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13 Oct 2008

Volume 93, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 151101 (2008); http://dx.doi.org/10.1063/1.2996271 (3 pages)

Xuefeng Zeng and Hongrui Jiang
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Giant electric-field-induced magnetization in a magnetoelectric composite at high frequency

Jian-Ping Zhou, Yang-Yang Guo, Zengzhe Xi, Peng Liu, Shuyu Lin, Gang Liu, and Huai-Wu Zhang

Appl. Phys. Lett. 93, 152501 (2008); http://dx.doi.org/10.1063/1.2998699 (3 pages) | Cited 16 times

Online Publication Date: 13 October 2008

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Electric-field-induced magnetization (EIM) characteristics are investigated in a small 0.68[Pb(Mg1/3Nb2/3)O3]0.32PbTiO3/Terfenol-D bilayered composite by using double coils in a wide frequency range of 10–700 kHz. The EIM behaviors are strongly dependent on driving electric field frequency, bias magnetic field, and angle θ between the bias magnetic field and polarization direction. The magnetoelectric coefficient at electromechanical resonance frequency of 185 kHz reaches up to 3.1×10−7 s/m, which is ∼ 60 times higher than the values at nonresonance frequency. The EIM variations with the bias magnetic field exhibit hysteresis, forming EIM hysteresis loops caused by the magnetostrictive hysteresis from Terfenol-D.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Switching magnetic vortex core by a single nanosecond current pulse

Keisuke Yamada, Shinya Kasai, Yoshinobu Nakatani, Kensuke Kobayashi, and Teruo Ono

Appl. Phys. Lett. 93, 152502 (2008); http://dx.doi.org/10.1063/1.3001588 (3 pages) | Cited 24 times

Online Publication Date: 14 October 2008

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In a ferromagnetic nanodisk, the magnetization tends to swirl around in the plane of the disk and can point either up or down at the center of this “magnetic vortex.” This binary state can be useful for information storage. It is demonstrated that a single nanosecond current pulse can switch the core polarity. This method also provides the precise control of the core direction, which constitutes fundamental technology for realizing a vortex core memory.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic-field-induced strain assisted by tensile stress in L10 martensite of a Ni–Fe–Ga–Co alloy

F. Masdeu, J. Pons, E. Cesari, S. Kustov, and Y. I. Chumlyakov

Appl. Phys. Lett. 93, 152503 (2008); http://dx.doi.org/10.1063/1.2998696 (3 pages) | Cited 4 times

Online Publication Date: 14 October 2008

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Magnetic-field-induced strains larger than 2% have been obtained in the nonlayered L10 martensite of a Ni49Fe18Ga27Co6 single crystal, under an assisting tensile stress around 16 MPa and fields below 15 kOe. In martensitic samples previously compressed, application of a constant tensile stress along the same axis together with a perpendicular magnetic field produces the elongation of the sample, as one of the variants rotates its c axis from the field direction to the stress-axis direction. An estimated magnetostress of ∼ 0.8 MPa is in good agreement with the theoretical value given by the ratio of magnetocrystalline anisotropy constant and twinning shear.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
75.30.Gw Magnetic anisotropy

Propagation of exchange bias in CoFe/FeMn/CoFe trilayers

D. N. H. Nam, W. Chen, K. G. West, D. M. Kirkwood, J. Lu, and S. A. Wolf

Appl. Phys. Lett. 93, 152504 (2008); http://dx.doi.org/10.1063/1.2999626 (3 pages) | Cited 4 times

Online Publication Date: 14 October 2008

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CoFe/FeMn, FeMn/CoFe bilayers and CoFe/FeMn/CoFe trilayers were grown in magnetic field and at room temperature. The exchange bias field HEB depends strongly on the order of depositions and is much higher at CoFe/FeMn than at FeMn/CoFe interfaces. By combining the two bilayer structures into symmetric CoFe/FeMn(tFeMn)/CoFe trilayers, HEBt and HEBb of the top and bottom CoFe layers, respectively, are both enhanced. Reducing tFeMn of the trilayers also results in enhancements of both HEBb and HEBt. These results evidence the propagation of exchange bias between the two CoFe/FeMn and FeMn/CoFe interfaces mediated by the FeMn antiferromagnetic order.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys

Superconductivity at 27 K in tetragonal FeSe under high pressure

Yoshikazu Mizuguchi, Fumiaki Tomioka, Shunsuke Tsuda, Takahide Yamaguchi, and Yoshihiko Takano

Appl. Phys. Lett. 93, 152505 (2008); http://dx.doi.org/10.1063/1.3000616 (3 pages) | Cited 231 times

Online Publication Date: 15 October 2008

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A huge enhancement of the superconducting transition temperature Tc was observed in a tetragonal FeSe superconductor under high pressure. The onset temperature was as high as 27 K at 1.48 GPa and the pressure coefficient showed an extremely high value of 9.1 K/GPa. The upper critical field Hc2 was estimated to be ∼ 72 T at 1.48 GPa. Because of the high Hc2, the FeSe system can be applied to superconducting wire rods.
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74.62.Fj Effects of pressure
62.50.-p High-pressure effects in solids and liquids
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.10.+v Occurrence, potential candidates
74.25.Op Mixed states, critical fields, and surface sheaths

Vortex Bose glass in ErBa2Cu3Oy films with size-controlled nanorods

S. Horii, H. Kai, M. Mukaida, K. Yamada, R. Teranishi, A. Ichinose, K. Matsumoto, Y. Yoshida, R. Kita, J. Shimoyama, and K. Kishio

Appl. Phys. Lett. 93, 152506 (2008); http://dx.doi.org/10.1063/1.3001603 (3 pages) | Cited 15 times

Online Publication Date: 15 October 2008

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Anomalous changes in irreversibility lines (ILs) and critical current properties depending on growth conditions were demonstrated in ErBa2Cu3Oy films with Ba–(Nb,Er)–O nanorods. Despite the formation of nanorods in the matrix at all growth temperatures (Ts), Bose-glass-like vortex pinning was strengthened with decreasing Ts. In particular, the behavior of ILs can be understood in terms of the morphology of introduced nanorods, and Ts strongly affects the vortex states. Our present study suggests the importance of optimization of growth conditions in the production process of rare-earth-based coated conductors containing nanorods as vortex-pinning centers.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents

Effects of the thickness asymmetry of nanostructured exchange-coupled trilayers on their dynamic magnetization switching

K. S. Kim, K. J. Lee, and S. H. Lim

Appl. Phys. Lett. 93, 152507 (2008); http://dx.doi.org/10.1063/1.3001805 (3 pages) | Cited 5 times

Online Publication Date: 15 October 2008

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The effects of thickness asymmetry (Δt) on the dynamic magnetization switching of exchange-coupled trilayers are investigated in this study. Elliptical thin films that have lateral dimensions of 200×100 nm2 are considered. A significant difference in the dynamic switching behavior is observed depending on Δt. Both the switching field and the switching time decrease as Δt increases. A Fourier analysis of the magnetization oscillation, which is followed by the initial coherent rotation, shows multiple oscillation frequencies. This tendency is more pronounced at a larger Δt. The main oscillation frequency tends to increase with an increase in Δt.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
02.30.Nw Fourier analysis
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Et Exchange and superexchange interactions

Direct imaging of the structural change generated by dielectric breakdown in MgO based magnetic tunnel junctions

A. Thomas, V. Drewello, M. Schäfers, A. Weddemann, G. Reiss, G. Eilers, M. Münzenberg, K. Thiel, and M. Seibt

Appl. Phys. Lett. 93, 152508 (2008); http://dx.doi.org/10.1063/1.3001934 (3 pages) | Cited 7 times

Online Publication Date: 15 October 2008

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MgO based magnetic tunnel junctions are prepared to investigate the dielectric breakdown of the barrier. The breakdown is visualized by transmission electron microscopy measurements. The broken tunnel junctions are prepared for the microscopy measurements by focused ion beam out of the junctions characterized by transport investigations. A direct comparison of transport behavior and structure of the intact and broken junctions is obtained. The MgO barrier shows many microscopic pinholes after breakdown. This can be explained within a model assuming a relationship between the current density at the breakdown and the rate of pinhole formation.
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72.25.-b Spin polarized transport
77.22.Jp Dielectric breakdown and space-charge effects
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Pulsed laser deposition of ferromagnetic Zn0.95Co0.05O thin films

Milan Gacic, Hermann Adrian, and Gerhard Jakob

Appl. Phys. Lett. 93, 152509 (2008); http://dx.doi.org/10.1063/1.3005413 (3 pages) | Cited 7 times

Online Publication Date: 16 October 2008

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Zn0.95Co0.05O thin films have been prepared by pulsed laser deposition at different preparation conditions. By optimizing the deposition parameters we were able to increase the reproducibility of our ferromagnetic films up to 50% as well as the magnetization to 2.3μB/Co. The ferromagnetic properties could be improved by a special multilayered deposition technique. Investigations of the magnetic and magnetotransport properties showed a clear correlation between the magnetic properties and the deposition conditions as well as a clear dependence between the transport and the magnetic properties. This hints to an intrinsic origin of the ferromagnetism.
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81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films

Experimental manifestation of the breakpoint region in the current-voltage characteristics of intrinsic Josephson junctions

A. Irie, Yu. M. Shukrinov, and G. Oya

Appl. Phys. Lett. 93, 152510 (2008); http://dx.doi.org/10.1063/1.3005418 (3 pages) | Cited 9 times

Online Publication Date: 16 October 2008

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The experimental evidence of the breakpoint on the current-voltage characteristics (IVCs) of the stacks of intrinsic Josephson junctions (IJJs) is presented. The influence of the capacitive coupling on the IVCs of Bi2Sr2CaCu2Oy IJJs has been investigated. At 4.2 K, clear breakpoint region is observed on the branches in the IVCs. It is found that due to the coupling between junctions, the hysteresis observed on the IVC is small compared to that expected from the McCumber parameter. Measurements agree well with the results predicted by the capacitively coupled Josephson junction model including the diffusion current.
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74.50.+r Tunneling phenomena; Josephson effects
74.81.Fa Josephson junction arrays and wire networks
74.25.F- Transport properties
74.72.-h Cuprate superconductors

Controlled fabrication of SnO2 solid and hollow nanocubes with a simple hydrothermal route

Liang Shi, Keyan Bao, Jie Cao, and Yitai Qian

Appl. Phys. Lett. 93, 152511 (2008); http://dx.doi.org/10.1063/1.2952758 (3 pages) | Cited 5 times

Online Publication Date: 16 October 2008

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SnO2 solid and hollow nanocubes have been fabricated by a one-step hydrothermal treatment of tin foil in aqueous alkaline solutions at 200 °C. The obtained cubes have an average edge length of about 300 nm, and the thickness of the hollow cubes’ shell is in the range of 30–50 nm. Based on the time-dependent experiments, the evacuation behavior of Ostwald ripening is proposed to explain the formation mechanism of hollow cubes. Cathodoluminescence measurements disclose that the intensity for two peaks of hollow SnO2 nanocubes is enhanced significantly with respect to that of solid nanocubes.
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81.16.-c Methods of micro- and nanofabrication and processing
81.10.Dn Growth from solutions
78.60.Hk Cathodoluminescence, ionoluminescence

Thermal stability of ledge-type L10-FePt/Fe exchange-spring nanocomposites for ultrahigh recording densities

D. Goll and S. Macke

Appl. Phys. Lett. 93, 152512 (2008); http://dx.doi.org/10.1063/1.3001589 (3 pages) | Cited 15 times

Online Publication Date: 17 October 2008

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Long-term thermal stability is crucial for magnetic nanoparticles in ultrahigh density magnetic recording. For ledge-type exchange-spring nanocomposites consisting of a hard magnetic L10-FePt part and a soft magnetic Fe part of more extended horizontal size, the minimum energy barriers for thermal reversal between equilibrium states of the hysteresis loops are determined using a nudged-elastic-band path approach. The field dependence of the energy barrier can be described approximately by power laws. It turns out that nanopatterns of isolated ledge-type L10-FePt/Fe composite elements or isolated L10-FePt nanodots covered by a thin Fe film are well-suited in realizing ultrahigh recording densities.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Ss Magnetic recording materials
75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic properties and microstructure of FePt/Au multilayers with high perpendicular magnetocrystalline anisotropy

Chun Feng, Qian Zhan, Baohe Li, Jiao Teng, Minghua Li, Yong Jiang, and Guanghua Yu

Appl. Phys. Lett. 93, 152513 (2008); http://dx.doi.org/10.1063/1.3001801 (3 pages) | Cited 12 times

Online Publication Date: 17 October 2008

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FePt/Au multilayers were deposited on preheated 100 °C MgO (001) single crystal substrates by magnetron sputtering. Magnetic properties and microstructure of the films were studied. Results show that the film possesses high coercivity HC, excellent perpendicular magnetic anisotropy (PMA), and weak interparticle exchange coupling (IEC) after annealing. FePt and Au can grow epitaxially on MgO substrates along the [001] direction, leading to excellent PMA. Au atoms partly diffuse to the boundaries of FePt phases and function as grain refiners and particle isolators, which markedly decrease the FePt grain size and IEC. Moreover, the additional FePt/Au interface energy, the stress energy due to the mismatch between FePt and Au lattices, and the diffusion of Au atoms all promote the ordering process of FePt film. This leads to the decrease in ordering temperature by 150 °C and a considerable increase in HC.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.50.Ss Magnetic recording materials
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments

Magnetic cluster size and cluster size distribution study on perpendicular media

X. W. Wu, Yingguo Peng, and Binquan Wang

Appl. Phys. Lett. 93, 152514 (2008); http://dx.doi.org/10.1063/1.3001804 (3 pages) | Cited 4 times

Online Publication Date: 17 October 2008

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For granular media, the cluster size is closely related to the grain size and, at the same time, strongly affected by the intergranular exchange coupling strength. We develop the minimum-width detection scheme to analyze the magnetic cluster size and cluster size distribution for perpendicular media. We observed that the median magnetic cluster size strongly depends on the intergranular exchange interaction strength. For the exchange decoupled sample, the magnetic cluster size is close to the grain size of 7.6 nm. With increasing magnitude of the exchange interaction, the cluster size increases to about 19 nm for Hex = 10 kOe. Similar to the median cluster size, the standard deviation of the magnetic cluster size also increases with increasing exchange interaction strength. However, the fractional standard deviation of the cluster size, defined as the ratio between the distribution and the median cluster size, shows little dependency on the intergranular exchange interaction strength.
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75.50.Ss Magnetic recording materials
75.30.Et Exchange and superexchange interactions

Charge ordering transition near the interface of the (011)-oriented La1−xSrxMnO3 (x ∼ 1/8) films

Y. Z. Chen, J. R. Sun, A. D. Wei, W. M. Lu, S. Liang, and B. G. Shen

Appl. Phys. Lett. 93, 152515 (2008); http://dx.doi.org/10.1063/1.3003868 (3 pages) | Cited 11 times

Online Publication Date: 17 October 2008

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Two clear phase transitions, an insulator to metal transition followed by a metal to insulator transition on cooling, were realized in La1−xSrxMnO3 (x ∼ 1/8) (LSMO) thin films grown on (011) SrTiO3 substrates due to the substrate-imposed anisotropic stain. Effects of phase transitions on the rectifying behavior of the corresponding junction LSMO/Nb:SrTiO3 were further investigated. The paramagnetic/insulator to ferromagnetic/metal transition led to a decrease in built-in potential of the junction, while the metallic to charge/orbital ordering transition results in a growth of interfacial barrier, which could be explained by Fermi-level shifts and the gap opening/closing in LSMO films. These results indicate the occurrence of clear phase transitions in the vicinity of interface in (011)-LSMO films.
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71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Lx Magnetic oxides
73.40.Ei Rectification

Extending the Snoek’s limit of single layer film in (Co96Zr4/Cu)n multilayers

Guozhi Chai, Desheng Xue, Xiaolong Fan, Xiling Li, and Dangwei Guo

Appl. Phys. Lett. 93, 152516 (2008); http://dx.doi.org/10.1063/1.3003876 (3 pages) | Cited 10 times

Online Publication Date: 17 October 2008

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The present work investigates the high frequency characteristics of (Co96Zr4/Cu)n multilayers. The results reveal that the Snoek’s limit of (Co96Zr4/Cu)n multilayers (revised Acher’s limit) are much larger (as a fact 1.76 for some samples) than that of single layer {Acher’s limit [ O. Acher and A. L. Adenot, Phys. Rev. B 62, 11324 (2000)] } by comparing their static and dynamic magnetism. It is found that the differences of Acher’s limit between multilayers and single layers are caused by magnetic interface anisotropy. This work might facilitate search for new materials with high permeability at high frequency.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
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