236 research outputs found
Exchange coupling and magnetoresistance in CoFe/NiCu/CoFe spin-valves near the Curie point of the spacer
Thermal control of exchange coupling between two strongly ferromagnetic
layers through a weakly ferromagnetic Ni-Cu spacer and the associated
magnetoresistance is investigated. The spacer, having a Curie point slightly
above room temperature, can be cycled between its paramagnetic and
ferromagnetic states by varying the temperature externally or using joule
heating. It is shown that the giant magnetoresistance vanishes due to a strong
reduction of the mean free path in the spacer at above ~30 % Ni concentration
-- before the onset of ferromagnetism. Finally, a device is proposed and
demonstrated which combines thermally controlled exchange coupling and large
magnetoresistance by separating the switching and the read out elements.Comment: 4 pages, 4 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
Antiferromagnet-mediated interlayer exchange: hybridization versus proximity effect
We investigate the interlayer coupling between two thin ferromagnetic (F)
films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and
show how it transitions between different regimes on changing the AF thickness.
Employing layer-selective Kerr magnetometry and ferromagnetic-resonance
techniques in a complementary manner enables us to distinguish between three
functionally distinct regimes of such ferromagnetic interlayer coupling. The F
layers are found to be individually and independently exchange-biased for thick
FeMn spacers - the first regime of no interlayer F-F* coupling. F-F* coupling
appears on decreasing the FeMn thickness below 9 nm. In this second regime
found in structures with 6.0-9.0 nm thick FeMn spacers, the interlayer coupling
exists only in a finite temperature interval just below the effective N\'eel
temperature of the spacer, which is due to magnon-mediated exchange through the
thermally softened antiferromagnetic spacer, vanishing at lower temperatures.
The third regime, with FeMn thinner than 4 nm, is characterized by a much
stronger interlayer coupling in the entire temperature interval, which is
attributed to a magnetic-proximity induced ferromagnetic exchange. These
experimental results, spanning the key geometrical parameters and thermal
regimes of the F*/AF/F nanostructure, complemented by a comprehensive
theoretical analysis, should broaden the understanding of the interlayer
exchange in magnetic multilayers and potentially be useful for applications in
spin-thermionics.Comment: 14 pages, 9 figure
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