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26 Apr 2010

Volume 96, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 96, 173501 (2010); http://dx.doi.org/10.1063/1.3409475 (3 pages)

Seoung-Ki Lee, Houk Jang, Musarrat Hasan, Jae Bon Koo, and Jong-Hyun Ahn
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Microstrip superconducting quantum interference device amplifier: Conditional stability

D. Kinion and John Clarke

Appl. Phys. Lett. 96, 172501 (2010); http://dx.doi.org/10.1063/1.3377898 (3 pages) | Cited 4 times

Online Publication Date: 26 April 2010

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The scattering parameters of an amplifier based on a dc superconducting quantum interference device are directly measured at 4.2 K as functions of the bias current and applied magnetic flux. These parameters are used to determine the stability of the amplifier with arbitrary source and output load impedances. It was found that the amplifier is conditionally stable, and that the stability is improved by decreasing the gain or adding negative feedback. With suitable bias selection, the amplifier is shown to be sufficiently stable to allow operation with a resonant source impedance.
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84.40.Az Waveguides, transmission lines, striplines
85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.30.Le Amplifiers

Anomalous magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films

Anna Zukova, Arunas Teiserskis, Y. K. Gun’ko, Ana M. Sánchez, and Sebastiaan van Dijken

Appl. Phys. Lett. 96, 172502 (2010); http://dx.doi.org/10.1063/1.3418622 (3 pages) | Cited 2 times

Online Publication Date: 26 April 2010

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We report on large external magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films on MgO(001). The application of a 1 T field during the growth process significantly increases the saturation magnetization of magnetite by 150%–220% at a deposition temperature of 550 and 600 °C, while the enhancement of the remanent magnetization is even larger. This anomalous magnetic field effect does not drastically alter the crystalline texture, surface morphology, and film thickness of magnetite, but is explained by a suppression of antiphase-boundary formation during film growth.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.jm Texture

Magnetoresistance and magnetocaloric effect at a structural phase transition from a paramagnetic martensitic state to a paramagnetic austenitic state in Ni50Mn36.5In13.5 Heusler alloys

Arjun K. Pathak, Igor Dubenko, Christopher Pueblo, Shane Stadler, and Naushad Ali

Appl. Phys. Lett. 96, 172503 (2010); http://dx.doi.org/10.1063/1.3422483 (3 pages) | Cited 11 times

Online Publication Date: 27 April 2010

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It is established, using magnetization measurements, that Ni50Mn36.5In13.5 is in a paramagnetic state (PS) above and below the martensitic transition temperature (TM). Magnetoresistance (MR) and magnetic entropy changes (ΔSM) in the vicinity of TM were studied. MR and ΔSM at TM were found to be ≈−8% and ≈ +24 J Kg−1 K−1, respectively, at ΔH = 5 T. Although MR and ΔSM values were lower than compared to those found in other Heusler systems, the significantly smaller hysteresis observed in Ni50Mn36.5In13.5 makes this compound, and other such compounds that undergo a martensitic transition in a PS, promising for the study and applications of magnetocaloric magnetic materials.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
64.70.kd Metals and alloys
81.30.Kf Martensitic transformations
75.20.En Metals and alloys
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Giant magnetocaloric effects by tailoring the phase transitions

N. T. Trung, L. Zhang, L. Caron, K. H. J. Buschow, and E. Brück

Appl. Phys. Lett. 96, 172504 (2010); http://dx.doi.org/10.1063/1.3399773 (3 pages) | Cited 18 times

Online Publication Date: 27 April 2010

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The MnCoGe alloy can crystallize in either the hexagonal Ni2In- or the orthorhombic TiNiSi-type of structure. In both phases MnCoGe behaves like a typical ferromagnet with a second-order magnetic phase transition. For MnCoGeBx with B on interstitial positions, we discover a giant magnetocaloric effect associated with a single first-order magnetostructural phase transition, which can be achieved by tuning the magnetic and structural transitions to coincide. The results obtained on the MnCoGe-type alloys may be extensible to other types of magnetic materials undergoing a first-order structural transformation and can open up some possibilities for searching magnetic refrigerants for room-temperature applications.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

High temperature magnetic properties of cobalt ferrite nanoparticles

A. Franco and F. C. e Silva

Appl. Phys. Lett. 96, 172505 (2010); http://dx.doi.org/10.1063/1.3422478 (3 pages) | Cited 26 times

Online Publication Date: 29 April 2010

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Cobalt ferrite materials have a wide variety of technological applications that requires temperatures higher than room temperature. Thus the magnetic properties such as saturation magnetization, Ms remanent magnetization, Mr, coercivitty, Hc, and Curie temperature, Tc, of nanoparticles of CoFe2O4 were studied in a broad range of temperature varying from room temperature to 870 K. It was observed that, for temperatures 100 K above room temperature, these magnetic properties are still the same as at room temperature. The results were discussed in terms of interparticle interactions induced by the thermal fluctuations, cation distribution, and other imperfections that exert fields on Co2+ ions could increase with temperature.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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