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6 Jul 2009

Volume 95, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 95, 013107 (2009); http://dx.doi.org/10.1063/1.3167775 (3 pages)

T. Y. Tsai, C. Y. Lee, N. H. Tai, and W. H. Tuan
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Search for transformation from paramagnetic martensite to ferromagnetic austenite: NiMnGaCu alloys

Chengbao Jiang, Jingmin Wang, Panpan Li, Ao Jia, and Huibin Xu

Appl. Phys. Lett. 95, 012501 (2009); http://dx.doi.org/10.1063/1.3155199 (3 pages) | Cited 9 times

Online Publication Date: 6 July 2009

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Search for transformation from paramagnetic martensite to ferromagnetic austenite in ferromagnetic shape memory alloys is performed through designing NiMnGaCu alloys. The composition dependence of the martensitic transformation temperature TM, the magnetic transition temperatures TCA of the austenite and TCM of the martensite is systematically investigated. The sequence of the martensitic transformation and magnetic transition is determined. The diagram on the structural and magnetic transition in a specific system Ni46Mn25+xGa25−xCu4 is outlined, in which a transformation from paramagnetic martensite to ferromagnetic austenite is predicted, exhibiting TCM<TM<TCA. Such a transformation is then experimentally achieved in Ni46Mn33Ga17Cu4 alloy.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys

Double magnetic tunnel junctions with cross-magnetization configurations for electrical detection of domain-wall structures

Tetsuya Uemura (植村哲也), Keisuke Sawada (澤田圭佑), Ken-ichi Matsuda (松田健一), and Masafumi Yamamoto (山本眞史)

Appl. Phys. Lett. 95, 012502 (2009); http://dx.doi.org/10.1063/1.3168514 (3 pages) | Cited 1 time

Online Publication Date: 7 July 2009

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A device consisting of double magnetic tunnel junctions with cross-magnetization configurations is proposed to enable simultaneous electrical detection of both the structure and motion of a domain-wall (DW). Operation of this device has been confirmed through micromagnetic simulation. Owing to the cross-magnetization configurations, two types of DW structure formed in a ferromagnetic wire were clearly identified: a transverse wall (TW) in which the magnetization at the center of the wall is directed transversely to the wire axis and a vortex wall (VW) in which the magnetization circulates in the plane around a small perpendicular vortex core. In addition to the structural difference between TW and VW, the velocity of the DW motion was detected through the time response of the tunneling magnetoresistance.
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75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure

Locally induced domain wall damping in a thin magnetic wire

G. Infante, R. Varga, G. A. Badini-Confalonieri, and M. Vázquez

Appl. Phys. Lett. 95, 012503 (2009); http://dx.doi.org/10.1063/1.3174919 (3 pages) | Cited 5 times

Online Publication Date: 8 July 2009

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The damping mechanisms affecting the motion of a single domain wall were studied in a thin bistable magnetic wire. It was found that the overall damping is frequency and temperature dependent through the locally induced anisotropy via structural relaxation. This phenomenon can increase the overall damping by one order of magnitude and enables an effective tailoring of the domain wall dynamics according to required application.
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75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy

Observation of microwave-assisted magnetization reversal in Fe65Co35 thin films through ferromagnetic resonance measurements

Corneliu Nistor, Ke Sun, Zihui Wang, Mingzhong Wu, Christoph Mathieu, and Matthew Hadley

Appl. Phys. Lett. 95, 012504 (2009); http://dx.doi.org/10.1063/1.3175721 (3 pages) | Cited 12 times

Online Publication Date: 8 July 2009

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This letter reports a new approach for microwave-assisted magnetization reversal (MAMR) measurements and the demonstration of MAMR in a Fe65Co35 thin film with this approach. The approach uses a microstrip line to deliver microwaves to and measure the ferromagnetic resonance (FMR) of the sample. The switching field is determined through the measurements of the FMR absorption as a function of static field. In the presence of microwaves, a reduction in switching field by 50% was observed in a Fe65Co35 film. This reduction was independent of the duration of microwave pulses. This indicates the reduction is not a heating effect.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys

Magnetotransport properties of p-type carbon-doped ZnO thin films

T. S. Herng, S. P. Lau, L. Wang, B. C. Zhao, S. F. Yu, M. Tanemura, A. Akaike, and K. S. Teng

Appl. Phys. Lett. 95, 012505 (2009); http://dx.doi.org/10.1063/1.3176434 (3 pages) | Cited 34 times

Online Publication Date: 8 July 2009

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Carbon-doped ZnO (ZnO:C) thin films exhibiting Curie temperature above room temperature were fabricated using ion beam technique. The magnetic moment of the ZnO:C films was found to be around 1.35 μB per carbon atom. The ZnO:C films showed p-type conduction with a hole concentration of ∼ 5×1017 cm−3. In addition, the anomalous Hall effect and negative magnetoresistance can be detected in the ZnO:C films. The magnetotransport properties of the ZnO:C suggested that the films possessed charge carrier spin polarization.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
72.25.Dc Spin polarized transport in semiconductors
73.61.Ga II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Ultrafast switching of a nanomagnet by a combined out-of-plane and in-plane polarized spin current pulse

O. J. Lee, V. S. Pribiag, P. M. Braganca, P. G. Gowtham, D. C. Ralph, and R. A. Buhrman

Appl. Phys. Lett. 95, 012506 (2009); http://dx.doi.org/10.1063/1.3176938 (3 pages) | Cited 19 times

Online Publication Date: 8 July 2009

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We report on spin valve devices that incorporate both an out-of-plane polarizer (OPP) to quickly excite spin torque (ST) switching and an in-plane polarizer/analyzer (IPP). For pulses <200 ps, we observe reliable precessional switching due largely to ST from the OPP. Compared to a conventional spin valve, for a given current amplitude from ∼ 2 to 3 times the zero-thermal-fluctuation critical current (Ic0), the addition of the OPP can decrease the pulse width necessary for switching by a factor of 10 or more. The effect of the IPP also has beneficial ST consequences for the short pulse switching behavior.
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72.25.-b Spin polarized transport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.-d Domain effects, magnetization curves, and hysteresis

Time-resolved zero field vortex oscillations in point contacts

T. Devolder, Joo-Von Kim, P. Crozat, C. Chappert, M. Manfrini, M. van Kampen, W. Van Roy, L. Lagae, G. Hrkac, and T. Schrefl

Appl. Phys. Lett. 95, 012507 (2009); http://dx.doi.org/10.1063/1.3170234 (3 pages) | Cited 13 times

Online Publication Date: 9 July 2009

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We study vortex spin torque oscillators based on magnetic point contacts that operate in zero applied magnetic field. Static and dynamic vortex modes are shown to exist and have distinct electrical signatures. For the oscillatory mode, a spectrally pure slightly asymmetric voltage waveform is observed. It is subject to phase noise as sole fluctuations. The waveforms observed indicate that the vortex orbits outside the point contact region, with a pinned layer magnetization that is static but spatially nonuniform as a result of the current. This nonuniformity results in a reduction in the dc to rf power transduction yield.
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75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Role of the electronic structure on the relationship between the crystallinity of CoFe and its tunneling magnetoresistance

Li Gao, Xin Jiang, D. M. C. Nicholson, Teya Topuria, and Stuart S. P. Parkin

Appl. Phys. Lett. 95, 012508 (2009); http://dx.doi.org/10.1063/1.3132084 (3 pages) | Cited 1 time

Online Publication Date: 10 July 2009

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The influence of the crystallinity of CoFe on tunneling magnetoresistance is investigated in magnetic tunnel junctions with an amorphous Al2O3 tunnel barrier. An enhancement in the tunneling magnetoresistance is found when the CoFe is made amorphous compared to when it is crystalline. Ab initio electronic structure calculations show substantial differences in the band structures of crystalline and amorphous forms of bulk CoFe alloys but a decreased spin polarization at the Fermi energy in the amorphous phase. We speculate that the increased tunneling magnetoresistance is rather due to changes in bonding at the interface between Al2O3 and CoFe.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Kj Amorphous and quasicrystalline magnetic materials
71.20.Be Transition metals and alloys
71.23.-k Electronic structure of disordered solids
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys

First-principles study on ferromagnetism in nitrogen-doped In2O3

L. X. Guan, J. G. Tao, C. H. A. Huan, J. L. Kuo, and L. Wang

Appl. Phys. Lett. 95, 012509 (2009); http://dx.doi.org/10.1063/1.3176410 (3 pages) | Cited 20 times

Online Publication Date: 10 July 2009

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We report stable room temperature ferromagnetism in nitrogen doped In2O3 (N–In2O3) based on density functional theory. Our investigation on the electronic and magnetic properties of N–In2O3 suggests that N dopant introduces spin-polarized hole states in the band gap generating a total magnetic moment of 1.0μB per N, which is mainly localized on the doped N atoms. The ferromagnetic interaction in N–In2O3 system is mainly driven by the occurrence of coupling chains between a first N (N1)-2p to a second N (N2)-2p via a bridging In 5p and 4d orbitals.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.up Other materials
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
71.20.Nr Semiconductor compounds

Direct evidence of imprinted vortex states in the antiferromagnet of exchange biased microdisks

G. Salazar-Alvarez, J. J. Kavich, J. Sort, A. Mugarza, S. Stepanow, A. Potenza, H. Marchetto, S. S. Dhesi, V. Baltz, B. Dieny, A. Weber, L. J. Heyderman, J. Nogués, and P. Gambardella

Appl. Phys. Lett. 95, 012510 (2009); http://dx.doi.org/10.1063/1.3168515 (3 pages) | Cited 1 time

Online Publication Date: 10 July 2009

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See Also: Publisher's Note

Show Abstract
The magnetic domain structure of patterned antiferromagnetic/ferromagnetic Ir20Mn80/Ni80Fe20 bilayer microdisk arrays has been investigated using layer-specific polarized x-ray photoemission electron microscopy and magnetic circular dichroism. Magnetic imaging at the Fe and Mn L-edge resonances provided direct evidence of a vortex state imprinted into the antiferromagnet at the interface. The opposite magnetic contrast between the layers indicated a reversed chirality of the imprinted vortex state, and a quantitative analysis of the magnetic moment from the dichroism spectra showed that uncompensated Mn spins equivalent to about 60% of a monolayer of bulk Ir20Mn80 contributed to the imprinted information at the interface.
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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.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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