1,096 research outputs found
Proximity-induced density-of-states oscillations in a superconductor/strong-ferromagnet system
We have measured the evolution of the tunneling density of states (DOS) in
superconductor/ferromagnet (S/F) bilayers with increasing F-layer thickness,
where F in our experiment is the strong ferromagnet Ni. As a function of
increasing Ni thickness, we detect multiple oscillations in the DOS at the
Fermi energy from differential conductance measurements. The features in the
DOS associated with the proximity effect change from normal to inverted twice
as the Ni thickness increases from 1 to 5 nm.Comment: 4 pages, 4 figure
Switching Current vs. Magnetoresistance in Magnetic Multilayer Nanopillars
We study current-driven magnetization switching in nanofabricated magnetic
trilayers, varying the magnetoresistance in three different ways. First, we
insert a strongly spin-scattering layer between the magnetic trilayer and one
of the electrodes, giving increased magnetoresistance. Second, we insert a
spacer with a short spin-diffusion length between the magnetic layers,
decreasing the magnetoresistance. Third, we vary the angle between layer
magnetizations. In all cases, we find an approximately linear dependence
between magnetoresistance and inverse switching current. We give a qualitative
explanation for the observed behaviors, and suggest some ways in which the
switching currents may be reduced.Comment: 3 pages, 4 figure
Neutron skin uncertainties of Skyrme energy density functionals
Background: Neutron-skin thickness is an excellent indicator of isovector
properties of atomic nuclei. As such, it correlates strongly with observables
in finite nuclei that depend on neutron-to-proton imbalance and the nuclear
symmetry energy that characterizes the equation of state of neutron-rich
matter. A rich worldwide experimental program involving studies with rare
isotopes, parity violating electron scattering, and astronomical observations
is devoted to pinning down the isovector sector of nuclear models. Purpose: We
assess the theoretical systematic and statistical uncertainties of neutron-skin
thickness and relate them to the equation of state of nuclear matter, and in
particular to nuclear symmetry energy parameters. Methods: We use the nuclear
superfluid Density Functional Theory with several Skyrme energy density
functionals and density dependent pairing. To evaluate statistical errors and
their budget, we employ the statistical covariance technique. Results: We find
that the errors on neutron skin increase with neutron excess. Statistical
errors due to uncertain coupling constants of the density functional are found
to be larger than systematic errors, the latter not exceeding 0.06 fm in most
neutron-rich nuclei across the nuclear landscape. The single major source of
uncertainty is the poorly determined slope L of the symmetry energy that
parametrizes its density dependence. Conclusions: To provide essential
constraints on the symmetry energy of the nuclear energy density functional,
next-generation measurements of neutron skins are required to deliver precision
better than 0.06 fm.Comment: 5 pages, 4 figure
Measurement of spin memory lengths in PdNi and PdFe ferromagnetic alloys
Weakly ferromagnetic alloys are being used by several groups in the study of
superconducting/ferromagnetic hybrid systems. Because spin-flip and spin-orbit
scattering in such alloys disrupt the penetration of pair correlations into the
ferromagnetic material, it is desirable to have a direct measurement of the
spin memory length in such alloys. We have measured the spin memory length at
4.2 K in sputtered Pd0.88Ni0.12 and Pd0.987Fe0.013 alloys using methods based
on current-perpendicular-to-plane giant magnetoresistance. The alloys are
incorporated into hybrid spin valves of various types, and the spin memory
length is determined by fits of the Valet-Fert spin-transport equations to data
of magnetoresistance vs. alloy thickness. For the case of PdNi alloy, the
resulting values of the spin memory length are lsf(PdNi) = 2.8 +/- 0.5 nm and
5.4 +/- 0.6 nm, depending on whether or not the PdNi is exchange biased by an
adjacent Permalloy layer. For PdFe, the spin memory length is somewhat longer,
lsf(PdFe) = 9.6 +/- 2 nm, consistent with earlier measurements indicating lower
spin-orbit scattering in that material. Unfortunately, even the longer spin
memory length in PdFe may not be long enough to facilitate observation of
spin-triplet superconducting correlations predicted to occur in
superconducting/ferromagnetic hybrid systems in the presence of magnetic
inhomogeneity.Comment: 7 pages, 8 figure
Manipulating Current-Induced Magnetization Switching
We summarize our recent findings on how current-driven magnetization
switching and magnetoresistance in nanofabricated magnetic multilayers are
affected by varying the spin-scattering properties of the non-magnetic spacers,
the relative orientations of the magnetic layers, and spin-dependent scattering
properties of the interfaces and the bulk of the magnetic layers. We show how
our data are explained in terms of current-dependent effective magnetic
temperature.Comment: 6 pages, 6 figures, submitted to MMM'04 proceeding
Current-Driven Magnetic Excitations in Permalloy-Based Multilayer Nanopillars
We study current-driven magnetization switching in nanofabricated
Ni84Fe16/Cu/Ni84Fe16 trilayers at 295 K and 4.2 K. The shape of the hysteretic
switching diagram at low magnetic field changes from 295 K to 4.2 K. The
reversible behavior at higher field involves two phenomena, a threshold current
for magnetic excitations closely correlated with the switching current, and a
peak in differential resistance characterized by telegraph noise, with average
period that decreases exponentially with current and shifts with temperature.
We interpret both static and dynamic results at 295 K and 4.2 K in terms of
thermal activation over a potential barrier, with a current dependent effective
magnetic temperature.Comment: 4 pages, 4 Figure
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