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31 Jan 2011

Volume 98, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 053101 (2011); http://dx.doi.org/10.1063/1.3549154 (3 pages)

Minggang Zeng, Lei Shen, Ming Yang, Chun Zhang, and Yuanping Feng
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Fast magnetization precession observed in L10-FePt epitaxial thin film

S. Mizukami, S. Iihama, N. Inami, T. Hiratsuka, G. Kim, H. Naganuma, M. Oogane, and Y. Ando

Appl. Phys. Lett. 98, 052501 (2011); http://dx.doi.org/10.1063/1.3549704 (3 pages) | Cited 7 times

Online Publication Date: 31 January 2011

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Fast magnetization precession is observed in L10-FePt alloy epitaxial thin films excited and detected by all-optical means. The precession frequency varies from 45 to 65 GHz depending on the applied magnetic field strength and direction, which can be explained by a uniform precession model taking account of first- and second-order uniaxial magnetic anisotropy. The lowest effective Gilbert damping constant has a minimum value of 0.055, which is about half that in Co/Pt multilayers and is comparable to Ni/Co multilayers with perpendicular magnetic anisotropy.
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73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

Detecting single nanomagnet dynamics beyond the diffraction limit in varying magnetostatic environments

Z. Liu, R. Brandt, Y. Yahagi, B. Hansen, B. Harteneck, J. Bokor, A. R. Hawkins, and H. Schmidt

Appl. Phys. Lett. 98, 052502 (2011); http://dx.doi.org/10.1063/1.3549302 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2011

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As areal bit density increases, characterizing individual magnetic bits within dense arrays becomes difficult with diffraction-limited optics. We demonstrate that dynamic magneto-optical detection breaks this diffraction limit if the characteristic behavior of a nanomagnet is sufficiently different from its neighbors’. We use far-field time-resolved Kerr microscopy to resolve the high-frequency magnetization dynamics of a single, small (Ø150 nm) nanomagnet within a low-frequency background from an array of large (Ø500 nm) magnets. We use this technique to observe and quantify the effects of magnetostatic interactions on the single magnet dynamics as the intermagnet spacing is varied.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.20.Ls Magneto-optical effects
75.78.Jp Ultrafast magnetization dynamics and switching
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Correlation between saturation magnetization and surface morphological features in Zn1−xCrxO thin films

Y. M. Hu, S. S. Li, and C. H. Chia

Appl. Phys. Lett. 98, 052503 (2011); http://dx.doi.org/10.1063/1.3549696 (3 pages) | Cited 5 times

Online Publication Date: 1 February 2011

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The effect of chromium doping on the defect-induced ferromagnetism of Zn1−xCrxO films was investigated in this study. X-ray diffraction and x-ray photoelectron results confirm Cr substitution at Zn sites in the ZnO host lattice. A parabolic dependence of the saturation magnetization on the stoichiometric variable x was observed. Photoluminescence and magnetic results indicate that magnetic moments in Zn1−xCrxO films stem from Zn vacancies on the film surface or at grain boundaries. As the variation in saturation magnetization is consistent with that in surface morphology, the ferromagnetism in Zn1−xCrxO films is sensitive to the morphological modification caused by Cr doping.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.bg Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Hf II-VI semiconductors

Hysteresis and intermittency in direct-current superconducting quantum interference device with nanobridges fabricated on a thin membrane

Eran Segev, Oren Suchoi, Oleg Shtempluck, Fei Xue, and Eyal Buks

Appl. Phys. Lett. 98, 052504 (2011); http://dx.doi.org/10.1063/1.3549767 (3 pages)

Online Publication Date: 1 February 2011

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This study examined the voltage response of nanobridge-based direct-current superconducting quantum interference devices (dc-SQUIDs) fabricated on a Si3N4 membrane. Such a configuration may help in reducing 1/f noise, which possibly originates from substrate fluctuating defects. Results showed that the poor thermal coupling between the dc-SQUID and the substrate leads to a strong hysteretic response of the superconducting quantum interference device (SQUID) even though it is biased by an alternating current. In addition, when the dc-SQUID is biased near a threshold of spontaneous oscillations, the measured voltage has an intermittent pattern, which depends on the applied magnetic flux threading the loop of the SQUID.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.40.De Noise and chaos
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Large converse magnetoelectric effect in Metglas FeCoBSi and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite

H. C. Xuan, L. Y. Wang, S. C. Ma, Y. X. Zheng, Q. Q. Cao, D. H. Wang, and Y. W. Du

Appl. Phys. Lett. 98, 052505 (2011); http://dx.doi.org/10.1063/1.3549871 (3 pages) | Cited 9 times

Online Publication Date: 1 February 2011

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Converse magnetoelectric (CME) effect is investigated in a FeCoBSi/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite by using induction method within different frequencies. A large CME coefficient of 3.05 G/V is observed at the resonance frequency of 76.5 kHz under a low bias magnetic field of 50 Oe. The CME coefficient of the heterostructure is almost constant and exhibits a relatively high value in a wide frequency span of 1–64 kHz. The origin of large CME effect and the advantages of Metglas acting as ferromagnetic layer are discussed in the present paper.
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75.85.+t Magnetoelectric effects, multiferroics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Ferromagnetic carbon materials prepared from polyacrylonitrile

Tetsuji Saito, Daisuke Nishio-Hamane, Shunsuke Yoshii, and Tsutomu Nojima

Appl. Phys. Lett. 98, 052506 (2011); http://dx.doi.org/10.1063/1.3551522 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2011

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We report a ferromagnetic carbon material that is attracted by a permanent magnet. The ferromagnetic carbon material was prepared by pyrolysis of polyacrylonitrile at 1273 K for 1 h. Chemical analysis combined with an energy-dispersive x-ray analysis revealed that the carbon material did not contain any transition metals. The metal-free ferromagnetic carbon material exhibited a saturation magnetization of 1.22 emu/g at room temperature.
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81.20.-n Methods of materials synthesis and materials processing
61.41.+e Polymers, elastomers, and plastics
75.50.Ww Permanent magnets
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Memory-bit selection and recording by rotating fields in vortex-core cross-point architecture

Young-Sang Yu, Hyunsung Jung, Ki-Suk Lee, Peter Fischer, and Sang-Koog Kim

Appl. Phys. Lett. 98, 052507 (2011); http://dx.doi.org/10.1063/1.3551524 (3 pages) | Cited 5 times

Online Publication Date: 1 February 2011

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In one of our earlier studies S.-K. Kim et al., [Appl. Phys. Lett. 92, 022509 (2008)] , we proposed a concept of robust information storage, recording, and readout, which can be implemented in nonvolatile magnetic random-access memories and is based on the energetically degenerated twofold ground states of vortex-core magnetizations. In the present study, we experimentally demonstrate reliable memory-bit selection and recording in vortex-core cross-point architecture, specifically using a two-by-two vortex-state disk array. In order to efficiently switch a vortex core positioned at the intersection of crossed electrodes, two orthogonal addressing electrodes are selected, and then two Gaussian pulse currents of optimal pulse width and time delay are applied. Such tailored pulse-type rotating magnetic fields which occur only at the selected intersection are a prerequisite for a reliable memory-bit selection and low-power-consumption recording of information in the existing cross-point architecture.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials

Dependence of nonlocal Gilbert damping on the ferromagnetic layer type in ferromagnet/Cu/Pt heterostructures

A. Ghosh, J. F. Sierra, S. Auffret, U. Ebels, and W. E. Bailey

Appl. Phys. Lett. 98, 052508 (2011); http://dx.doi.org/10.1063/1.3551729 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2011

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We have measured the size effect in the nonlocal Gilbert relaxation rate in ferromagnet (FM) (tFM)/Cu(3 nm)[/Pt(2 nm)]/Al(3 nm) heterostructures, FM = {Ni81Fe19,Co60Fe20B20,pure Co}. A common behavior is observed for three FM layers where the additional relaxation obeys both a strict inverse power law dependence ΔG = Ktn, n = −1.04±0.06 and a similar magnitude K = 224±40 MHz⋅nm. As the tested FM layers span an order of magnitude in spin diffusion length λSD, the results are in support of spin diffusion rather than nonlocal resistivity as the origin of the effect.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Effect of vanadium deficiency on properties of polycrystalline LaVO3

S. Jamali Gharetape, M. P. Singh, F. S. Razavi, D. A. Crandles, L. Y. Zhao, and K. T. Leung

Appl. Phys. Lett. 98, 052509 (2011); http://dx.doi.org/10.1063/1.3549179 (3 pages)

Online Publication Date: 2 February 2011

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We report the influence of V deficiency on structure, transport, and magnetic properties of polycrystalline LaVO3. Up to 10% V-deficient samples were synthesized using standard solid state chemistry route. Structural and spectroscopic studies show that it intricately modifies lattice parameters and oxidation states of V. Further temperature dependent resistivity data reveal that V deficiency induces an enhancement in the resistivity and activation energy. The paramagnetic moment of these samples depends on net V composition while all samples exhibit a paramagnetic-to-antiferromagnetic transition at about 140 K. These distinct properties are understood owing to the presence of multiple oxidations states of V, predominantly V3+ and V4+, in nonstoichiometric LaVO3.
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61.66.Fn Inorganic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics

Direct observation of the spin configurations of vertical Bloch line

JinBae Kim, Hiro Akinaga, and Jongryoul Kim

Appl. Phys. Lett. 98, 052510 (2011); http://dx.doi.org/10.1063/1.3549694 (3 pages)

Online Publication Date: 2 February 2011

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We observed the spin configurations of Bloch lines in a ferromagnetic MnAs film on GaAs(001) by conventional magnetic force microscopy (MFM) and tilt-scanning (TS)-MFM. Due to the high lateral resolution of conventional MFM measurements, we were able to demonstrate the out-of-plane magnetic components within the Bloch line. Through vertical stray magnetic field mapping, the TS-MFM operation was shown to enable the detailed measurement and visualization of the spin configurations of the Bloch lines. This direct observation method of the spin configurations of vertical Bloch line structures allowed us to visualize antiparallel domain structure on the out-of-plane rotation of magnetization.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Magnetoresistance of Fe3O4-graphene-Fe3O4 junctions

Zhi-Min Liao, Han-Chun Wu, Jing-Jing Wang, Graham L. W. Cross, Shishir Kumar, Igor V. Shvets, and Georg S. Duesberg

Appl. Phys. Lett. 98, 052511 (2011); http://dx.doi.org/10.1063/1.3552679 (3 pages) | Cited 3 times

Online Publication Date: 3 February 2011

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The magnetoresistance (MR) of Fe3O4-graphene-Fe3O4 junctions has been experimentally studied at different temperatures. It is found that a barrier exists at the Fe3O4/graphene interface. The existence of the interfacial barrier was further confirmed by the nonlinear I-V characteristics and nonmetallic temperature dependence of the interfacial resistance. Moreover, spin dependent transport at the interfaces contributes −1.6% MR to the whole device at room temperature and can be regulated by an external electric field.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
75.76.+j Spin transport effects
72.25.-b Spin polarized transport
75.75.-c Magnetic properties of nanostructures
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