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20 Apr 2009

Volume 94, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 94, 161105 (2009); http://dx.doi.org/10.1063/1.3119666 (3 pages)

Artur R. Davoyan, Ilya V. Shadrivov, Andrey A. Sukhorukov, and Yuri S. Kivshar
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Probing the magnetic state of Fe/FeO/Fe trilayers by multiple isotopic sensor layers

S. Couet, Th. Diederich, S. Stankov, K. Schlage, T. Slezak, R. Rüffer, J. Korecki, and R. Röhlsberger

Appl. Phys. Lett. 94, 162501 (2009); http://dx.doi.org/10.1063/1.3120770 (3 pages) | Cited 5 times

Online Publication Date: 20 April 2009

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To obtain depth-selected information in magnetic multilayers, we propose a measurement scheme based on nuclear resonant scattering from multiple isotopic sensor layers. It takes advantage of the depth dependence of the photon wavefield intensity in grazing incidence geometry to enhance the signal from a given part of a multilayer. The technique is applied to study the magnetic structure of a Fe/Fe-oxide/Fe trilayer. We are able to fully determine in a direct manner the magnetic state of two ultrathin 57Fe probe layers embedded in the system. The proposed technique can potentially be extended to various grazing incidence x-ray scattering methods.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
78.70.Ck X-ray scattering

Greatly enhanced azimuthal permeability of a ferrite core with a wire coil metamaterial

Z. W. Li, R. F. Huang, and L. B. Kong

Appl. Phys. Lett. 94, 162502 (2009); http://dx.doi.org/10.1063/1.3122942 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2009

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Metamaterial has been developed using a structure of Cu-wire coil wound on a ferrite core. The metamaterial has greatly enhanced azimuthal permeability, as compared to the mere core material, and its resonance frequency can be controlled through varying the number of turns of the coil. These special properties, which are significantly different from general magnetic material, can be understood by an equivalent lumped parameter model.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.32.Hh Inductors and coils; wiring
75.50.Gg Ferrimagnetics
42.70.-a Optical materials

Surface magnetization in non-doped ZnO nanostructures

A. L. Schoenhalz, J. T. Arantes, A. Fazzio, and G. M. Dalpian

Appl. Phys. Lett. 94, 162503 (2009); http://dx.doi.org/10.1063/1.3119640 (3 pages) | Cited 24 times

Online Publication Date: 20 April 2009

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We have investigated the magnetic properties of non-doped ZnO nanostructures by using ab initio total energy calculations. Contrary to many proposals that ferromagnetism in non-doped semiconductors should be induced by intrinsic point defects, we show that ferromagnetism in nanostructured materials should be mediated by extended defects such as surfaces and grain boundaries. This kind of defects creates delocalized, spin-polarized states that should be able to warrant long-range magnetic interactions.
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75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
71.15.Nc Total energy and cohesive energy calculations
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Mm Grain and twin boundaries
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Improved tunnel magnetoresistance of magnetic tunnel junctions with Heusler Co2FeAl0.5Si0.5 electrodes fabricated by molecular beam epitaxy

N. Tezuka, N. Ikeda, F. Mitsuhashi, and S. Sugimoto

Appl. Phys. Lett. 94, 162504 (2009); http://dx.doi.org/10.1063/1.3116717 (3 pages) | Cited 61 times

Online Publication Date: 21 April 2009

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The authors have developed a magnetic tunnel junction of Co2FeAl0.5Si0.5 electrodes and a MgO barrier fabricated by molecular beam epitaxy and observed that this device had a tunnel magnetoresistance ratio of 386% at approximately 300 K and 832% at 9 K. The lower Co2FeAl0.5Si0.5 electrode was annealed during and after deposition resulting in a highly ordered structure with small roughness. This highly ordered structure could be obtained by annealing treatment even at low temperatures. Furthermore, a weak temperature dependence of the tunnel magnetoresistance ratio was observed for the developed magnetic tunnel junction.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Ac Multilayers
81.40.Gh Other heat and thermomechanical treatments

Ferromagnetism of undoped GaN mediated by through-bond spin polarization between nitrogen dangling bonds

Hao Jin, Ying Dai, BaiBiao Huang, and M.-H. Whangbo

Appl. Phys. Lett. 94, 162505 (2009); http://dx.doi.org/10.1063/1.3123169 (3 pages) | Cited 31 times

Online Publication Date: 22 April 2009

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Room-temperature ferromagnetism occurs in GaN nanoparticles even without any doped magnetic ions. The cause for this finding was examined by performing density functional calculations for the bulk GaN and the nonpolar surface of GaN with Ga- and N-vacancies. Our work indicates that the room-temperature ferromagnetism of undoped GaN nanoparticles originates from the nitrogen dangling bonds associated with the surface Ga-vacancies. The spins of the nitrogen dangling bonds couple ferromagnetically by through-bond spin polarization, and this ferromagnetic coupling is effective even when the vacancy separation is as long as ∼ 8 Å.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jd Vacancies

Enhancement of the magnetic field sensitivity in Al2O3 encapsulated NiFe films with anisotropic magnetoresistance

Lei Ding, Jiao Teng, Qian Zhan, Chun Feng, Ming-hua Li, Gang Han, Li-jin Wang, Guang-hua Yu, and Shu-yun Wang

Appl. Phys. Lett. 94, 162506 (2009); http://dx.doi.org/10.1063/1.3123807 (3 pages) | Cited 8 times

Online Publication Date: 23 April 2009

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The anisotropic magnetoresistance value (ΔR/R) and magnetic field sensitivity (Sv) of NiFe films can be remarkably enhanced by using Al2O3 encapsulation, and the Sv is comparable to that of a spin valve. For an ultrathin NiFe film with the structure of Ta/Al2O3/NiFe/Al2O3/Ta, the Al2O3 layers suppress the formation of the magnetic dead layers and the interdiffusions between the NiFe layer and Ta layers, and decrease the current shunting of the Ta layers. More importantly, the flatter Al2O3/NiFe and NiFe/Al2O3 interfaces can significantly enhance the specular reflection of conduction electrons and lead to a higher ΔR/R. In addition, the formations of the NiFe (111) texture and the columnar grains by annealing can also increase the ΔR/R.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
68.55.jm Texture

Submicron-scale spatial feature of ultrafast photoinduced magnetization reversal in TbFeCo thin film

T. Ogasawara, N. Iwata, Y. Murakami, H. Okamoto, and Y. Tokura

Appl. Phys. Lett. 94, 162507 (2009); http://dx.doi.org/10.1063/1.3123256 (3 pages) | Cited 13 times

Online Publication Date: 24 April 2009

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Submicron-scale spatial feature of magnetization reversal dynamics induced by femtosecond optical pulse irradiation in a small external magnetic field was investigated by time-resolved magneto-optical Kerr microscopy on TbFeCo thin film. The magnetization reversal time near the magnetic domain boundary is dominated by an effective magnetic field generated from the peripheral domain by dipole-dipole interaction. The magnetization reversal is accelerated as high as 4.5 times (from 3.4 ns to 750 ps) when reducing the reversed domain size from 1.5 to 0.4 μm due to concentration of dipole-dipole interaction.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.47.D- Time resolved spectroscopy (>1 psec)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
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