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28 Feb 2011

Volume 98, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 98, 093502 (2011); http://dx.doi.org/10.1063/1.3531756 (3 pages)

Marina S. Leite, Robyn L. Woo, William D. Hong, Daniel C. Law, and Harry A. Atwater
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Effect of nonadiabatic spin transfer torque on domain wall resonance frequency and mass

Mahdi Jamali, Kyung-Jin Lee, and Hyunsoo Yang

Appl. Phys. Lett. 98, 092501 (2011); http://dx.doi.org/10.1063/1.3560305 (3 pages) | Cited 4 times

Online Publication Date: 28 February 2011

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The dynamics of a magnetic domain wall in a semi circular nanowire loop is studied by an analytical model and micromagnetic simulations. We find a damped sinusoidal oscillation of the domain wall for small displacement angles around its equilibrium position under an external magnetic field in the absence of currents. By studying the effect of current induced nonadiabatic spin transfer torque on the magnetic domain wall resonance frequency and mass, a redshift is found in the resonance frequency and domain wall mass increases by increasing the ratio of nonadiabatic spin torque to adiabatic contribution above 1.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys

Probing dipole coupled nanomagnets using magnetoresistance read

Andrew Lyle, Angeline Klemm, Jonathan Harms, Yisong Zhang, Hui Zhao, and Jian-Ping Wang

Appl. Phys. Lett. 98, 092502 (2011); http://dx.doi.org/10.1063/1.3558915 (3 pages) | Cited 6 times

Online Publication Date: 28 February 2011

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We experimentally demonstrated magnetoresistance (MR) read of dipole coupled nanomagnets using magnetic tunnel junctions. The MR allowed the magnetic state of individual nanomagnets to be electrically measured. The sensitivity of the read scheme enabled a systematic study regarding the nanomagnet spacing and revealed a transition in behavior. Below a spacing of 15 nm the dipole field overcomes the individual shape anisotropy and redefines the individual element easy axis along the direction transmission line. The demonstration of MR electrical read marks a significant step forward for applications such as magnetic quantum cellular automata logic devices.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.De Giant magnetoresistance
75.75.-c Magnetic properties of nanostructures

Competing effects of magnetocrystalline anisotropy and exchange bias in epitaxial Fe/IrMn bilayers

Wei Zhang, Mark E. Bowden, and Kannan M. Krishnan

Appl. Phys. Lett. 98, 092503 (2011); http://dx.doi.org/10.1063/1.3561516 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2011

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We systematically investigated the possible magnetization reversal behavior in well-characterized, epitaxial, Fe/IrMn exchange-biased bilayers as a function of the antiferromagnetic (AF) layer thickness. Several kinds of multistep loops were observed for the samples measured at various field orientations. The angular dependence of the switching fields, observed using longitudinal and transverse magneto-optic Kerr effect, were shown to depend on the competition between the magnetocrystalline anisotropy and the exchange bias (EB). A modified “effective field” model was applied to quantitatively describe the evolution of the magnetic behavior and correctly predict the occurrence of different magnetic switching processes. The dependence of the effective anisotropy fields on the AF layer thickness directly reflects the competing effects of the pinned and rotatable AF spins at the EB interface.
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75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics

Detection of single magnetic nanobead with a nano-superconducting quantum interference device

L. Hao, C. Aßmann, J. C. Gallop, D. Cox, F. Ruede, O. Kazakova, P. Josephs-Franks, D. Drung, and Th. Schurig

Appl. Phys. Lett. 98, 092504 (2011); http://dx.doi.org/10.1063/1.3561743 (3 pages) | Cited 9 times

Online Publication Date: 1 March 2011

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We report the use of an ultralow noise nano-superconducting quantum interference device (nanoSQUID) to measure the hysteretic magnetization behavior of a single FePt nanobead at a temperature of around 7 K in a magnetic field of only ∼ 10 mT. We also show that the nanobead can be accurately positioned with respect to the SQUID loop and then removed without affecting SQUID performance. This system is capable of further development with wide applications in nanomagnetism.
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75.75.Jn Dynamics of magnetic nanoparticles
75.78.-n Magnetization dynamics
75.50.Tt Fine-particle systems; nanocrystalline materials

Electric field control of magnetic anisotropies and magnetic coercivity in Fe/BaTiO3(001) heterostructures

S. Brivio, D. Petti, R. Bertacco, and J. C. Cezar

Appl. Phys. Lett. 98, 092505 (2011); http://dx.doi.org/10.1063/1.3554432 (3 pages) | Cited 11 times

Online Publication Date: 1 March 2011

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Magnetoelectric effects in Fe/BaTiO3(001) heterostructures have been investigated via magneto-optical Kerr effect as a function of temperature. We find major modifications of magnetic anisotropies and magnetic coercivity induced by the application of electric fields perpendicular to the interface. Changes in the coercive magnetic field, on the order of 100% at 250 K (in the orthorhombic phase of BaTiO3) and 40% at 300 K (in the tetragonal phase), which are linked to the ferroelectric behavior of BaTiO3, are reported.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.85.+t Magnetoelectric effects, multiferroics

N site ordering effect on partially ordered Fe16N2

Nian Ji, Lawrence F. Allard, Edgar Lara-Curzio, and Jian-Ping Wang

Appl. Phys. Lett. 98, 092506 (2011); http://dx.doi.org/10.1063/1.3560051 (3 pages) | Cited 1 time

Online Publication Date: 1 March 2011

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Partially ordered Fe16N2 thin films have been fabricated on Fe (001)-buffered GaAs (001) single-crystal substrates by a facing target sputtering process. The saturation magnetization has been systematically investigated as a function of N site ordering in partially ordered Fe16N2 thin films, which is found to be increased monotonically with the increase in the N site ordering parameter, reaching up to 2.68 T at high ordering case. A model discussion is provided based on the partial localization of 3d electron states in this material system, which successfully rationalizes the formation of the giant saturation magnetization in chemically ordered Fe16N2. We further demonstrate that the average magnetic moment of partially ordered Fe16N2 sensitively depends on the special arrangement of Fe6N clusters, which is the key to realize high magnetic moment in this material system.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

AlNxMn3: A possible high-temperature soft magnetic material and strongly correlated system

J. C. Lin, B. S. Wang, P. Tong, W. J. Lu, L. Zhang, X. B. Zhu, Z. R. Yang, W. H. Song, J. M. Dai, and Y. P. Sun

Appl. Phys. Lett. 98, 092507 (2011); http://dx.doi.org/10.1063/1.3562315 (3 pages) | Cited 3 times

Online Publication Date: 2 March 2011

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Structural, magnetic, electrical, and thermal transport properties of antiperovskite compounds AlNxMn3 (x = 1,1.1,1.2) have been investigated systematically. With increasing x, the lattice constant increases monotonously while the Curie temperature TC decreases. Both the high TC and small coercive fields consistently indicate AlNxMn3 may be a promising high-temperature soft magnetic material. The resistivity displays T2-dependence below 30 K and the Kadowaki–Woods ratio is about 107.7 μΩ cm/K2, indicating a possible strongly correlated Fermi-liquid behavior in AlNMn3. Further analysis suggests that the electron-type carriers are dominant and the thermal conductivity mainly originates from the lattice contribution.
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61.66.Fn Inorganic compounds
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
72.20.Pa Thermoelectric and thermomagnetic effects

Hydrothermal growth of single crystals of the quantum magnets: Clinoatacamite, paratacamite, and herbertsmithite

Shaoyan Chu, Peter Müller, Daniel G. Nocera, and Young S. Lee

Appl. Phys. Lett. 98, 092508 (2011); http://dx.doi.org/10.1063/1.3562010 (3 pages)

Online Publication Date: 3 March 2011

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We present a hydrothermal method for growing millimeter-sized crystals of the quantum magnets with formula Cu4−xZnx(OH)6Cl2: clinoatacamite (x = 0), paratacamite (0.33<x<1) and herbertsmithite (x = 1). These highly pure single crystals have been characterized by x-ray diffraction, chemical analysis, Raman spectroscopy, and magnetic susceptibility measurements. This synthesis success opens the door for detailed investigations of the magnetic ground-state properties of these compounds.
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81.10.Dn Growth from solutions
75.30.Cr Saturation moments and magnetic susceptibilities
61.66.Fn Inorganic compounds
78.30.Hv Other nonmetallic inorganics

Ultrafast magnetization relaxation of L10-ordered Fe50Pt50 alloy thin film

Ji-Wan Kim, Hyon-Seok Song, Jae-Woo Jeong, Kyeong-Dong Lee, Jeong-Woo Sohn, Toshiyuki Shima, and Sung-Chul Shin

Appl. Phys. Lett. 98, 092509 (2011); http://dx.doi.org/10.1063/1.3559845 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2011

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We have investigated the ultrafast magnetization dynamics of L10-ordered Fe50Pt50 thin film by means of a time-resolved magneto-optical Kerr effect measurement. We have found a high Gilbert damping value of α ∼ 0.26, together with a very high precession frequency of f ∼ 85 GHz and the shortest relaxation characteristic time of τ ∼ 6.5 ps ever reported. We believe that L10-ordered FePt film with the unique property of a very high precession frequency and the shortest relaxation time will be very useful for the realization of picosecond spin switching.
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75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.78.Jp Ultrafast magnetization dynamics and switching
75.60.-d Domain effects, magnetization curves, and hysteresis

Evidence of defect-induced ferromagnetism and its “switch” action in pristine bulk TiO2

R. K. Singhal, Sudhish Kumar, P. Kumari, Y. T. Xing, and E. Saitovitch

Appl. Phys. Lett. 98, 092510 (2011); http://dx.doi.org/10.1063/1.3562328 (3 pages) | Cited 15 times

Online Publication Date: 3 March 2011

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In this work, we demonstrate that room temperature ferromagnetism can be induced in pristine anatase TiO2 paramagnetic bulk powder through extended hydrogenation. Defect complexes, Ti3+–VO (Ti3+ ions accompanied by oxygen vacancies) are clearly identified in hydrogenated TiO2 by combining x-ray diffraction and photoemission spectroscopy. The observed ferromagnetic ordering is reversible that can be switched between “on” and “off” by inducing or removing, respectively, these defect complex. We convincingly elucidate that the factors (i) Ti 3d–O 2p hybridization (iii) F+ centers (the electrons in singly occupied oxygen vacancies), and (iii) oxygen vacancy assisted fragmentation of grains, compositely contribute to the ferromagnetic ordering.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.jn Color centers
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.jd Vacancies
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
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