Biomedical subjects

Arne Brataas

Publications and source records attributed to Arne Brataas.

10 recordsLinked to original sources

PubMed2006

Voltage generation by ferromagnetic resonance at a nonmagnet to ferromagnet contact.

A ferromagnet can resonantly absorb rf radiation to sustain a steady precession of the magnetization around an internal or applied magnetic field. We show that, under these ferromagnetic resonance conditions, a dc voltage is generated at a normal-metal electric contact to a ferromagnet with spin-flip scattering. The spin dynamics in the nonmagnetic region is accounted for by a frequency-dependent renormalization of the interface conductances. This mechanism allows sensing of time-dependent magnetizations by established dc electronic techniques.

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PubMed2006

Intrinsic domain-wall resistance in ferromagnetic semiconductors.

Transport through zinc blende magnetic semiconductors with magnetic domain walls is studied theoretically. We show that these magnetic domain walls have an intrinsic resistance due to the effective hole spin-orbit interaction. The intrinsic resistance is independent of the domain-wall shape and width and survives the adiabatic limit. For typical parameters, the intrinsic domain-wall resistance is comparable to the Sharvin resistance and should be experimentally measurable.

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PubMed2005

Magnetization noise in magnetoelectronic nanostructures.

By scattering theory we show that spin current noise in normal electric conductors in contact with nanoscale ferromagnets increases the magnetization noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in the spin current is related to the increased Gilbert damping due to spin pumping, in accordance with the fluctuation-dissipation theorem. Spin current shot noise in the presence of an applied bias is the dominant contribution to the magnetization noise at low temperatures.

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PubMed2005

Nanomechanical magnetization reversal.

The dynamics of the ferromagnetic order parameter in thin magnetic films is strongly affected by the magnetomechanical coupling at certain resonance frequencies. By solving the equation of motion of the coupled mechanical and magnetic degrees of freedom we show that the magnetic field induced magnetization switching can be strongly accelerated by the lattice and illustrate the possibility of magnetization reversal by mechanical actuation.

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PubMed2004

Giant fluctuations of superconducting order parameter in ferromagnet-superconductor single-electron transistors.

Spin dependent transport in a ferromagnet-superconductor single-electron transistor is studied theoretically taking into account spin accumulation, spin relaxation, gap suppression, and charging effects. A strong dependence of the gap on the magnetic state of the electrodes is found, which gives rise to a magnetoresistance of up to 100%. We predict that fluctuations of the spin accumulation can play such an important role as to cause the island to fluctuate between the superconducting and normal states. Furthermore, the device exhibits a nearly complete gate-controlled spin-valve effect.

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PubMed2004

Spin and charge pumping by ferromagnetic-superconductor order parameters.

We study transport in ferromagnetic-superconductor/normal-metal systems. It is shown that charge and spin currents are pumped from ferromagnetic superconductors into adjacent normal metals by adiabatic changes in the order parameters induced by external electromagnetic fields. Spin and charge pumping identify the symmetry of the superconducting order parameter, e.g., singlet pairing or triplet pairing with opposite or equal spin pairing. Consequences for ferromagnetic-resonance experiments are discussed.

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PubMed2004

Dynamic ferromagnetic proximity effect in photoexcited semiconductors.

The spin dynamics of photoexcited carriers in semiconductors in contact with a ferromagnet is treated theoretically and compared with time-dependent Faraday rotation experiments. The long-time response of the system is found to be governed by the first tens of picoseconds in which the excited plasma interacts strongly with the intrinsic interface between the semiconductor and the ferromagnet in spite of the existence of a Schottky barrier in equilibrium.

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PubMed2003

Magnetoelectronic spin echo.

We predict a spin echo in electron transport through layered ferromagnetic-normal-ferromagnetic metal structures: whereas a spin current polarized perpendicular to the magnetization direction decays when traversing a single homogeneous ferromagnet on the scale of the ferromagnetic spin-coherence length, it partially reappears by adding a second identical but antiparallel ferromagnet. This reentrant transverse spin current resembles the spin-echo effect in the magnetization of nuclei under pulsed excitations. We propose an experimental setup to measure the spin echo.

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PubMed2003

Dynamic exchange coupling in magnetic bilayers.

A long-range dynamic interaction between ferromagnetic films separated by normal-metal spacers is reported, which is communicated by nonequilibrium spin currents. It is measured by ferromagnetic resonance and explained by an adiabatic spin-pump theory. In such a resonance the spin-pump mechanism of spatially separated magnetic moments leads to an appreciable increase in the resonant linewidth when the resonance fields are well apart, and results in a dramatic linewidth narrowing when the resonant fields approach each other.

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PubMed2002

Enhanced gilbert damping in thin ferromagnetic films.

The precession of the magnetization of a ferromagnet is shown to transfer spins into adjacent normal metal layers. This "pumping" of spins slows down the precession corresponding to an enhanced Gilbert damping constant in the Landau-Lifshitz equation. The damping is expressed in terms of the scattering matrix of the ferromagnetic layer, which is accessible to model and first-principles calculations. Our estimates for permalloy thin films explain the trends observed in recent experiments.

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