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7 Mar 2005

Volume 86, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 86, 103102 (2005); http://dx.doi.org/10.1063/1.1875734 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, and Motoichi Ohtsu
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Transport and magnetic Jc of MgB2 strands and small helical coils

M. D. Sumption, M. Bhatia, M. Rindfleisch, M. Tomsic, and E. W. Collings

Appl. Phys. Lett. 86, 102501 (2005); http://dx.doi.org/10.1063/1.1875753 (3 pages) | Cited 11 times

Online Publication Date: 1 March 2005

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The critical current densities of MgB2 monofilamentary strands with and without SiC additions were measured at 4.2 K. Additionally, magnetic Jc at B = 1 T was measured from 4.2 to 40 K. Various heat treatment times and temperatures were investigated for both short samples and small helical coils. SiC additions were seen to improve high field transport Jc at 4.2 K, but improvements were not evident at 1 T at any temperature. Transport results were relatively insensitive to heat treatment times and temperatures for both short samples and coils in the 700–900 °C range.
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84.71.Ba Superconducting magnets; magnetic levitation devices
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.F- Transport properties
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.40.Gh Other heat and thermomechanical treatments

Soft x-ray resonant Kerr rotation measurement and simulation of element-resolved and interface-sensitive magnetization reversals in a NiFe/FeMn/Co trilayer structure

Sang-Koog Kim, Ki-Suk Lee, J. B. Kortright, and Sung-Chul Shin

Appl. Phys. Lett. 86, 102502 (2005); http://dx.doi.org/10.1063/1.1873047 (3 pages) | Cited 10 times

Online Publication Date: 2 March 2005

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We report experimental observations of element- and buried interface-resolved magnetization reversals in an oppositely exchange-biased NiFe/FeMn/Co trilayer structure by soft x-ray resonant Kerr rotation measurements. Not only Co-, Ni-, Fe-specific exchange-biased loops but also interfacial uncompensated (UC) Fe reversal loops coupled to the individual Co and NiFe layers are separately observed. From the experimental results interpreted with the help of the model simulations of soft x-ray resonant Kerr rotation, the effective thicknesses of interfacial UC regions at the buried interfaces of both FeMn/Co and NiFe/FeMn are found to be tUC = 13±2 Å and 6±4 Å, respectively. The depth sensitivity as well as element specificity of the x-ray resonant Kerr effect offer an elegant way into the investigations of element- and depth-resolved magnetization reversals of ferromagnetic ultrathin regions at buried interfaces in multicomponent multilayer films.
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75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.30.Et Exchange and superexchange interactions
78.20.Ls Magneto-optical effects
68.55.-a Thin film structure and morphology

Fabrication and uniaxial magnetic anisotropy of Co nanowires on a Pd(110) surface

L. Yan, M. Przybylski, Yafeng Lu, W. H. Wang, J. Barthel, and J. Kirschner

Appl. Phys. Lett. 86, 102503 (2005); http://dx.doi.org/10.1063/1.1870127 (3 pages) | Cited 13 times

Online Publication Date: 3 March 2005

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We have fabricated Co atomic chains and nanowires on a Pd(110) surface oriented along the [1-10] direction. This is possible due to high diffusion anisotropy of the Co adatom on the Pd(110) surface. The Co nanowires on Pd(110) exhibit a strong uniaxial in-plane magnetic anisotropy, in which the easy axis is along [1-10], i.e., nanowire direction.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ss Magnetic recording materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
81.05.Bx Metals, semimetals, and alloys
81.16.-c Methods of micro- and nanofabrication and processing
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.75.-c Magnetic properties of nanostructures
68.35.Fx Diffusion; interface formation
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of doping on the magnetic properties of GaMnN: Fermi level engineering

M. J. Reed, F. E. Arkun, E. A. Berkman, N. A. Elmasry, J. Zavada, M. O. Luen, M. L. Reed, and S. M. Bedair

Appl. Phys. Lett. 86, 102504 (2005); http://dx.doi.org/10.1063/1.1881786 (3 pages) | Cited 39 times

Online Publication Date: 3 March 2005

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GaMnN dilute magnetic semiconductor samples, prepared by metalorganic chemical vapor deposition, are shown to exhibit ferromagnetism or even paramagnetism depending upon the type and concentration of extrinsic impurity present in the film. In addition, GaMnN deposited using growth parameters normally yielding a nonferromagnetic film becomes strongly ferromagnetic with the addition of magnesium, an acceptor dopant. Based upon these observations, it seems that ferromagnetism in this material system depends on the relative position of the Mn energy band and the Fermi level within the GaMnN band gap. Only when the Fermi level closely coincides with the Mn-energy level is ferromagnetism achieved. By actively engineering the Fermi energy to be within or near the Mn energy band, room temperature ferromagnetism is realized.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
71.55.Eq III-V semiconductors
75.20.Ck Nonmetals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.20.At Surface states, band structure, electron density of states
61.72.S- Impurities in crystals

Emissivity — a remote sensor of giant magnetoresistance

S. M. Stirk, S. M. Thompson, and J. A. D. Matthew

Appl. Phys. Lett. 86, 102505 (2005); http://dx.doi.org/10.1063/1.1880437 (3 pages) | Cited 15 times

Online Publication Date: 3 March 2005

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The link between emissivity in the mid-to-far-infrared regime and electrical conductivity is used to probe magnetoresistance. A direct relationship between the change in radiated flux and giant magnetoresistance is confirmed by experiment. The potential for spatially resolved measurements is also considered.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Bias-voltage dependence of magnetoresistance in magnetic tunnel junctions grown on Al2O3 (0001) substrates

Sung-Jin Ahn, Takeharu Kato, Hitoshi Kubota, Yasuo Ando, and Terunobu Miyazaki

Appl. Phys. Lett. 86, 102506 (2005); http://dx.doi.org/10.1063/1.1870104 (3 pages) | Cited 6 times

Online Publication Date: 4 March 2005

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Magnetic tunnel junctions with the structure of Al2O3 (0001)/Pt (111) 20 nm/Ni80Fe20 (111) 50 nm/Al 1.6 nm–O/Co75Fe25 4 nm/Ir22Mn78 10 nm/Ni80Fe20 30 nm were fabricated using UHV sputtering and photolithography process. As the annealing temperature increased up to 250 °C, tunnel magnetoresistance (TMR) ratio at 1 mV bias increased from 28% to 43% for tox = 180 s plasma oxidation and the V±1/2, at which the zero bias TMR value is halved, is +640 mV and−650 mV for positive and negative bias voltages, respectively. The bias-voltage dependence of TMR could be explained in terms of the relationship with V±1/2 and the interface of the ferromagnetic electrode and the Al–O insulating layer. V+1/2, which reflects the bottom ferromagnetic electrode-barrier interface state, changes with plasma oxidation time, while V−1/2, which corresponds to top ferromagnetic electrode-barrier interface, hardly changes.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Np Metals and alloys
81.65.Mq Oxidation
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering
73.63.-b Electronic transport in nanoscale materials and structures
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.35.B- Structure of clean surfaces (and surface reconstruction)

Brillouin light scattering from pumped uniform-precession and low-k magnons in Ni81Fe19

Ward L. Johnson, Sudook A. Kim, Stephen E. Russek, and Pavel Kabos

Appl. Phys. Lett. 86, 102507 (2005); http://dx.doi.org/10.1063/1.1882754 (3 pages) | Cited 5 times

Online Publication Date: 4 March 2005

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A method is presented for performing Brillouin-light-scattering measurements on uniform-precession and low-wave-number (low-k) magnons excited by a microwave magnetic field in opaque magnetic specimens. The optical configuration is similar to that employed in conventional 180° backscattering measurements, except that the incident and specularly reflected beams pass through the collection lens along different parallel paths. Examples of spectra from a Ni81Fe19 film are presented that include separate detection of light scattered from low-k magnons with the same frequency as the uniform precession.
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75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.35.+c Brillouin and Rayleigh scattering; other light scattering
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Ds Spin waves

Change of the barrier potential shape in magnetic tunnel junctions due to an anneal treatment

P. H. P. Koller, H. J. M. Swagten, W. J. M. de Jonge, and R. Coehoorn

Appl. Phys. Lett. 86, 102508 (2005); http://dx.doi.org/10.1063/1.1883324 (3 pages)

Online Publication Date: 4 March 2005

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A very important process step in the fabrication of magnetic tunnel junctions (MTJs) is the application of a modest anneal step in the presence of a high magnetic field. Roughly, a doubling of the magnetoresistance (MR) ratio is commonly observed. We show that both AlOx as well as TaOx MTJs with Co90Fe10 electrodes have similar oxidation time and anneal temperature dependencies of the MR ratios. In both cases, the maximum MR ratio shifts to higher oxidation times with annealing. TaOx MTJs are, in this sense, good model systems. From photoconductance experiments we find that for TaOx MTJs, this shift in maximum MR is accompanied by a similar shift of the zero crossing of the oxidation time dependent barrier asymmetry. This directly supports the point of view that for obtaining the highest MR ratio one should anneal MTJs that would be characterized as “slightly overoxidized” in the as-deposited state. We argue that this result can be understood by a homogenization of the oxygen distribution in the barrier, and∕or a change of the bottom barrier-electrode interface.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Pz Photoconduction and photovoltaic effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
81.65.Mq Oxidation
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