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14 Jan 2008

Volume 92, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 92, 022509 (2008); http://dx.doi.org/10.1063/1.2807274 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, and Youn-Seok Choi
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Lattice-strain control of magnetoresistivity and magnetoresistive anisotropy induced by ion-beam milling in La0.65Ca0.35MnO3 films near the metal-insulator transition

M. Egilmez, A. I. Mansour, M. M. Saber, K. H. Chow, and J. Jung

Appl. Phys. Lett. 92, 022501 (2008); http://dx.doi.org/10.1063/1.2827192 (3 pages) | Cited 7 times

Online Publication Date: 14 January 2008

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The lattice-disorder-induced changes in the magnetoresistivity and the magnetoresistive anisotropy of epitaxial ion-beam-milled La0.65Ca0.35MnO3 films were investigated. The results suggest that, for films less than 20 nm thick, an increase of the magnetoresistivity and a reduction in the magnetoresistive anisotropy of the ion-beam-milled films are governed mostly by the point-defect-induced deformation, in contrast to the as-grown films where an increase of both the magnetoresistivity and the magnetoresistive anisotropy is determined by the epitaxial strain.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.30.Gw Magnetic anisotropy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.30.+h Metal-insulator transitions and other electronic transitions

Dual-layer patterned media “ledge” design for ultrahigh density magnetic recording

Vitaliy Lomakin, Richard Choi, Boris Livshitz, Shaojing Li, Akihiro Inomata, and H. Neal Bertram

Appl. Phys. Lett. 92, 022502 (2008); http://dx.doi.org/10.1063/1.2831732 (3 pages) | Cited 19 times

Online Publication Date: 14 January 2008

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Patterned media elements comprising coupled magnetically hard and soft sections of different horizontal size, referred to as ledge elements, are characterized by several unique properties. These elements allow for remarkably reduced reversal fields, which are an order of magnitude below the Stoner-Wohlfarth limit. They also allow for precessional reversal to occur for practical field rise times (100–200 ps), which are two orders of magnitude larger than those in the case of homogeneous elements ( ∼ 2 ps). These attractive properties are obtained even for elements of small height (4–8 nm). Patterned media implementing such ledge elements can allow for recording densities above 10 Tbit/in2.
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75.50.Ss Magnetic recording materials
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Thermomagnetic history dependence of magnetocaloric effect in Ni50Mn34In16

M. K. Chattopadhyay, V. K. Sharma, and S. B. Roy

Appl. Phys. Lett. 92, 022503 (2008); http://dx.doi.org/10.1063/1.2831919 (3 pages) | Cited 18 times

Online Publication Date: 14 January 2008

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A large inverse magnetocaloric effect has been reported to be associated with the austenite to martensite phase transition in Ni50Mn34In16. It is shown here that the magnitude of the observed magnetocaloric effect as well as effective refrigerant capacity depend significantly on the thermo-magnetic history of the sample.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.15.Jf Thermoelectric and thermomagnetic effects
75.30.Sg Magnetocaloric effect, magnetic cooling

Growth and physical property of epitaxial Co70Fe30 thin film on Si substrate via TiN buffer

C.-X. Ji, Feng Lu, Y. Austin Chang, J. Joshua Yang, and M. S. Rzchowski

Appl. Phys. Lett. 92, 022504 (2008); http://dx.doi.org/10.1063/1.2834706 (3 pages) | Cited 3 times

Online Publication Date: 15 January 2008

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Epitaxial Co70Fe30 films with the bcc structure were grown on a Si(001) substrate with TiN as a buffer by sputtering technique. The x-ray diffraction results confirmed the epitaxial nature of the films and the crystallographic relationship was determined as Co70Fe30(002)〈110〉//TiN(002)〈100〉//Si(004)〈100〉. The surface morphology characterized by atomic force microscopy on our films revealed that smooth surfaces could be obtained at growth temperatures below 350 °C. The strain state of 60 nm epitaxial Co70Fe30 films was studied as a function of growth temperature. Magnetization hysteresis loops of the films grown at 300 °C were measured using superconducting quantum interface device magnetometer.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.35.bd Metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Realization of spin-wave logic gates

T. Schneider, A. A. Serga, B. Leven, B. Hillebrands, R. L. Stamps, and M. P. Kostylev

Appl. Phys. Lett. 92, 022505 (2008); http://dx.doi.org/10.1063/1.2834714 (3 pages) | Cited 53 times

Online Publication Date: 15 January 2008

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We demonstrate the functionality of spin-wave logic exclusive-not-OR and not-AND gates based on a Mach-Zehnder-type interferometer which has arms implemented as sections of ferrite film spin-wave waveguides. Logical input signals are applied to the gates by varying either the phase or the amplitude of the spin waves in the interferometer arms. This phase or amplitude variation is produced by Oersted fields of dc current pulses through conductors placed on the surface of the magnetic films.
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84.30.Sk Pulse and digital circuits
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Origins of the damping in perpendicular media: Three component ferromagnetic resonance linewidth in Co–Cr–Pt alloy films

Nan Mo, Julius Hohlfeld, Misbah ul Islam, C. Scott Brown, Erol Girt, Pavol Krivosik, Wei Tong, Adnan Rebei, and Carl E. Patton

Appl. Phys. Lett. 92, 022506 (2008); http://dx.doi.org/10.1063/1.2834835 (3 pages) | Cited 14 times

Online Publication Date: 15 January 2008

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The 9.41 GHz ferromagnetic resonance field and linewidth have been measured as a function of the angle (θH) between the external magnetic field and film normal for a series of 17.5 nm thick Co–Cr–Pt alloy films. The linewidths ranged from hundreds of Oersted to kiloersted, with different values at θH = 0 and θH = 90° and additional minima and maxima for θH-values from 16° to 64°. The profiles can be fitted with a combination of inhomogeneity line broadening, grain boundary two magnon scattering, and magnon-electron (m-e) scattering processes, with a notably small Gilbert damping α-value of 0.004 for the m-e term.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
68.55.-a Thin film structure and morphology
75.30.Ds Spin waves

Two-dimensional spin diffusion in multiterminal lateral spin valves

D. Saha, D. Basu, M. Holub, and P. Bhattacharya

Appl. Phys. Lett. 92, 022507 (2008); http://dx.doi.org/10.1063/1.2834853 (3 pages) | Cited 2 times

Online Publication Date: 15 January 2008

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The effects of two-dimensional spin diffusion on spin extraction in lateral semiconductor spin valves have been investigated experimentally and theoretically. A ferromagnetic collector terminal of variable size is placed between the ferromagnetic electron spin injector and detector of a conventional lateral spin valve for spin extraction. It is observed that transverse spin diffusion beneath the collector terminal plays an important role along with the conventional longitudinal spin diffusion in describing the overall transport of spin carriers. Two-dimensional spin diffusion reduces the perturbation of the channel electrochemical potentials and improves spin extraction.
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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
85.30.-z Semiconductor devices

Enhanced exchange bias effects in a nanopatterned system consisting of two perpendicularly coupled ferromagnets

A. Bollero, B. Dieny, J. Sort, K. S. Buchanan, S. Landis, and J. Nogués

Appl. Phys. Lett. 92, 022508 (2008); http://dx.doi.org/10.1063/1.2833124 (3 pages) | Cited 3 times

Online Publication Date: 16 January 2008

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The effect of patterning on the shift of the hysteresis loop HE and coercivity HC in a system composed of two perpendicularly exchange-coupled ferromagnets (NiFe sputtered onto a [Pt/Co] multilayer) is investigated in long stripes and square dots. Setting the exchange bias coupling along the stripes results in a threefold increase of HE compared to the continuous films. HC increases dramatically when the coupling is set perpendicular to the stripes and also in the dots. Magnetic force microscopy studies and micromagnetic simulations suggest that differences in the number and orientation of the magnetic domains can account for the observed effects.
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75.75.-c Magnetic properties of nanostructures
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
75.30.Gw Magnetic anisotropy

Reliable low-power control of ultrafast vortex-core switching with the selectivity in an array of vortex states by in-plane circular-rotational magnetic fields and spin-polarized currents

Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, and Youn-Seok Choi

Appl. Phys. Lett. 92, 022509 (2008); http://dx.doi.org/10.1063/1.2807274 (3 pages) | Cited 46 times

Online Publication Date: 16 January 2008

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The authors investigated the technological utility of counterclockwise (CCW) and clockwise (CW) circular-rotating fields (HCCW and HCW) and spin-polarized currents with an angular frequency ωH close to the vortex eigenfrequency ωD, for the reliable, low-power, and selective switching of the bistate magnetization (M) orientations of a vortex core (VC) in an array of soft magnetic nanoelements. CCW and CW circular gyrotropic motions in response to HCCW and HCW, respectively, show remarkably contrasting resonant behaviors, (i.e., extremely large-amplitude resonance versus small-amplitude nonresonance), depending on the M orientation of a given VC. Owing to this asymmetric resonance characteristics, the HCCW (HCW) with ωH ∼ ωD can be used to effectively switch only the up (down) core to its downward (upward) M orientation, selectively, by sufficiently low field ( ∼ 10 Oe) and current density ( ∼ 107 A/cm2). This work provides a reliable, low power, effective means of information storage, information recording, and information readout in vortex-based random access memory, simply called VRAM.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
84.30.Sk Pulse and digital circuits

Controlling domain wall pinning in planar nanowires by selecting domain wall type and its application in a memory concept

D. Atkinson, D. S. Eastwood, and L. K. Bogart

Appl. Phys. Lett. 92, 022510 (2008); http://dx.doi.org/10.1063/1.2832771 (3 pages) | Cited 30 times

Online Publication Date: 16 January 2008

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Here, we report on the control of domain wall pinning at notch features patterned in Permalloy planar nanowires by selecting the micromagnetic configuration of the domain wall using a transverse magnetic field. The domain wall behavior was investigated both experimentally using focused magneto-optic Kerr effect measurements of lithographically patterned nanowires and with micromagnetic simulations. The pinning behavior observed is utilized in a concept for multibit memory cells applicable as the free layer in magnetic random access memory where the domain structure is defined by the location of domain walls that either pin or passby pinning structures depending upon the domain wall configuration selected.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
78.20.Ls Magneto-optical effects

Two-phonon coupling to the antiferromagnetic phase transition in multiferroic BiFeO3

Mariola O. Ramirez, M. Krishnamurthi, S. Denev, A. Kumar, Seung-Yeul Yang, Ying-Hao Chu, Eduardo Saiz, Jan Seidel, A. P Pyatakov, A. Bush, D. Viehland, J. Orenstein, R. Ramesh, and Venkatraman Gopalan

Appl. Phys. Lett. 92, 022511 (2008); http://dx.doi.org/10.1063/1.2829681 (3 pages) | Cited 22 times

Online Publication Date: 16 January 2008

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A prominent band centered at ∼ 1000–1300 cm−1 and associated with resonant enhancement of two-phonon Raman scattering is reported in multiferroic BiFeO3 thin films and single crystals. A strong anomaly in this band occurs at the antiferromagnetic Neel temperature, TN ∼ 375 °C. This band is composed of three peaks, assigned to 2A4, 2E8, and 2E9 Raman modes. While all three peaks were found to be sensitive to the antiferromagnetic phase transition, the 2E8 mode, in particular, nearly disappears at TN on heating, indicating a strong spin-two-phonon coupling in BiFeO3.
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63.20.kg Phonon-phonon interactions
78.30.Hv Other nonmetallic inorganics
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films

On-wafer microwave signal-to-noise enhancer using NiFe films

Y. V. Khivintsev, V. V. Zagorodnii, A. J. Hutchison, R. E. Camley, and Z. J. Celinski

Appl. Phys. Lett. 92, 022512 (2008); http://dx.doi.org/10.1063/1.2827576 (3 pages) | Cited 5 times

Online Publication Date: 17 January 2008

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This paper presents experimental results on a tunable microstrip signal-to-noise enhancer based on NiFe films. Structures involving the first- and second-order Suhl instabilities are compared. The enhancement factor is 10 dB for a structure involving only the second order instability and an enhancement factor of 30 dB is found for a structure where the first order instability is allowed.
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84.40.-x Radiowave and microwave (including millimeter wave) technology

High temperature ferromagnetism and perpendicular magnetic anisotropy in Fe-doped In2O3 films

P. F. Xing, Y. X. Chen, Shi-Shen Yan, G. L. Liu, L. M. Mei, K. Wang, X. D. Han, and Z. Zhang

Appl. Phys. Lett. 92, 022513 (2008); http://dx.doi.org/10.1063/1.2834369 (3 pages) | Cited 24 times

Online Publication Date: 18 January 2008

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High temperature ferromagnetism and perpendicular magnetic anisotropy were observed in Fe-doped In2O3 magnetic semiconductor films deposited on R-cut sapphire by pulse laser deposition. The films show a Curie temperature as high as 927 K. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.77 and a coercivity of 680 Oe is demonstrated. Extensive microstructure, composition, and magnetic studies indicate that Fe element incorporates into the indium oxide lattice by substituting the position of indium atoms, which suggests the observed ferromagnetism is intrinsic rather than from Fe clusters or any other magnetic impurity phases.
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75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Electrical control of magnon propagation in multiferroic BiFeO3 films

Rogerio de Sousa and Joel E. Moore

Appl. Phys. Lett. 92, 022514 (2008); http://dx.doi.org/10.1063/1.2835704 (3 pages) | Cited 14 times

Online Publication Date: 18 January 2008

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The spin wave spectra of multiferroic BiFeO3 films is calculated using a phenomenological Landau theory that includes magnetostatic effects. The lowest frequency magnon dispersion is shown to be quite sensitive to the angle between spin wave propagation vector and the Néel moment. Since electrical switching of the Néel moment has recently been demonstrated in this material, the sensitivity of the magnon dispersion permits direct electrical switching of spin wave propagation. This effect can be used to construct spin wave logical gates without current pulses, potentially allowing reduced power dissipation per logical operation.
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75.30.Ds Spin waves
75.80.+q Magnetomechanical effects, magnetostriction
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena
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