néel temperature gradually separate and widen the temperature range of the magnetic metastable state between these two transitions. The magnetic competition is discussed based on exchange interaction and Dzyaloshinsky-Moriya interaction.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Ee Antiferromagnetics
75.85.+t Magnetoelectric effects, multiferroics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Et Exchange and superexchange interactions

Negative remanent magnetization in a single domain particle with two uniaxial anisotropies

Yoon Jae Nam and S. H. Lim

Appl. Phys. Lett. 99, 092503 (2011); http://dx.doi.org/10.1063/1.3633107 (3 pages)

Online Publication Date: 30 August 2011

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The unusual behavior of negative remanent magnetization (NRM) that is observed in a simple homogeneous system consisting of two uniaxial anisotropies is explained quantitatively using an energy equation derived under the single domain assumption. The relative strength and alignment of the two uniaxial anisotropies and the direction of the applied magnetic field with respect to these anisotropies are identified as the three important factors for NRM. The window showing NRM is wider at larger angles between the two anisotropies and a maximum in NRM occurs near the boundary between NRM and ordinary positive remanent magnetization.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Temperature dependences of the spin transfer torque and tunneling magneto-resistance in magnetic metallic and tunneling junctions

Chun-Yeol You, Seung-Ho Song, and Hyungsuk Kim

Appl. Phys. Lett. 99, 092504 (2011); http://dx.doi.org/10.1063/1.3631663 (3 pages) | Cited 1 time

Online Publication Date: 30 August 2011

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We investigate temperature dependences of the spin transfer torque (STT) and tunneling magnetoresistance (TMR) in the magnetic metallic junction (MMJ) and magnetic tunneling junction (MTJ). The temperature dependences of the in-plane and out-of-plane STTs are calculated with the Keldysh non-equilibrium Green’s function method. We find that the temperature dependences of the in-plane and out-of-plane STTs for MTJ are strikingly deviated from the previous prediction [P. Bruno, Phys. Rev. B 52, 411 (1995)] for the interlayer exchange coupling, while ones for MMJ are well agreed with the prediction. Furthermore, the temperature dependences of the in-plane and out-of-plane STTs are varied with the bias voltage in different ways.
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72.25.-b Spin polarized transport
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.76.+j Spin transport effects

Magnetic switching fluctuations from sidewall oxides in MgO/FeCoB magnetic tunnel junctions

J. M. Pomeroy and J. C. Read

Appl. Phys. Lett. 99, 092505 (2011); http://dx.doi.org/10.1063/1.3631754 (3 pages) | Cited 1 time

Online Publication Date: 30 August 2011

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Sharp magnetic switching distributions with coupling to magnetic sidewall oxides in FeCoB/MgO magnetic tunnel junctions (MTJs) are revealed by magneto-resistance first order reversal curve (MR-FORC) measurements. Tunneling magneto-resistance (TMR) and FORC data in units of % TMR/mT2 are shown for two identical devices that differ only by the annealing. The annealed sample has much larger TMR and correspondingly higher switching density ρ. In both cases, the MR-FORC data exhibit a prominent “checkerboard” pattern that implies coupling to magnetic oxides on the MTJ sidewalls.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
75.50.Bb Fe and its alloys

Spin transfer torque switching for multi-bit per cell magnetic memory with perpendicular anisotropy

R. Sbiaa, R. Law, S. Y. H. Lua, E. L. Tan, T. Tahmasebi, C. C. Wang, and S. N. Piramanayagam

Appl. Phys. Lett. 99, 092506 (2011); http://dx.doi.org/10.1063/1.3632075 (3 pages) | Cited 5 times

Online Publication Date: 30 August 2011

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A novel multi-bit dual pseudo spin valve with perpendicular magnetic anisotropy is investigated for spin transfer torque (STT) switching. The structure consists of two free layers and one reference layer, and all are based on Co/Pd multilayer. STT switching of the multi-bit device shows distinct four resistance levels. The selection of intrinsic properties of each ferromagnetic layer can be controlled for distinct separation of the resistance levels as well as the respective STT switching current. Reversible transitions between different states can be achieved by a pulsed current, in which its critical value is found to be linearly dependent on pulse duration.
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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
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys

Enhancement of microwave oscillation under angled in-plane magnetic field in ferromagnetic nano-contact spin-valves

Hiroaki Suzuki, Tetsuya Nakamura, Hiroaki Endo, Masaaki Doi, Hiroshi Tsukahara, Hiroshi Imamura, Hiromi N. Fuke, Susumu Hashimoto, Hitoshi Iwasaki, and Masashi Sahashi

Appl. Phys. Lett. 99, 092507 (2011); http://dx.doi.org/10.1063/1.3619835 (3 pages) | Cited 2 times

Online Publication Date: 31 August 2011

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We investigated the microwave oscillation of resistance due to spin-transfer torque in ferromagnetic nano-contact spin-valves under an external in-plane magnetic field. We varied the direction of the external magnetic field and therefore the relative angle, θ, between magnetizations of the free and reference layers. We showed that the level of microwave oscillation takes a maximum value at around θ = 140°. We also showed that the microwave oscillation frequency increases with increases in the applied direct current.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Probing the magnetization inside a superconducting Nb film by nuclear resonant scattering

S. Couet, M. Trekels, R. Rüffer, J. Cuppens, C. Petermann, A. Vantomme, M. J. Van Bael, and K. Temst

Appl. Phys. Lett. 99, 092508 (2011); http://dx.doi.org/10.1063/1.3625941 (3 pages)

Online Publication Date: 31 August 2011

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We present an approach to probe the magnetization inside superconducting films using ultrathin 57Fe probe layers excited by synchrotron radiation. We investigate the evolution of the 57Fe hyperfine field orientation as a function of magnetic field above and below the superconducting transition temperature Tc for a Nb(50 nm)/57Fe(0.6 nm)/Nb(50 nm) trilayer. It is found that significant screening of the external field in the superconductor occurs only at low field, leading to a change in the hyperfine field angle below Tc. The presented approach allows to study the influence of magnetic fields and vortex induced electron correlations in complex layered structures incorporating superconductors.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.Fk Multilayers, superlattices, heterostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.70.Jp Nuclear states and interactions
74.10.+v Occurrence, potential candidates

Precessional dynamics and damping in Co/Cu/Py spin valves

R. Salikhov, R. Abrudan, F. Brüssing, St. Buschhorn, M. Ewerlin, D. Mishra, F. Radu, I. A. Garifullin, and H. Zabel

Appl. Phys. Lett. 99, 092509 (2011); http://dx.doi.org/10.1063/1.3633115 (3 pages) | Cited 3 times

Online Publication Date: 1 September 2011

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We have studied the precessional dynamics of Co/Cu/Py (where Py = Ni81Fe19) trilayers by time-resolved x-ray resonant magnetic scattering at the synchrotron radiation facility BESSY II. We have found that the magnetic precessional decay time of Fe magnetic moments in Py layers decreases when changing the mutual orientation of the magnetization direction of Py and Co layers from parallel to antiparallel. The observed changes of the decay time can be associated with the spin pumping induced damping effect.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.70.Ck X-ray scattering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Nonlinear spin pumping induced by parametric excitation

K. Ando, T. An, and E. Saitoh

Appl. Phys. Lett. 99, 092510 (2011); http://dx.doi.org/10.1063/1.3633348 (3 pages) | Cited 6 times

Online Publication Date: 1 September 2011

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Spin pumping driven by parametric spin excitation was observed in a Pt/La:Y3Fe5O12 film. We applied microwave with doubled frequency of the ferromagnetic resonance and detected a spin current emitted from the La:Y3Fe5O12 layer using the inverse spin-Hall effect (ISHE) in the Pt layer. In the ISHE signal, we found nonlinear dependence and threshold with respect to applied microwave power, demonstrating that the spin current generation is due to nonlinear coupling between microwave and spin dynamics. These results will be essential for developing active elements in spin current circuits.
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75.70.Ak Magnetic properties of monolayers and thin films
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
73.50.Mx High-frequency effects; plasma effects
75.76.+j Spin transport effects
72.25.Pn Current-driven spin pumping
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

From first-order magneto-elastic to magneto-structural transition in (Mn,Fe)1.95P0.50Si0.50 compounds

N. H. Dung, L. Zhang, Z. Q. Ou, and E. Brück

Appl. Phys. Lett. 99, 092511 (2011); http://dx.doi.org/10.1063/1.3634016 (3 pages) | Cited 14 times

Online Publication Date: 1 September 2011

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We report on structural, magnetic, and magnetocaloric properties of MnxFe1.95−xP0.50Si0.50 (x ≥ 1.10) compounds. With increasing the Mn:Fe ratio, a first-order magneto-elastic transition gradually changes into a first-order magneto-structural transition via a second-order magnetic transition. The study also shows that thermal hysteresis can be tuned by varying the Mn:Fe ratio. Small thermal hysteresis (less than 1 K) can be obtained while maintaining a giant magnetocaloric effect. This achievement paves the way for real refrigeration applications using magnetic refrigerants.
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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.)
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys

Twin boundary energy of hierarchically twinned magnetic shape memory alloys

Anett Diestel, Anja Backen, Ulrich K. Rößler, Ludwig Schultz, and Sebastian Fähler

Appl. Phys. Lett. 99, 092512 (2011); http://dx.doi.org/10.1063/1.3635382 (3 pages) | Cited 5 times

Online Publication Date: 2 September 2011

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Magnetic shape memory alloys exhibit a hierarchy of “twins within twins” microstructures, covering all length scale from nanometer to millimeter. Modulated structures as nano-twinned adaptive martensite are the first generation of twinning. Using epitaxial Ni-Mn-Ga films as model system, we observe a regular twinning of 14M modulated variants, which represent the second generation of twinning hierarchy. We analyzed a thickness series from 30 nm to 2 μm and found a square-root dependency of the twinning period on film thickness. From the Landau-Lifshitz-Kittel scaling law, the twin boundary energy between mesoscopic 14M modulated variants is estimated the value of 0.7 eV/Å2.
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61.72.Mm Grain and twin boundaries
68.55.jd Thickness

Reentrant insulating state in ultrathin manganite films

Bongju Kim, Daeyoung Kwon, Takeaki Yajima, Christopher Bell, Yasuyuki Hikita, Bog G. Kim, and Harold Y. Hwang

Appl. Phys. Lett. 99, 092513 (2011); http://dx.doi.org/10.1063/1.3628659 (3 pages) | Cited 4 times

Online Publication Date: 2 September 2011

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The transport and magnetic properties of La0.7Sr0.3MnO3 thin-films grown by pulsed laser deposition on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 single crystal substrates have been investigated. A systematic series with various thicknesses of La0.7Sr0.3MnO3 was used to establish a phase diagram which showed a clear difference compared to films grown on SrTiO3 substrates, highlighting the importance of film thickness, and substrate strain. At 8 unit cells, the boundary between the metallic and insulating groundstates, a second abrupt metal-insulator transition was observed at low temperatures, which could be tuned by magnetic field, and was interpreted as a signature of electronic phase separation.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ng Insulators
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.30.Dz Phase diagrams of other materials
81.15.Fg Pulsed laser ablation deposition
68.55.aj Insulators
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