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9 Dec 2002

Volume 81, Issue 24, pp. 4499-4663

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Tunable ferromagnetic resonance peak in tunneling magnetoresistive sensor structures

Alexey V. Nazarov, Hae Seok Cho, Janusz Nowak, Scott Stokes, and Ned Tabat

Appl. Phys. Lett. 81, 4559 (2002); http://dx.doi.org/10.1063/1.1521578 (3 pages) | Cited 17 times

Online Publication Date: 3 December 2002

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Noise properties of submicron scale tunneling magnetoresistive (TMR) sensors were investigated at frequencies up to 3 GHz. Noise spectral density was measured as a function of frequency, applied field, and bias current. Noise spectral density versus frequency dependence exhibits a pronounced peak, tunable over a wide frequency range. This peak appears to originate from current-driven precession of magnetization. The peak center frequency can be as low as 200 MHz and has a strong dependence on applied field and bias current. The damping constant α of the main precession mode in the TMR sensor free layer was found to be in the range of 0.05–0.18. It is shown that the magnetic state of a magnetoresistive sensor depends on the bias current and may be characterized by noise properties. The magnetoresistive element can operate as a source of high-frequency radiation with 1 nW emitting power from a 0.1 μm2 junction and signal to noise ratio of 10 dB. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.Mk Spin transport through interfaces
07.55.-w Magnetic instruments and components

Crossover of magnetotransport process toward spin-polarized tunneling in manganite thin films

T. Taniyama, M. Yamasaki, and Y. Yamazaki

Appl. Phys. Lett. 81, 4562 (2002); http://dx.doi.org/10.1063/1.1528282 (3 pages) | Cited 4 times

Online Publication Date: 3 December 2002

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We report on the magnetoresistive features of well-characterized polycrystalline manganite thin films as a function of film thickness. A crossover of the magnetization process from domain wall displacement to magnetic rotation of each grain is observed around a thickness of 25 nm, accompanied with the maximum of the coercivity. The thickness dependence of the electrical resistivity clearly distinguishes the transport mechanism at 25 nm, below which the magnetoresistance can be well scaled by ∼ (M/MS)2, using the magnetization M and the saturation magnetization MS. Spin-polarized tunneling transport between adjacent grains provides a comprehensive picture for the magnetotransport data. © 2002 American Institute of Physics.
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72.25.-b Spin polarized transport
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Thickness dependence of exchange bias and structure in MnPt and MnNi spin valves

Michael F. Toney, Mahesh G. Samant, Tsann Lin, and Daniele Mauri

Appl. Phys. Lett. 81, 4565 (2002); http://dx.doi.org/10.1063/1.1528279 (3 pages) | Cited 18 times

Online Publication Date: 3 December 2002

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We describe x-ray diffraction and magnetic measurements of annealed MnPt and NiMn spin valves as a function of MnPt (NiMn) film thickness. Thin films (≲5–10 nm) are not chemically ordered and hence not antiferromagnetic, which explains the lack of exchange coupling in these films. With increasing thickness, the L10 chemical order develops (through coexistence between fcc and L10 phases) and there is a strong correlation between chemical order and exchange coupling. The lack of chemical order in the thin films is likely due to a lack of nucleation sites for the L10 phase. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Superconductivity depression in ultrathin YBa2Cu3O7−δ layers in La0.7Ca0.3MnO3/YBa2Cu3O7−δ superlattices

Z. Sefrioui, M. Varela, V. Peña, D. Arias, C. León, J. Santamaría, J. E. Villegas, J. L. Martínez, W. Saldarriaga, and P. Prieto

Appl. Phys. Lett. 81, 4568 (2002); http://dx.doi.org/10.1063/1.1526463 (3 pages) | Cited 46 times

Online Publication Date: 3 December 2002

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We report on the depression of the superconducting critical temperature of ultrathin YBa2Cu3O7 (YBCO) layers, when their thickness is reduced in the presence of La0.7Ca0.3MnO3 (LCMO) magnetic layers in [LCMO (15 unit cells)/YBCO (N unit cells)] superlattices. The thickness of the manganite layer is kept at 15 unit cells and the YBCO thickness is varied between N = 12 and N = 1 unit cells. The structural analysis, using x-ray diffraction and electron microscopy, shows sharp interfaces with little structural disorder. While a critical temperature, TC = 85 K, is found for 12 YBCO unit cells, superconductivity is completely suppressed for YBCO layer thickness below 3 unit cells. The possible interaction between superconductivity and magnetism is investigated. © 2002 American Institute of Physics.
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74.78.Fk Multilayers, superlattices, heterostructures
74.72.-h Cuprate superconductors
74.62.Yb Other effects
68.65.Cd Superlattices
75.50.Dd Nonmetallic ferromagnetic materials

Role of SrRuO3 buffer layers on the superconducting properties of YBa2Cu3O7 films grown on polycrystalline metal alloy using a biaxially oriented MgO template

Q. X. Jia, S. R. Foltyn, P. N. Arendt, J. R. Groves, T. G. Holesinger, M. E. Hawley, and P. Lu

Appl. Phys. Lett. 81, 4571 (2002); http://dx.doi.org/10.1063/1.1527699 (3 pages) | Cited 27 times

Online Publication Date: 3 December 2002

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A SrRuO3 (SRO) buffer layer has been developed for growth of superconducting YBa2Cu3O7 (YBCO) thick films on polycrystalline metal substrates where a biaxially oriented MgO layer—produced by ion-beam-assisted deposition (IBAD)—was used as a template. By using such an architecture, we have routinely deposited YBCO films with an in-plane mosaic spread in the range of 3°–6° in full width at half maximum. A critical current density of 3.0×106 A/cm2 in self-field at 75 K for a film thickness of over 1.3 μm has been achieved. We believe that the SRO buffer layer plays a significant role in the much improved performance of YBCO conductors built on IBAD MgO. The features of SRO, such as good lattice match with both MgO and YBCO, excellent thermal stability in an oxidizing environment, and planarization of growing surface, make it the ideal choice as the buffer layer for high-performance superconductor coatings. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects
74.72.-h Cuprate superconductors

Magnetic properties of self-assembled interacting nanoparticles

D. Kechrakos and K. N. Trohidou

Appl. Phys. Lett. 81, 4574 (2002); http://dx.doi.org/10.1063/1.1528290 (3 pages) | Cited 18 times

Online Publication Date: 3 December 2002

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The temperature-dependent magnetization and the hysteresis properties (remanence and coercivity) of magnetic nanoparticle arrays are studied by Monte Carlo simulations. An oscillatory variation of the remanence with layer coverage and accompanying peaks in the coercive field are predicted at low temperatures, due to dipolar interparticle interactions. The blocking temperature of the arrays decreases with the inverse cube of the interparticle spacing (Tb ∼ d−3) and it remains almost unchanged with film thickness above one monolayer. Our results are compared with recent experiments on self-assembled Co nanoparticle arrays. © 2002 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Mg Numerical simulation studies
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys

Significant enhancement of irreversibility field in clean-limit bulk MgB2

V. Braccini, L. D. Cooley, S. Patnaik, D. C. Larbalestier, P. Manfrinetti, A. Palenzona, and A. S. Siri

Appl. Phys. Lett. 81, 4577 (2002); http://dx.doi.org/10.1063/1.1528289 (3 pages) | Cited 37 times

Online Publication Date: 3 December 2002

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Low resistivity MgB2 bulk samples annealed in Mg vapor show an increase in irreversibility field μ0H∗(T) by a factor of ∼2 in both transport and magnetic measurements. The best sample displayed a magnetic irreversibility field μ0HM∗>14 T at 4.2 K and ∼6 T at 20 K. These changes were accompanied by an increase of the 40 K resistivity from 1 to 18 μΩ cm and a lowering of the resistivity ratio from 15 to 3, while the critical temperature Tc decreased by only 1–2 K. These results show that systematic processing changes can make MgB2 attractive for magnet applications. © 2002 American Institute of Physics.
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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
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