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29 Aug 2011

Volume 99, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

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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Carrier capture into semiconductor quantum dots via quantum wire barriers: Localization and thermionic emission effects

J. Szeszko, Q. Zhu, P. Gallo, A. Rudra, and E. Kapon

Appl. Phys. Lett. 99, 091910 (2011); http://dx.doi.org/10.1063/1.3628320 (3 pages)

Online Publication Date: 2 September 2011

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Carrier transport and capture paths via barriers of different dimensionality in AlGaAs/GaAs quantum wire (QWR)/quantum dot (QD) heterostructures, grown in inverted pyramids, are studied by photoluminescence (PL) spectroscopy. Evidence for thermally activated diffusion related to potential disorder in the QWR barriers and thermionic emission of carriers from the QD into the QWR barrier is observed in temperature dependent PL spectra. Similar activation energies for the thermionic emission are derived from the continuous-wave and time-resolved PL spectroscopy.
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72.20.Fr Low-field transport and mobility; piezoresistance
78.55.Cr III-V semiconductors
79.40.+z Thermionic emission
68.65.Hb Quantum dots (patterned in quantum wells)
73.63.Kv Quantum dots
78.67.Hc Quantum dots
66.30.Pa Diffusion in nanoscale solids
68.65.La Quantum wires (patterned in quantum wells)
73.21.Hb Quantum wires
73.63.Nm Quantum wires
78.67.Lt Quantum wires
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Zinc-oxide-based planar nanodiodes operating at 50 MHz

Mustafa Y. Irshaid, Claudio Balocco, Yi Luo, Peng Bao, Christian Brox-Nilsen, and A. M. Song

Appl. Phys. Lett. 99, 092101 (2011); http://dx.doi.org/10.1063/1.3629995 (3 pages)

Online Publication Date: 29 August 2011

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Nanometer-scale self-switching devices (SSDs) fabricated in polycrystalline zinc oxide have been demonstrated up to at least 51.5 MHz, functioning as rectifiers to generate DC voltage. The SSDs require only a single nanolithography step and hence are of interest to low-cost printed electronics. The devices showed stable performance within the frequency range tested. The as-fabricated devices possessed strongly nonlinear current-voltage characteristics, resembling those of conventional diodes. After coating the devices with poly methyl methacrylate and poly vinylidene fluoride to enhance the electric field coupling, the nonlinear behavior was maintained while the device current increased dramatically.
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85.30.Kk Junction diodes
85.35.-p Nanoelectronic devices

Enhancing single-parameter quantum charge pumping in carbon-based devices

Luis E. F. Foa Torres, Hernán L. Calvo, Claudia G. Rocha, and Gianaurelio Cuniberti

Appl. Phys. Lett. 99, 092102 (2011); http://dx.doi.org/10.1063/1.3630025 (3 pages) | Cited 6 times

Online Publication Date: 29 August 2011

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We present a theoretical study of quantum charge pumping with a single ac gate applied to graphene nanoribbons and carbon nanotubes operating with low resistance contacts. By combining Floquet theory with Green’s function formalism, we show that the pumped current can be tuned and enhanced by up to two orders of magnitude by an appropriate choice of device length, gate voltage intensity, and driving frequency and amplitude. These results offer a promising alternative for enhancing the pumped currents in these carbon-based devices.
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85.35.Kt Nanotube devices

Strain modulated magnetization and colossal resistivity of epitaxial La2/3Ca1/3MnO3 film on BaTiO3 substrate

Z. X. Cheng, X. L. Wang, S. X. Dou, M. Osada, and H. Kimura

Appl. Phys. Lett. 99, 092103 (2011); http://dx.doi.org/10.1063/1.3633101 (3 pages) | Cited 3 times

Online Publication Date: 30 August 2011

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A sharp drop in resistance and a magnetization anomaly have been observed in La2/3Ca1/3MnO3 film in zero magnetic field at the BaTiO3 substrate structural phase transition temperature, due to the substrate clamping/strain effect, which is confirmed by Raman scattering. However, the anomalies for both resistance and magnetization were eliminated by a strong external magnetic field. These phenomena indicate that strain can cause colossal resistance and a change in magnetization which resembles the magnetic field effect. The interplay of the external forces (strain and magnetic field) is a good demonstration of the strong coupling between spin and lattice in colossal magnetoresistance materials.
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75.47.Gk Colossal magnetoresistance
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.80.+q Magnetomechanical effects, magnetostriction
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

On the high-field transport and its temperature dependence in deca-nanometer fully depleted silicon-on-insulator field-effect-transistor

Masaharu Kobayashi, Jin Cai, and Wilfried Haensch

Appl. Phys. Lett. 99, 092104 (2011); http://dx.doi.org/10.1063/1.3626849 (3 pages)

Online Publication Date: 30 August 2011

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Low-temperature characterization has been performed on fully depleted silicon-on-insulator (FDSOI) field-effect-transistor (FET) with gate length (Lg) down to 25 nm to clarify transport mechanisms that determine device performance in deca-nanometer scale. Linear drain current of FDSOI FET follows Lg−1 scaling down to 25 nm Lg, where mobility dominates, while saturation drain current largely deviates from Lg−1 scaling. Temperature dependence of effective source velocity at high drain voltage (Vds) is weaker than that at low Vds in short Lg and is consistent with that of saturation velocity. Drift velocity measurement revealed velocity overshooting behavior at high lateral field, indicating further Lg scaling benefit.
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85.30.Tv Field effect devices

Efficient resistive memory effect on SrTiO3 by ionic-bombardment

Heiko Gross and Seongshik Oh

Appl. Phys. Lett. 99, 092105 (2011); http://dx.doi.org/10.1063/1.3633114 (3 pages) | Cited 6 times

Online Publication Date: 31 August 2011

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We show that ionic-bombardment leads to noticeable resistive memory effect on pure SrTiO3 (STO). In an Ar-bombarded STO crystal, two orders of resistance difference was observed between the high and low resistive states. We found that Ar-bombardment is more efficient than thermal-reduction in creating memory-effective oxygen vacancies. One of the advantages of the ionic-bombardment scheme is that it can be easily combined with lithographic processes to create spatially selective memory effect.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.72.jd Vacancies
61.80.Jh Ion radiation effects
61.82.Ms Insulators
72.80.Sk Insulators

Investigation for coexistence of dual resistive switching characteristics in DyMn2O5 memory devices

Yu-Ting Tsai, Ting-Chang Chang, Wei-Li Huang, Chih-Wen Huang, Yong-En Syu, Shih-Cheng Chen, Simon M. Sze, Ming-Jinn Tsai, and Tseung-Yuen Tseng

Appl. Phys. Lett. 99, 092106 (2011); http://dx.doi.org/10.1063/1.3629788 (3 pages) | Cited 5 times

Online Publication Date: 1 September 2011

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Dual bipolar resistive switching characteristics were observed in the Pt/DyMn2O5/TiN memory devices. The typical switching effect could be attributed to the formation and rupture of the conducting filament in DyMn2O5 films. The parasitic switching behavior can be observed in the specific operation condition. Dual bipolar resistance switching behaviors of filament-type and interface-type can coexist in the devices by appropriate voltage operation. The operating current can be significantly decreased (100 times) by parasitic switching operation for portable electronic product application. In addition, the relationship between filament-type and interface-type switching behaviors were studied in this paper.
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84.30.Sk Pulse and digital circuits

Metal/III-V effective barrier height tuning using atomic layer deposition of high-κ/high-κ bilayer interfaces

Jenny Hu, Krishna C. Saraswat, and H.-S. Philip Wong

Appl. Phys. Lett. 99, 092107 (2011); http://dx.doi.org/10.1063/1.3633118 (3 pages) | Cited 11 times

Online Publication Date: 1 September 2011

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In this work, we use thin dielectrics to reduce the Al/n-GaAs effective barrier height (ΦB,eff) of metal-insulator-semiconductor (MIS) contacts. We investigate the use of atomic layer deposition of HfO2, Al2O3, TiO2, ZrO2, and bilayer high-κ dielectrics and confirm there is a shift in the Fermi level that reduces the contact resistance. In studying high-κ/high-κ interfaces, we find that despite a thicker dielectric, there is further reduction in ΦB,eff beyond that of a single dielectric, which can be explained by the formation of a high-κ/high-κ dipole. This MIS structure provides great flexibility in the design of source/drain contacts for III-V transistors.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Ns Metal-nonmetal contacts
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Cg Contact resistance, contact potential

Esaki tunnel diodes based on vertical Si-Ge nanowire heterojunctions

Wayne Y. Fung, Lin Chen, and Wei Lu

Appl. Phys. Lett. 99, 092108 (2011); http://dx.doi.org/10.1063/1.3633347 (3 pages) | Cited 1 time

Online Publication Date: 1 September 2011

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High performance Esaki tunnel diodes [L. Esaki, Phys. Rev. 109, 603 (1958)] based on small-diameter Ge/Si core/shell nanowires vertically grown on Si substrates are demonstrated. The devices exhibit pronounced negative differential resistance with peak-to-valley current ratio of 2.75, high peak current density of 2.4 kA/cm2, and high tunneling current density of 237 kA/cm2 at 1 V reverse bias, all obtained at room temperature. The peak current is found to increase with temperature and the data can be well explained with a band-to-band tunneling model. These results suggest that Si-Ge heterojunction with low defect density can be obtained for device applications such as tunnel diodes and tunnel field-effect transistors.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

Detailed characterization of deep level defects in InGaN Schottky diodes by optical and thermal deep level spectroscopies

Emre Gür, Zeng Zhang, Sriram Krishnamoorthy, S. Rajan, and S. A. Ringel

Appl. Phys. Lett. 99, 092109 (2011); http://dx.doi.org/10.1063/1.3631678 (3 pages) | Cited 3 times

Online Publication Date: 1 September 2011

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Schottky diode properties of semitransparent Ag(4 nm)/Au(4 nm) metal stack on In0.2Ga0.8N were investigated and defect characterization was performed using capacitance deep level transient (DLTS) and optical spectroscopy (DLOS). DLTS measurements made on the In0.2Ga0.8N Schottky diodes, which displayed a barrier height of 0.66 eV, revealed the presence of two deep levels located at Ec-0.39 eV and Ec-0.89 eV with nearly identical concentrations of ∼1.2 × 1015 cm−3. Three deeper defect levels were observed by DLOS at Ec-1.45 eV, Ec-1.76 eV, and Ec-2.50 eV with concentrations of 1.3 × 1015cm−3, 3.2 × 1015cm−3, and 6.1 × 1016 cm−3, respectively. The latter, with its high trap concentration and energy position lying 0.4 eV above the valance band, suggests a possible role in compensation of carrier concentration, whereas the mid-gap positions of the other two levels imply that they will be important recombination-generation centers
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85.30.Kk Junction diodes
71.55.Eq III-V semiconductors
78.40.Fy Semiconductors
85.30.Hi Surface barrier, boundary, and point contact devices

Hole mobility increase in ultra-narrow Si channels under strong (110) surface confinement

Neophytos Neophytou and Hans Kosina

Appl. Phys. Lett. 99, 092110 (2011); http://dx.doi.org/10.1063/1.3631680 (3 pages) | Cited 2 times

Online Publication Date: 2 September 2011

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We report on the hole mobility of ultra-narrow [110] Si channels as a function of the confinement length scale. We employed atomistic bandstructure calculations and linearized Boltzmann transport approach. The phonon-limited mobility of holes in thin [110] channels can be improved by more than 3 × as the thickness of the (110) confining surface is reduced down to 3 nm. This behavior originates from confinement induced bandstructure changes that decrease the hole effective mass and the scattering rates. Our results provide explanations for recent mobility measurements in nanobelts of similar dimensions.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.63.Bd Nanocrystalline materials
72.20.Ee Mobility edges; hopping transport
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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 15 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 6 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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Microstructure basis for strong piezoelectricity in Pb-free Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 ceramics

Jinghui Gao, Dezhen Xue, Yu Wang, Dong Wang, Lixue Zhang, Haijun Wu, Shengwu Guo, Huixin Bao, Chao Zhou, Wenfeng Liu, Sen Hou, Ge Xiao, and Xiaobing Ren

Appl. Phys. Lett. 99, 092901 (2011); http://dx.doi.org/10.1063/1.3629784 (3 pages) | Cited 22 times

Online Publication Date: 29 August 2011

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Show Abstract
In this letter, we use transmission electron microscopy to study the microstructure feature of recently reported Pb-free piezoceramic Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 across its piezoelectricity-optimal morphotropic phase boundary (MPB) by varying composition and temperature, respectively. The domain structure evolutions during such processes show that in MPB regime, the domains become miniaturized down to nanometer size with a domain hierarchy, which coincides with the d33-maximum region. Further convergent beam electron diffraction measurement shows that rhombohedral and tetragonal crystal symmetries coexist among the miniaturized domains. Strong piezoelectricity reported in such a system is due to easy polarization rotation between the coexisting nano-scale tetragonal and rhombohedral domains.
Show PACS
77.65.-j Piezoelectricity and electromechanical effects
77.84.Cg PZT ceramics and other titanates
61.72.-y Defects and impurities in crystals; microstructure
81.30.Dz Phase diagrams of other materials
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
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