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8 Sep 2008

Volume 93, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 93, 101905 (2008); http://dx.doi.org/10.1063/1.2977760 (3 pages)

Mei Wang, Yinwei Li, Tian Cui, Yanming Ma, and Guangtian Zou
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A study of multirow-per-track bit patterned media by spinstand testing and magnetic force microscopy

Y. J. Chen, T. L. Huang, S. H. Leong, S. B. Hu, K. W. Ng, Z. M. Yuan, B. Y. Zong, B. Liu, and V. Ng

Appl. Phys. Lett. 93, 102501 (2008); http://dx.doi.org/10.1063/1.2978326 (3 pages) | Cited 9 times

Online Publication Date: 8 September 2008

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We propose and demonstrate a concept of multirow-per-track bit patterned media (BPM) recording to overcome the problems encountered with the conventional one-row-per-track design. Focused ion beam was used on continuous granular perpendicular magnetic media to fabricate the prototype structures consisting of birow tracks with sub-100-nm single domain magnetic islands with the two rows of islands to be interleaved along the track direction, as well as an additional nonmagnetic spacer band between adjacent birow tracks for further bit aspect ratio (BAR) ≥ 2 adjustment. Readback from such birow tracks with a two-row-wide read head was performed by dynamic spinstand testing. The proposed concept BPM provides many advantages including higher linear recording density (under the same lithographic limit), therefore enabling a higher data rate and a greater BAR ≥ 2 for better integration with head design and servocontrol, as well as allowing the use of wider thus larger recording heads to improve writing efficiency for high density recording.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ss Magnetic recording materials

Study of spin fluctuations in Ni3±xAl1∓x using point contact Andreev reflection spectroscopy

Sourin Mukhopadhyay, Sudesh Kumar Dhar, and Pratap Raychaudhuri

Appl. Phys. Lett. 93, 102502 (2008); http://dx.doi.org/10.1063/1.2979687 (3 pages) | Cited 1 time

Online Publication Date: 8 September 2008

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We report point contact Andreev reflection (PCAR) spectroscopy studies on Ni3±xAl1∓x with composition range spanning the ferromagnetic to paramagnetic phase boundary. PCAR studies performed using Nb tip as counterelectrode reveal that the superconducting quasiparticle lifetime (τ) and superconducting energy gap (Δ) decrease with increasing spin fluctuation in the normal metal electrode. Our study reveals that PCAR could be a useful probe to study spin fluctuations in systems that are on the verge of magnetic instability.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.50.+r Tunneling phenomena; Josephson effects
74.25.Jb Electronic structure (photoemission, etc.)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.20.Mn Nonconventional mechanisms

Converse magnetoelectric effects on heterotype electrostrain-piezopermeability composites

X. Fang, N. Zhang, and Z. L. Wang

Appl. Phys. Lett. 93, 102503 (2008); http://dx.doi.org/10.1063/1.2979699 (3 pages) | Cited 8 times

Online Publication Date: 8 September 2008

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By using the product effect of electrostrain and piezopermeability, a heterotype composite consisting of a bar of Pb(Zr,Ti)O3 and a ring of MnZn ferrite with higher permeability has been developed, and its converse magnetoelectric effect has been investigated. Under a constant electric field of 5 kV/cm, about 20% electric-field-induced changes in permeability and impedance have been observed with the composite device over a wide frequency band. The electric-field dependence of the permeability and impedance shows a ferroelectric relaxation behavior. This composite is a candidate material for electrically controlled magnetic devices.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.84.Lf Composite materials
77.65.-j Piezoelectricity and electromechanical effects
77.22.Gm Dielectric loss and relaxation
77.80.-e Ferroelectricity and antiferroelectricity

A microwave nonlinear phase shifter

Alexey B. Ustinov and Boris A. Kalinikos

Appl. Phys. Lett. 93, 102504 (2008); http://dx.doi.org/10.1063/1.2980022 (3 pages) | Cited 4 times

Online Publication Date: 8 September 2008

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A microwave nonlinear phase shifter is described. It is a device producing a power-dependent phase shift of microwave signals. The device is fabricated with a ferrite film which serves as a waveguide for magnetostatic spin waves. A nonlinear phase shift of the carrier spin waves appearing under increasing their power is the key phenomenon in the device operation. A theoretical model for the nonlinear phase shifter is presented. The model provides a good description for the experimentally obtained performance characteristics of the device.
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84.40.-x Radiowave and microwave (including millimeter wave) technology

Irreversible magnetic exchange-spring processes in antiferromagnetic exchange-coupled bilayer systems

Guang-hua Guo, Guang-fu Zhang, San-yuan Song, D. W. Wang, G. J. Bowden, and P. A. J. de Groot

Appl. Phys. Lett. 93, 102505 (2008); http://dx.doi.org/10.1063/1.2972028 (3 pages) | Cited 1 time

Online Publication Date: 9 September 2008

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The demagnetization processes of antiferromagnetic exchange-coupled hard-soft bilayer structures have been studied using a one-dimensional atomic chain model, taking into account the anisotropies of both hard and soft layers. It is found that for very thin soft layers, magnetization/demagnetization involves typical reversible exchange-spring behavior. However as the thickness t of the soft layer is increased, there is a crossover point tc, after which the exchange spring becomes irreversible. The value of the critical thickness tc is determined inter alia by the magnetic anisotropy of the soft layer. However, an important feature of the irreversible exchange spring is the formation of a large angle domain wall, realized immediately at the bending field transition.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.50.Ee Antiferromagnetics

Magnetization switching behavior with microwave assistance

S. Okamoto, N. Kikuchi, and O. Kitakami

Appl. Phys. Lett. 93, 102506 (2008); http://dx.doi.org/10.1063/1.2977474 (3 pages) | Cited 17 times

Online Publication Date: 9 September 2008

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Microwave assisted switching of magnetization has become one of the key techniques for future advanced recording. We have studied the magnetization switching behaviors excited by circularly and linearly polarized microwaves based on the Landau–Lifshitz–Gilbert equation. The precessional motion of magnetization is excited by the microwave, resulting in significant reduction of the irreversible reversal field. The reversal takes place through very complicated precessional motion, which proceeds via nearly steady precession at an early stage, subsequent unstable motion, and finally abrupt irreversible switching. We discuss the detailed effect of microwave polarization on magnetization reversals.
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75.60.Jk Magnetization reversal mechanisms
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Combinatorial investigation of magnetostriction in Fe–Ga and Fe–Ga–Al

Jason R. Hattrick-Simpers, Dwight Hunter, Corneliu M. Craciunescu, Kyu Sung Jang, Makoto Murakami, James Cullen, Manfred Wuttig, Ichiro Takeuchi, Samuel E. Lofland, Leonid Benderksy, Noble Woo, Robert Bruce Van Dover, Toshiya Takahashi, and Yasubumi Furuya

Appl. Phys. Lett. 93, 102507 (2008); http://dx.doi.org/10.1063/1.2980034 (3 pages) | Cited 7 times

Online Publication Date: 9 September 2008

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A high-throughput high-sensitivity optical technique for measuring magnetostriction of thin-film composition-spread samples has been developed. It determines the magnetostriction by measuring the induced deflection of micromachined cantilever unimorph samples. Magnetostriction measurements have been performed on as-deposited Fe–Ga and Fe–Ga–Al thin-film composition spreads. The thin-film Fe–Ga spreads display a similar compositional variation of magnetostriction as bulk. A previously undiscovered peak in magnetostriction at low Ga content was also observed and attributed to a maximum in the magnetocrystalline anisotropy. Magnetostrictive mapping of the Fe–Ga–Al ternary system reveals the possibility of substituting up to 8 at. % Al in Fe70Ga30 without significant degradation of magnetostriction.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

Relationship between symmetry and scaling of spin torque thermal switching barrier

Xiaobin Wang, Wenzhong Zhu, Haiwen Xi, and Dimitar Dimitrov

Appl. Phys. Lett. 93, 102508 (2008); http://dx.doi.org/10.1063/1.2976781 (3 pages)

Online Publication Date: 10 September 2008

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This letter shows that the scaling relationship between the thermal reversal barrier and the (spin polarized) current density in the limit of low current density strongly depends on magnetization dynamics symmetry. This is quite different from magnetic field induced thermal switching. Our analysis demonstrates that the widely used scaling relationship between switching time and current density needs to be modified to include magnetization dynamics symmetry effects. A formula for a thermal reversal barrier symmetry correction factor is given in the limit of low current density. The implications for the estimation of magnetic element thermal stability are discussed.
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72.25.-b Spin polarized transport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High-output current-perpendicular to the plane giant magnetoresistance sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents

M. J. Carey, N. Smith, S. Maat, and J. R. Childress

Appl. Phys. Lett. 93, 102509 (2008); http://dx.doi.org/10.1063/1.2978328 (3 pages) | Cited 6 times

Online Publication Date: 10 September 2008

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It is shown that the maximum stable output of a current-perpendicular to the plane giant magnetoresistance sensor is increased significantly by using a synthetic-ferrimagnet free layer, provided the electron current flows from free layer to reference layer. This free layer allows a larger magnetoresistance ratio for a given free layer magnetic moment, and in addition results in a greater than threefold increase in the critical current, above which spin-torque instability of the free layer occurs. In read heads with net free layer moments equivalent to only 4.5 nm of Ni80Fe20, this effect is shown to result in sustainable sense current densities above 2×108 A/cm2.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.75.Ss Magnetic field sensors using spin polarized transport
75.50.Gg Ferrimagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.47.De Giant magnetoresistance

Hydrothermal epitaxy of ZnO:Co diluted magnetic semiconducting single crystalline films

Y. B. Zhang, S. Li, G. K. L. Goh, and S. Tripathy

Appl. Phys. Lett. 93, 102510 (2008); http://dx.doi.org/10.1063/1.2981518 (3 pages) | Cited 7 times

Online Publication Date: 10 September 2008

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ZnO:Co films with room-temperature ferromagnetism have been hydrothermally grown in water at 90 °C using a ZnO seed layer on MgAl2O4 (111) substrates. High-resolution x-ray diffraction shows an epitaxial ZnO:Co single crystalline film with an out-of-plane orientation of ZnO:Co〈001〉∥MgAl2O4〈111〉 and an in-plane orientation of ZnO:Co[110]∥MgAl2O4[−1−12] and ZnO:Co[−110]∥MgAl2O4[−110]. A saturation magnetization of 0.83 emu/cm3 and a coercivity of 40 Oe were obtained for the epitaxial Zn0.98Co0.02O film at room temperature. Hydrogen unintentionally incorporated in the hydrothermal synthesis is suggested to contribute to the ferromagnetic properties in the diluted magnetic semiconductor by enhancing carrier concentration as a shallow donor.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
72.80.Ey III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Grain size reduction for perpendicular magnetic recording media using an Ar-ion etched Ru seedlayer

Hua Yuan and David E. Laughlin

Appl. Phys. Lett. 93, 102511 (2008); http://dx.doi.org/10.1063/1.2979685 (3 pages) | Cited 3 times

Online Publication Date: 11 September 2008

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We report an approach to reduce grain size for perpendicular media by using an Ar-ion etched Ru seedlayer. The surface etching affects the microstructure of the subsequent high pressure deposited Ru2+SiO2 interlayer and magnetic layer, whose grain size can be controlled. SiO2 in the interlayer plays a more important role in grain size reduction on the etched seedlayer than the as-grown seedlayer. Small Ru2 grains ∼ 3.9 nm and magnetic grains ∼ 5.3 nm with uniform distribution have been obtained. Thinner Ru grain boundaries with reduced size could be the cause of nonideal one-to-one grain growth and degraded magnetic properties.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.65.Cf Surface cleaning, etching, patterning
75.50.Ss Magnetic recording materials
81.30.Bx Phase diagrams of metals, alloys, and oxides

Reversibility of magnetostructural transition and associated magnetocaloric effect in Ni–Mn–In–Co

Jian Liu, Nils Scheerbaum, Julia Lyubina, and Oliver Gutfleisch

Appl. Phys. Lett. 93, 102512 (2008); http://dx.doi.org/10.1063/1.2981210 (3 pages) | Cited 22 times

Online Publication Date: 12 September 2008

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By analyzing isothermal magnetization curves under magnetic field cycling, the reversibility of the magnetostructural transition was investigated in Ni–Mn–In–Co in form of bulk sample and melt-spun ribbons. The hysteresis of thermally/magnetically induced martensitic transformation plays an important role in the reversibility of the magnetostructural transition. In ribbons with a large hysteresis of 18 K, residual field-induced austenite is present after removing the magnetic field, while, in the bulk sample, the magnetostructural transition is reversible at moderate temperatures due to a relatively smaller hysteresis of 8 K. Additionally, the magnetocaloric effect strongly depends on the sample history due to the occurrence of the irreversible magnetostructural transition, especially for the ribbons.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

An amplifier concept for spintronics

Y. Acremann, X. W. Yu, A. A. Tulapurkar, A. Scherz, V. Chembrolu, J. A. Katine, M. J. Carey, H. C. Siegmann, and J. Stöhr

Appl. Phys. Lett. 93, 102513 (2008); http://dx.doi.org/10.1063/1.2977964 (3 pages) | Cited 1 time

Online Publication Date: 12 September 2008

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Typical spin-dependent devices proposed for information processing lack one of the most important features provided by charge based logic: they do not provide gain. In this letter we show the basic concept of a spin amplifier and propose ways to amplify a spin current at room temperature.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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