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12 Nov 2001

Volume 79, Issue 20, pp. 3215-3366

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Promising ferromagnetic Ni–Co–Al shape memory alloy system

K. Oikawa, L. Wulff, T. Iijima, F. Gejima, T. Ohmori, A. Fujita, K. Fukamichi, R. Kainuma, and K. Ishida

Appl. Phys. Lett. 79, 3290 (2001); http://dx.doi.org/10.1063/1.1418259 (3 pages) | Cited 157 times

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A system of ferromagnetic β phase Ni–Co–Al alloys with an ordered B2 structure that exhibits the shape memory effect has been developed. The alloys of this system within the composition range Ni (30–45 at. %) Co–(27–32 at. %) Al, undergo a paramagnetic/ferromagnetic transition as well as a thermoelastic martensitic transformation from the β to the β′(L10) phase. The Curie and the martensitic start temperatures in the β phase can be controlled independently to fall within the range of 120–420 K. The specimens from some of the alloys undergoing martensitic transformation from ferromagnetic β phase to ferromagnetic β′ phase are accompanied by the shape memory effect. These ferromagnetic shape memory alloys hold great promise as new smart materials. © 2001 American Institute of Physics.
Show PACS
81.30.Kf Martensitic transformations
81.05.Bx Metals, semimetals, and alloys
75.50.Cc Other ferromagnetic metals and alloys
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order

Fragmentation of cobalt layers in Co/Cu multilayers monitored by magnetic and magnetoresistive measurements

F. Spizzo, E. Angeli, D. Bisero, P. Vavassori, and F. Ronconi

Appl. Phys. Lett. 79, 3293 (2001); http://dx.doi.org/10.1063/1.1418023 (3 pages) | Cited 14 times

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We have monitored the structural evolution of Co(tCo)/Cu(4×tCo) multilayers when tCo ranges from 12 to 2 Å. The investigation has been performed by studying their magnetization and giant magnetoresistance, since these properties are complementary in providing information about the structure of the magnetic species into the samples. In particular, in the intermediate range of thickness, we observed no correspondence between magnetic and magnetoresistive behavior. Finally, at sufficiently low thickness, the samples exhibit noninteracting superparamagnetic features. This kind of evolution has been ascribed to the progressive fragmentation of Co layers. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.De Giant magnetoresistance
68.65.Ac Multilayers

In situ magnetoelastic coupling and stress-evolution studies of epitaxial Co35Pd65 alloy films in the monolayer regime

Jong-Ryul Jeong, Jonggeol Kim, Jeong-Won Lee, Sang-Koog Kim, and Sung-Chul Shin

Appl. Phys. Lett. 79, 3296 (2001); http://dx.doi.org/10.1063/1.1418444 (3 pages) | Cited 11 times

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We report in situ measurements of magnetoelastic coupling, B2, and stress, σ, in Co35Pd65 alloy films epitaxially grown on a Cu/Si(001) substrate in a thickness range of 1–10 ML by means of a highly sensitive optical deflection-detecting system. It was found that the value of B2 increases from 0.72×107 J/m3 at 2 ML to 3.31×107 J/m3 at 10 ML. A second-order strain correction of B2 = Bb+C1ϵ+C2ϵ2 rather than a first-order one of B2 = Bb+C1ϵ provides a better fit for the observed behavior of B2 versus film strain, ϵ, where Bb is the bulk value. The relationship between B2 and ϵ observed in the present study reveals that the second-order correction is crucial for understanding the dependence of B2 on ϵ in an ultrathin regime. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
68.60.Bs Mechanical and acoustical properties
75.50.Cc Other ferromagnetic metals and alloys

Significant reduction of the microwave surface resistance of MgB2 films by surface ion milling

Sang Young Lee, J. H. Lee, Jung Hun Lee, J. S. Ryu, J. Lim, S. H. Moon, H. N. Lee, H. G. Kim, and B. Oh

Appl. Phys. Lett. 79, 3299 (2001); http://dx.doi.org/10.1063/1.1418026 (3 pages) | Cited 24 times

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The microwave surface resistance RS of MgB2 films with the zero-resistance temperature of ∼39 K was measured at 8.0–8.5 GHz. The MgB2 films were prepared by deposition of boron films on c-cut sapphire, followed by annealing in a magnesium vapor environment. The RS appeared significantly reduced by ion milling of the as-grown MgB2 film surface, with the observed RS of ∼0.8 mΩ at 24 K for an ion-milled MgB2 film as small as 1/15 of the value for the corresponding as-grown MgB2 film. The reduced RS of the ion-milled MgB2 films is attributed to the effects of the Mg-rich metallic layer existing at the surfaces of the as-grown MgB2 films. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.72.-h Cuprate superconductors
81.65.-b Surface treatments

Giant magnetocaloric effect of MnAs1−xSbx

H. Wada and Y. Tanabe

Appl. Phys. Lett. 79, 3302 (2001); http://dx.doi.org/10.1063/1.1419048 (3 pages) | Cited 350 times

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A giant magnetocaloric effect was found in MnAs, which undergoes a first-order ferromagnetic to paramagnetic transition at 318 K. The magnetic entropy change caused by a magnetic field of 5 T is as large as 30 J/K kg at the maximum value, which exceeds that of conventional magnetic refrigerant materials by a factor of 2–4. The adiabatic temperature change reaches 13 K in a field change of 5 T. The substitution of 10% Sb for As reduces the thermal hysteresis and lowers the Curie temperature to 280 K, while the giant magnetocaloric properties are retained. © 2001 American Institute of Physics.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Spin-polarized transport in GaMnAs multilayers

L. Loureiro da Silva, M. A. Boselli, I. C. da Cunha Lima, X. F. Wang, and A. Ghazali

Appl. Phys. Lett. 79, 3305 (2001); http://dx.doi.org/10.1063/1.1415407 (3 pages) | Cited 13 times

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The spin-dependent mobility for the lateral transport of the hole gas in a GaMnAs/GaAs heterostructure containing several metallic-like ferromagnetic layers is calculated. The electronic structure is obtained self-consistently taking into account the direct Coulomb Hartree and exchange-correlation terms, besides the sp–d exchange interaction with the Mn magnetic moments.© 2001 American Institute of Physics.
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72.25.Dc Spin polarized transport in semiconductors
73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions

Microelectromagnets for the control of magnetic nanoparticles

C. S. Lee, H. Lee, and R. M. Westervelt

Appl. Phys. Lett. 79, 3308 (2001); http://dx.doi.org/10.1063/1.1419049 (3 pages) | Cited 91 times

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A microelectromagnet matrix and a ring trap that position and control magnetic nanoparticles are demonstrated. They consist of multiple layers of lithographically defined Au wires separated by transparent, insulating polyimide layers on sapphire substrates. Magnetic field patterns produced by these devices allow microscopically precise control and manipulation of magnetic nanoparticles. A microelectromagnet matrix produces single or multiple peaks in the magnetic field magnitude, which trap, move, and rotate magnetic nanoparticles, as well as electromagnetic fields to probe and detect particles. Microelectromagnets are new tools with which to study and manipulate nanoparticles and biological entities. © 2001 American Institute of Physics.
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07.55.Db Generation of magnetic fields; magnets
75.50.Tt Fine-particle systems; nanocrystalline materials
06.60.Sx Positioning and alignment; manipulating, remote handling
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
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