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23 Aug 1999

Volume 75, Issue 8, pp. 1033-1181

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Integrated micromechanical cantilever magnetometry of Ga1−xMnxAs

J. G. E. Harris, D. D. Awschalom, F. Matsukura, H. Ohno, K. D. Maranowski, and A. C. Gossard

Appl. Phys. Lett. 75, 1140 (1999); http://dx.doi.org/10.1063/1.124622 (3 pages) | Cited 33 times

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We have developed a technique for fabricating submicron GaAs micromechanical cantilevers into which lithographically patterned samples grown by molecular beam epitaxy or evaporative deposition are integrated. The torque sensitivity of the 100-nm-thick cantilevers makes them ideal for torsional magnetometry of nanometer-scale, anisotropic samples. We present measurements on samples of the ferromagnetic semiconductor Ga1−xMnxAs at temperatures from 350 mK to 65 K and in fields from 0 to 8 T. By measuring the shift in the resonant frequency of the cantilevers, we demonstrate a moment sensitivity of 3×106 μB at 0.1 T, an improvement of nearly five orders of magnitude upon existing torsional magnetometers. © 1999 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
07.10.Cm Micromechanical devices and systems
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Biased switching of small magnetic particles

R. L. Stamps and B. Hillebrands

Appl. Phys. Lett. 75, 1143 (1999); http://dx.doi.org/10.1063/1.124623 (3 pages) | Cited 24 times

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High-frequency switching of single domain, uniaxial magnetic particles is discussed in terms of transition rates controlled by a small transverse bias field. It is shown that fast switching times can be achieved using bias fields an order of magnitude smaller than the effective anisotropy field. Analytical expressions for the switching time are derived in special cases, and general configurations of practical interest are examined using numerical simulations. © 1999 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials

Effect of tolerance factor and local distortion on magnetic properties of the perovskite manganites

J. P. Zhou, J. T. McDevitt, J. S. Zhou, H. Q. Yin, J. B. Goodenough, Y. Gim, and Q. X. Jia

Appl. Phys. Lett. 75, 1146 (1999); http://dx.doi.org/10.1063/1.124624 (3 pages) | Cited 23 times

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The substitutions of rare earths for La on the magnetic properties of the perovskites La0.7−xRxA0.3MnO3 (0<x<0.7), R=Pr or Gd and A=Ca, Sr, or Ba have shown that small substitution of Pr slightly increases the coercive field Hc and magnetization M, and strongly improves the magnetoresistance (MR) while lowering Tc. On the other hand, the substitution of Gd lowers Hc, M and Tc, however, increases MR of the system La0.7−xGdxSr0.3MnO3 at temperature <Tc. Large differences in the A-site ionic radii rA of the AMnO3 perovskites proved detrimental. The optimal composition has been discussed for the half-metallic ferromagnet of a spin-switch device based on the manganese oxides. © 1999 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Spin-polarized quasiparticle tunnel injection in a YBa2Cu3Oy/Au/Co junction

Kiejin Lee, Wan Wang, Ienari Iguchi, Barry Friedman, Takayuki Ishibashi, and Katsuaki Sato

Appl. Phys. Lett. 75, 1149 (1999); http://dx.doi.org/10.1063/1.124625 (3 pages) | Cited 22 times

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We report the strong suppression of YBa2Cu3Oy (YBCO) supercurrent by injection of spin-polarized quasiparticles (QP) using a cobalt ferromagnetic injector. The injection of spin-polarized QP generates a substantially larger nonequilibrium population as compared with that of an unpolarized injection current. The observed current gain depends on the thickness of Au interlayer (dAu) and is directly related to the nonequilibrium magnetization due to spin relaxation effects. For dAu = 15 nm, the tunnel characteristic a YBCO/Au/Co junction exhibited a zero bias conductance peak, which may be interpreted by spin scattering processes at a ferromagnetic/d-wave superconductor junction. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.72.-h Cuprate superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena

Potentiometric imaging of (La0.7Sr0.3)MnO3 thin films

J. J. Versluijs, F. Ott, and J. M. D. Coey

Appl. Phys. Lett. 75, 1152 (1999); http://dx.doi.org/10.1063/1.124626 (3 pages) | Cited 8 times

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Scanning tunneling potentiometry has been used to simultaneously image the surface topography and map the potential distribution on films of (La0.7Sr0.3)MnO3 deposited on polycrystalline and single crystal MgO substrates. Potential steps in the polycrystalline films coincide with the crystallite boundaries in the film. The grain boundary resistivity varies in the range 3×10−7–3×10−5 Ω cm2, with a typical value of 6×10−6 Ω cm2. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Mm Grain and twin boundaries
73.25.+i Surface conductivity and carrier phenomena
68.55.-a Thin film structure and morphology
68.35.Md Surface thermodynamics, surface energies
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