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16 Oct 2006

Volume 89, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 89, 164101 (2006); http://dx.doi.org/10.1063/1.2362602 (3 pages)

Yen-Wen Lu and Chang-Jin(CJ) Kim
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Influence of annealing on the bias voltage dependence of tunneling magnetoresistance in MgO double-barrier magnetic tunnel junctions with CoFeB electrodes

Gen Feng, Sebastiaan van Dijken, and J. M. D. Coey

Appl. Phys. Lett. 89, 162501 (2006); http://dx.doi.org/10.1063/1.2362977 (3 pages) | Cited 18 times

Online Publication Date: 16 October 2006

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Double-barrier magnetic tunnel junctions with two MgO barriers and three CoFeB layers exhibiting tunneling magnetoresistance (TMR) values of more than 100% were fabricated. The bias voltage dependence of the TMR ratio is highly asymmetric after annealing at low temperatures, indicating dissimilar CoFeB/MgO interfaces. The TMR effect decays very slowly for positive bias and is only reduced to half of its maximum value at V1/2 = 1.88 V when the junctions are processed at 200 °C. The largest output voltage, 0.62 V, is obtained after annealing at 300 °C, a temperature that combines high TMR ratios with a considerable asymmetric bias dependence.
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75.47.Pq Other materials
81.40.Gh Other heat and thermomechanical treatments
75.50.Dd Nonmetallic ferromagnetic materials

Magnetic glassy phase in Zn0.85Fe0.15O diluted magnetic semiconducting nanoparticles

S. K. Mandal, T. K. Nath, A. Das, and R. K. Kremer

Appl. Phys. Lett. 89, 162502 (2006); http://dx.doi.org/10.1063/1.2363140 (3 pages) | Cited 12 times

Online Publication Date: 16 October 2006

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The authors have investigated the ground state magnetic phase and the optical band gap of chemically synthesized Zn0.85Fe0.15O diluted magnetic semiconducting nanoparticles ( ∼ 7.5 nm). The temperature dependent magnetization study shows strong irreversibility along with a cusplike anomaly, which is ascribed to a freezing to a cluster glasslike magnetic ground state. This assignment is further established by Arrott-Belov-Kouvel plots along with S-like nonsaturating magnetization versus field curves. The finite size ferromagnetic clusters which are formed due to an enhanced grain surface effect in the system undergo random dipolar intercluster interactions, giving rise to strong competitive ferromagnetic and antiferromagnetic interactions, finally leading to the freezing of those clusters.
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75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Large magnetoresistance in single-crystalline Ni50Mn50−xInx alloys (x = 14–16) upon martensitic transformation

S. Y. Yu, Z. H. Liu, G. D. Liu, J. L. Chen, Z. X. Cao, G. H. Wu, B. Zhang, and X. X. Zhang

Appl. Phys. Lett. 89, 162503 (2006); http://dx.doi.org/10.1063/1.2362581 (3 pages) | Cited 89 times

Online Publication Date: 17 October 2006

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Variation of electrical resistance in single-crystalline Ni50Mn50−xInx alloys (x = 14–16) upon martensitic transformation was investigated. In Ni50Mn35In15 with Tm ∼ 295 K, a negative magnetoresistance (MR) over 60% is attainable at moderate field strengths; in Ni50Mn34In16 with Tm ∼ 190 K, the MR can exceed 70% over a temperature of approximately 100 K. The significant change in electric resistance upon martensitic transformation originates primarily from the altered electronic structure, while the large effect of a magnetic field follows its ability to manipulate the transformation in materials of low Tm and large ΔM/ΔS. The extremely large MR promises more innovative applications for these important alloys.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
71.20.Be Transition metals and alloys

Grain size reduction in CoCrPt:SiO2 perpendicular recording media with oxide-based intermediate layers

S. N. Piramanayagam, C. K. Pock, L. Lu, C. Y. Ong, J. Z. Shi, and C. S. Mah

Appl. Phys. Lett. 89, 162504 (2006); http://dx.doi.org/10.1063/1.2362643 (3 pages) | Cited 24 times

Online Publication Date: 17 October 2006

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CoCrPt–SiO2 perpendicular recording media containing an oxide-based intermediate layer have been studied in order to minimize the grain size in the recording layer. A RuCr alloy thin film deposited in an argon and oxygen reactive atmosphere was found to produce finer grains in the intermediate layer. When the recording layer was deposited on such an intermediate layer, the grain size of the recording layer was also observed to be smaller (about 6.4 nm center-to-center distances). The results indicate that the introduction of RuCr-oxide-based intermediate layers is a possible approach to reduce the grain size in perpendicular recording media.
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75.50.Ss Magnetic recording materials

Electric-field control of ferromagnetism in (Ga,Mn)As

D. Chiba, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 89, 162505 (2006); http://dx.doi.org/10.1063/1.2362971 (3 pages) | Cited 44 times

Online Publication Date: 17 October 2006

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The authors show modulation of Curie temperature TC and coercivity μ0Hc by applying external electric fields E in a ferromagnetic semiconductor (Ga,Mn)As, where a field-effect transistor structure with an Al2O3 gate insulator is utilized. Application of E = +5 (–5) MV/cm decreases (increases) TC of the channel layer. μ0Hc also decreases (increases) with increasing (decreasing) E below TC. The mechanism of the modulation of μ0Hc by E is discussed.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Large tunnel magnetoresistance in tunnel junctions with Co2MnSi/Co2FeSi multilayer electrode

D. Ebke, J. Schmalhorst, N.-N. Liu, A. Thomas, G. Reiss, and A. Hütten

Appl. Phys. Lett. 89, 162506 (2006); http://dx.doi.org/10.1063/1.2363939 (3 pages) | Cited 25 times

Online Publication Date: 17 October 2006

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Two kinds of magnetic tunnel junctions with Co2FeSi electrodes are compared. Using Co2FeSi single layers a tunnel magnetoresistance of 52% is reached, whereas the magnetization of the Co2FeSi is only 75% of the expected value. By using [Co2MnSi/Co2FeSi]x10 multilayer electrodes the magnetoresistance can be increased to 114% and the full bulk magnetization is reached. All junctions show an inverse tunnel magnetoresistance, when the electrons are tunneling from the Co–Fe into the Heusler compound electrode. This results from a special band structure feature of full Heusler compounds, which is robust even for atomic disorder in the films.
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75.47.Np Metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.21.Ac Multilayers

Ultralow resistance-area product of 0.4 Ω(μm)2 and high magnetoresistance above 50% in CoFeB/MgO/CoFeB magnetic tunnel junctions

Yoshinori Nagamine, Hiroki Maehara, Koji Tsunekawa, David D. Djayaprawira, Naoki Watanabe, Shinji Yuasa, and Koji Ando

Appl. Phys. Lett. 89, 162507 (2006); http://dx.doi.org/10.1063/1.2352046 (3 pages) | Cited 37 times

Online Publication Date: 17 October 2006

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An ultralow resistance-area (RA) product of 0.4 Ω(μm)2 was achieved in CoFeB/MgO/CoFeB magnetic tunnel junctions with a high magnetoresistance ratio of 57% at room temperature. Various growth conditions for polycrystalline MgO(001) tunneling barrier were optimized to improve the crystalline orientation of the MgO(001) layer, which resulted in a significant enhancement of magnetoresistance in an ultralow RA region below 1 Ω(μm)2. Removal of residual H2O molecules from a growth chamber was especially effective in improving the crystalline orientation. The present achievements will enable the development of highly sensitive read heads for ultrahigh-density hard disk drives.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Ss Magnetic recording materials
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Ultrasonic study on magnetic-field-induced stripe order in La1.88Sr0.12−xBaxCuO4

J. F. Qu, Y. Q. Zhang, X. L. Lu, X. Q. Xiang, Y. L. Liao, G. Li, and X. G. Li

Appl. Phys. Lett. 89, 162508 (2006); http://dx.doi.org/10.1063/1.2364120 (3 pages) | Cited 3 times

Online Publication Date: 18 October 2006

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The ultrasonic sound velocities and attenuations of La1.88Sr0.12−xBaxCuO4 (0 ⩽ x ⩽ 0.12) under magnetic fields of up to 14 T show two important features of charge stripe order in the system. The first is that the ultrasonic characteristics indicate the existence of local stripe order associated with low temperature tetragonal structure domains for samples with x ⩽ 0.04. The second is that the local stripe order can be enhanced by magnetic fields. The results indicate a strong interaction between charge stripes and crystal lattice in the system.
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74.72.-h Cuprate superconductors
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation

Analytical electron microscopy study of growth mechanism for smoothing of metallic multilayer thin films

O. Ozatay, K. A. Mkhoyan, M. G. Thomas, G. D. Fuchs, J. Silcox, and R. A. Buhrman

Appl. Phys. Lett. 89, 162509 (2006); http://dx.doi.org/10.1063/1.2358958 (3 pages)

Online Publication Date: 18 October 2006

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We have used scanning transmission electron microscopy and electron energy-loss spectroscopy techniques to study the nature of interfacial interactions in a Ta/CuOx stack that give rise to a smooth surface morphology, which can be utilized for seeding thin magnetic multilayer devices. Our measurements reveal that the interfacial smoothing is mainly due to the preferential reaction of Ta with O at the Ta/CuOx interface assisted by grain boundary diffusion of oxygen which thereby acts to smooth out the surface roughness created by the large crystalline grains of Cu.
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68.37.Lp Transmission electron microscopy (TEM)
68.65.Ac Multilayers
79.20.Uv Electron energy loss spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
61.72.Mm Grain and twin boundaries

Stacking faults in YBa2Cu3O7−x: Measurement using x-ray diffraction and effects on critical current

E. D. Specht, A. Goyal, J. Li, P. M. Martin, X. Li, and M. W. Rupich

Appl. Phys. Lett. 89, 162510 (2006); http://dx.doi.org/10.1063/1.2364185 (3 pages) | Cited 20 times

Online Publication Date: 18 October 2006

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The density n of stacking faults (SFs) in epitaxial YBa2Cu3O7−x (Y123) films, consisting of extra CuO planes, is measured by fitting x-ray diffraction patterns using a random stacking model. The SF density is n = 0.068 nm−1 in films grown by metal-organic deposition on textured templates and optimized for high Ic. The presence of SF is correlated with pinning of magnetic field (H) applied in the Y123 ab plane. SF can be nearly eliminated by a high temperature anneal, or by adding excess Dy, resulting in Ic which is nearly independent of the orientation of H.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
61.72.Nn Stacking faults and other planar or extended defects

Anisotropic Sm–Fe–N magnets produced by compression shearing method

Tetsuji Saito, Hisanobu Sato, Hiroyuku Takeishi, and Noboru Nakayama

Appl. Phys. Lett. 89, 162511 (2006); http://dx.doi.org/10.1063/1.2362589 (2 pages) | Cited 4 times

Online Publication Date: 19 October 2006

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Sm–Fe–N bulk magnet was produced by the compression shearing method. X-ray diffraction studies revealed that the magnet retained the original Sm2Fe17N3 phase structure without any appreciable decomposition of the Sm2Fe17N3 phase and that this phase had a pronounced crystallographic alignment. Magnetic measurements confirmed that the Sm–Fe–N magnet was magnetically anisotropic. The bulk anisotropic Sm–Fe–N magnet exhibited a high remanence value of 9.43 kG with a high coercivity of 11.0 kOe.
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75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
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