298 research outputs found
Thermal switching of indirect interlayer exchange in magnetic multilayers
We propose a magnetic multilayer layout, in which the indirect exchange
coupling (IEC also known as RKKY) can be switched on and off by a slight change
in temperature. We demonstrate such on/off IEC switching in a Fe/Cr/FeCr-based
system and obtain thermal switching widths as small as 10--20~K, essentially in
any desired temperature range, including at or just above room temperature.
These results add a new dimension of tunable thermal control to IEC in magnetic
nanostructures, highly technological in terms of available materials and
operating physical regimes.Comment: 3 figures, Supplementary Inf
Ferromagnetic resonance and interlayer exchange coupling in magnetic multilayers with compositional gradients
Ferromagnetic resonance (FMR) in magnetic multilayers of type F1/f/F2, where
two strongly ferromagnetic layers F1 and F2 are separated by a weakly magnetic
spacer f with a compositional gradient along its thickness, is investigated.
The method allows to detect the weak signal from the spacer in additional to
the more pronounced and readily measured signal from the outer
strongly-magnetic layers, and thereby study the properties of the spacer as
well as the interlayer exchange interaction it mediates. Variable temperature
FMR measurements, especially near the relevant Curie points, reveal a rich set
of properties of the exchange interactions in the system. The obtained results
are useful for designing and optimizing nanostructures with
thermally-controlled magnetic properties.Comment: 6 pages, 3 figure
Temperature-controlled interlayer exchange coupling in strong/weak ferromagnetic multilayers: a thermo-magnetic Curie-switch
We investigate a novel type of interlayer exchange coupling based on driving
a strong/weak/strong ferromagnetic tri-layer through the Curie point of the
weakly ferromagnetic spacer, with the exchange coupling between the strongly
ferromagnetic outer layers that can be switched, on and off, or varied
continuously in magnitude by controlling the temperature of the material. We
use Ni-Cu alloy of varied composition as the spacer material and model the
effects of proximity-induced magnetism and the interlayer exchange coupling
through the spacer from first principles, taking into account not only thermal
spin-disorder but also the dependence of the atomic moment of Ni on the
nearest-neighbor concentration of the non-magnetic Cu. We propose and
demonstrate a gradient-composition spacer, with a lower Ni-concentration at the
interfaces, for greatly improved effective-exchange uniformity and
significantly improved thermo-magnetic switching in the structure. The reported
magnetic multilayer materials can form the base for a variety of novel magnetic
devices, such as sensors, oscillators, and memory elements based on
thermo-magnetic Curie-switching in the device.Comment: 15 pages, 5 figure
Precise and ultrafast molecular sieving through graphene oxide membranes
There has been intense interest in filtration and separation properties of
graphene-based materials that can have well-defined nanometer pores and exhibit
low frictional water flow inside them. Here we investigate molecular permeation
through graphene oxide laminates. They are vacuum-tight in the dry state but,
if immersed in water, act as molecular sieves blocking all solutes with
hydrated radii larger than 4.5A. Smaller ions permeate through the membranes
with little impedance, many orders of magnitude faster than the diffusion
mechanism can account for. We explain this behavior by a network of
nanocapillaries that open up in the hydrated state and accept only species that
fit in. The ultrafast separation of small salts is attributed to an 'ion
sponge' effect that results in highly concentrated salt solutions inside
graphene capillaries
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