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14 Jun 2004

Volume 84, Issue 24, pp. 4839-5046

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4409 (2004); http://dx.doi.org/10.1063/1.1757648 (3 pages)

Azita Soleymani, Piroz Zamankhan, and William Polashenski
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Size effects on exchange bias in sub-100 nm ferromagnetic–antiferromagnetic dots deposited on prepatterned substrates

V. Baltz, J. Sort, B. Rodmacq, B. Dieny, and S. Landis

Appl. Phys. Lett. 84, 4923 (2004); http://dx.doi.org/10.1063/1.1757646 (3 pages) | Cited 16 times

Online Publication Date: 28 May 2004

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Exchange bias effects have been investigated in ferromagnetic (FM)–antiferromagnetic (AFM) square dots, with lateral sizes of 90 nm, sputtered on a prepatterned Si substrate. The magnetic behavior of the dots has been compared with that of a continuous FM–AFM bilayer with the same composition. Along the unidirectional direction, the dots exhibit square hysteresis loops and preserve an exchange bias field, HE, of 70 Oe at room temperature, which is about 40% smaller than HE in the continuous film. In addition, the distribution of blocking temperatures in the nanostructures is found to be shifted toward lower values with respect to that in the continuous film. These results can be interpreted assuming that the reduced lateral dimensions of the nanostructures impose some constraints on the formation and pinning of domain walls in the AFM layer. © 2004 American Institute of Physics.
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75.50.Ee Antiferromagnetics
61.46.-w Structure of nanoscale materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Direct observation of the barrier asymmetry in magnetic tunnel junctions

P. H. P. Koller, H. J. M. Swagten, W. J. M. de Jonge, H. Boeve, and R. Coehoorn

Appl. Phys. Lett. 84, 4929 (2004); http://dx.doi.org/10.1063/1.1759778 (3 pages) | Cited 8 times

Online Publication Date: 28 May 2004

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A photoconductance method has been used to study directly the barrier asymmetry in TaOx magnetic tunnel junctions. Due to optical electron-hole pair generation in the barrier itself and subsequent transport in the electric field, the sign and magnitude of the barrier asymmetry can be determined quite accurately. The reliability of the technique is demonstrated by the independence on the direction of illumination. The oxidation time where the asymmetry becomes zero is found to coincide with a maximum in the magnetoresistance ratio. This is argued to be due to the complete oxidation of the barrier material, resulting in a symmetric tunnel barrier. © 2004 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.65.Mq Oxidation

Noncollinear magnetism and enhancement of magnetocrystalline anisotropy at the Σ3(111) grain boundary in ferromagnetic Fe

Kohji Nakamura, Tomonori Ito, A. J. Freeman, Lieping Zhong, and Juan Fernandez-de-Castro

Appl. Phys. Lett. 84, 4974 (2004); http://dx.doi.org/10.1063/1.1762976 (3 pages)

Online Publication Date: 28 May 2004

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Magnetic structures and magnetocrystalline anisotropy of the Σ3[1math0](111) grain boundary (GB) in ferromagnetic Fe are investigated by the first-principles full-potential linearized augmented plane-wave method including intra-atomic noncollinear magnetism. In breaking the spatial translation symmetry in a crystalline solid, the GB is found to give rise to a magnetic noncollinearity, where the magnetic moments at both sides of the GB orient at an angle of about 10° with respect to each other. Importantly, the presence of the GB enhances the magnetocrystalline anisotropy energy by one order of magnitude from its bulk value and may induce a pinning effect on the magnetization rotation or magnetic domain wall motion. © 2004 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
61.72.Mm Grain and twin boundaries
75.50.Bb Fe and its alloys
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ch Domain walls and domain structure

Microwave generation by a direct current spin-polarized current in nanoscale square magnets

Haiwen Xi, Kai-Zhong Gao, and Yiming Shi

Appl. Phys. Lett. 84, 4977 (2004); http://dx.doi.org/10.1063/1.1762981 (3 pages) | Cited 13 times

Online Publication Date: 28 May 2004

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Theoretical calculation for a simple nanoscale magnetoelectronic device to function as a microwave generator based on the spin-transfer torque effect is presented. The device is unique because the output amplitude and frequency can be continuously tuned by the electrical current in the microwave frequency range. Analysis and discussion of the device structure, function, and realization are provided. © 2004 American Institute of Physics.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.30.Gw Magnetic anisotropy
85.35.-p Nanoelectronic devices
72.25.-b Spin polarized transport

Position noise in scanning superconducting quantum interference device microscopy

Su-Young Lee, J. Matthews, and F. C. Wellstood

Appl. Phys. Lett. 84, 5001 (2004); http://dx.doi.org/10.1063/1.1763215 (3 pages) | Cited 5 times

Online Publication Date: 28 May 2004

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Experimentally obtained magnetic field images contain not only magnetic field noise, but also uncertainty in the position at which the data points are recorded. Such position noise degrades the images where the magnetic field gradients are strongest. Our high-Tc scanning superconducting quantum interference device (SQUID) microscope was found to be limited by a position noise of about 0.145 μm. For a straight wire carrying 500 μA with a rms magnetic noise of 0.185 nT, and source–sample separation 150 μm, we find that the rms position noise must be less than 62 nm for it to have less impact on the image quality than intrinsic magnetic SQUID noise. © 2004 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.72.-h Cuprate superconductors
07.55.-w Magnetic instruments and components

High Curie temperatures in ferromagnetic Cr-doped AlN thin films

D. Kumar, J. Antifakos, M. G. Blamire, and Z. H. Barber

Appl. Phys. Lett. 84, 5004 (2004); http://dx.doi.org/10.1063/1.1763216 (3 pages) | Cited 60 times

Online Publication Date: 28 May 2004

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Al1−xCrxN thin films with 0.02⩽x⩽0.1 were deposited by reactive co-sputtering onto c-plane (001) sapphire. Room-temperature ferromagnetism with a coercive field of 85 Oe was observed in samples with chromium contents as low as x = 0.027 (2.7%). With increasing Cr content the mean magnetic moment is strongly suppressed, with a maximum saturation moment of 0.62 and 0.71 μB per Cr atom at 300 and 50 K, respectively. We show that the Curie temperature of Al1−xCrxN for x = 0.027 is greater than 900 K. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
81.15.Cd Deposition by sputtering

Positive colossal magnetoresistance in a multilayer p–n heterostructure of Sr-doped LaMnO3 and Nb-doped SrTiO3

H. B. Lu, G. Z. Yang, Z. H. Chen, S. Y. Dai, Y. L. Zhou, K. J. Jin, B. L. Cheng, M. He, L. F. Liu, H. Z. Guo, Y. Y. Fei, W. F. Xiang, and L. Yan

Appl. Phys. Lett. 84, 5007 (2004); http://dx.doi.org/10.1063/1.1763217 (3 pages) | Cited 43 times

Online Publication Date: 28 May 2004

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A positive colossal magnetoresistance (CMR) has been discovered in an epitaxial multilayer p–n heterostructure fabricated with Sr-doped LaMnO3 and Nb-doped SrTiO3 by laser molecular-beam epitaxy. In contrast to the negative CMR of the LaMnO3 compound family, positive CMR is observed in the temperature range from 100 to 300 K. The largest value of the magnetoresistance (MR) ratio (ΔR/R0,ΔR = RH−R0), 517%, is one order of magnitude larger than that of simple p–n junctions of the same materials previously reported. A very large MR ratio, 297%, remains in a low field of 0.01 T. Even at a temperature as high as 300 K, a MR ratio as large as 17.3% is still observed. © 2004 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

SrFeO3 nanoparticles-dispersed SrMoO4 insulating thin films deposited from Sr2FeMoO6 target in oxygen atmosphere

Dal-Young Kim, Jin Soo Kim, Bae Ho Park, Jeon-Kook Lee, Jang Hee Kim, Je Hyun Lee, Joonyeon Chang, Hi-Jung Kim, Inyoung Kim, and Yun D. Park

Appl. Phys. Lett. 84, 5037 (2004); http://dx.doi.org/10.1063/1.1763638 (3 pages) | Cited 4 times

Online Publication Date: 28 May 2004

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Dielectric SrMoO4 thin films were deposited from Sr2FeMoO6 target in oxygen atmosphere, showing obvious M–H hysteresis loops at room temperature. It was revealed by transmission electron microscopy that SrFeO3 nanoparticles are dispersed in the SrMoO4 grains, to which the hystersis loops of the thin films are ascribed. This SrMoO4 thin film can be useful as a barrier material for Sr2FeMoO6-based devices, owing to easy fabrication process and compatibility with Sr2FeMoO6. Magnetic SrFeO3 nanoparticles are expected to enhance tunneling magnetoresistance. © 2004 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.37.Lp Transmission electron microscopy (TEM)
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