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11 Mar 2002

Volume 80, Issue 10, pp. 1683-1849

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Local contactless measurement of the ordinary and extraordinary Hall effect using near-field microwave microscopy

M. Abu-Teir, F. Sakran, M. Golosovsky, D. Davidov, and A. Frenkel

Appl. Phys. Lett. 80, 1776 (2002); http://dx.doi.org/10.1063/1.1456541 (3 pages) | Cited 3 times

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We report a polarization-sensitive scanning microwave microscope based on a bimodal dielectric resonator with a cross-slit aperture. The microscope operates at ∼26 GHz in the reflection mode and has a subwavelength spatial resolution. It allows contactless mapping of the conductivity tensor, including magnetic-field-induced terms such as the Hall effect. We demonstrate local contactless measurement of the ordinary Hall effect in semiconducting wafers and of the extraordinary Hall effect in thin ferromagnetic Ni films. The latter yields out-of-plane magnetization. The microwave measurements are in good agreement with the dc Hall-effect measurements. © 2002 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
73.61.At Metal and metallic alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
72.20.My Galvanomagnetic and other magnetotransport effects
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Transition from negative magnetoresistance behavior to positive behavior in Co20(Cu1−xGex)80 ribbons

J. He, Z. D. Zhang, J. P. Liu, and D. J. Sellmyer

Appl. Phys. Lett. 80, 1779 (2002); http://dx.doi.org/10.1063/1.1458682 (3 pages) | Cited 1 time

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We report a transition of the giant magnetoresistance (GMR) behavior in nanocrystalline Co20(Cu1−xGex)80 ribbons from negative to positive, as the semiconductor Ge substitutes for the Cu matrix. The growth of the hexagonal Co3Ge2 compound leads to a change of the physical origin of the GMR. The normal spin-dependent transport behavior in the CoCu granular system evolves into Coulomb blockade behavior of electronic tunneling in ribbons with a Co/Co3Ge2/Co junctionlike configuration. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
73.23.Hk Coulomb blockade; single-electron tunneling
75.47.De Giant magnetoresistance

Low voltage I–V characteristics in magnetic tunneling junctions

G. G. Cabrera and N. García

Appl. Phys. Lett. 80, 1782 (2002); http://dx.doi.org/10.1063/1.1433168 (3 pages) | Cited 16 times

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We show that elastic currents, which take into account variations of the tunneling transmission with voltage and a large ratio of majority to minority spin densities of states of the conduction band at the Fermi level, can account for the low voltage current anomalies observed in magnet–oxide–magnet junctions. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
75.47.De Giant magnetoresistance
75.10.Lp Band and itinerant models

Balistic magnetoresistance in nanocontacts electrochemically grown between macro- and microscopic ferromagnetic electrodes

N. García, G. G. Qiang, and I. G. Saveliev

Appl. Phys. Lett. 80, 1785 (2002); http://dx.doi.org/10.1063/1.1459108 (3 pages) | Cited 16 times

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Our results prove the local origin of magnetoresistance in electrochemically deposited Ni nanocontacts. Experiments have been done using a complex setup for both in situ growth and ballistic magnetoresistance (BMR) measurements. Nanocontacts have been grown between two macroscopic Ni wires. In situ experiments with variation of the nanocontact diameter from 3 to 20 nm have been done using the same pair of wires. BMR values from 0.5% to 100% have been observed but no correlation of BMR value with the sample resistance, i.e., with the nanocontact cross section, has been found. These results show that the BMR in the nanometric size contact is determined by local geometrical and magnetic structures near the nanocontact rather than by the contact cross section itself. The hypothesis of existence of the intrinsic nonmagnetic dead layer in the ferromagnetic nanocontact is proposed to account for the BMR properties of the nanometric size contacts. Additionally, we report a BMR value of 200% in a Ni nanocontact (5 nm diameter) electrochemically grown between two nonmagnetic macroscopic gold wires. An external magnetic field has been used during the electrochemical deposition to fix the easy magnetic axis of the deposited Ni layer. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
73.40.Jn Metal-to-metal contacts
73.61.At Metal and metallic alloys
75.50.Cc Other ferromagnetic metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Pq Electrodeposition, electroplating

Quantum-confined magneto-Stark effect in diluted magnetic semiconductor coupled quantum wells

Kai Chang, J. B. Xia, H. B. Wu, S. L. Feng, and F. M. Peeters

Appl. Phys. Lett. 80, 1788 (2002); http://dx.doi.org/10.1063/1.1459491 (3 pages) | Cited 2 times

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The magneto-Stark effect in a diluted magnetic semiconductor (DMS) coupled quantum well (CQW) induced by an in-plane magnetic field is investigate theoretically. Unlike the usual electro-Stark effects, in a DMS CQW the Lorenz force leads to a spatially separated exciton. The in-plane magnetic field can shift the ground state of the magnetoexciton from a zero in-plane center of mass (CM)/momentum to a finite CM momentum, and render the ground state of magnetoexciton stable against radiative recombination due to momentum conservation. © 2002 American Institute of Physics.
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78.67.De Quantum wells
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
71.35.Ji Excitons in magnetic fields; magnetoexcitons
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.Fg Quantum wells

Phase diagram of three contrasting magnetization reversal phases in uniaxial ferromagnetic thin films

Sug-Bong Choe and Sung-Chul Shin

Appl. Phys. Lett. 80, 1791 (2002); http://dx.doi.org/10.1063/1.1457527 (3 pages) | Cited 17 times

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We present an analytical description of a magnetization reversal phase diagram of ferromagnetic thin films that have uniaxial perpendicular anisotropy. The phase equilibrium lines were calculated from a micromagnetic consideration of equilibrium conditions of the wall motion, dendritic growth, and nucleation processes. The phase diagram characterizes well simulated domain evolution patterns: typical domain evolution patterns are predicted accurately in the corresponding phases accompanied by gradual phase transitions across the phase equilibrium lines. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Jk Magnetization reversal mechanisms
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy

Spin polarization contrast observed in GaAs by force-detected nuclear magnetic resonance

Kent R. Thurber, Lee E. Harrell, Raúl Fainchtein, and Doran D. Smith

Appl. Phys. Lett. 80, 1794 (2002); http://dx.doi.org/10.1063/1.1458688 (3 pages) | Cited 12 times

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We applied the technique of force-detected nuclear magnetic resonance to observe 71Ga, 69Ga, and 75As in GaAs. The nuclear spin-lattice relaxation time is 21±5 min for 69Ga at ∼5 K and 4.6 T. We have exploited this long relaxation time to first create and then observe spatially varying nuclear spin polarization within the sample, demonstrating a form of contrast for magnetic resonance force microscopy. Such nuclear spin contrast could be used to indirectly image electron spin polarization in GaAs-based spintronic devices. © 2002 American Institute of Physics.
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76.60.Es Relaxation effects
76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
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