"From Giant Magneto Resistance in nano-pillars  to spin torque in domain Wall
(an unified approach)" 
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For a long time, spintronic has been synonymous
of giant magnetoresistance (GMR), however many interesting physical effect can
be observed in non collinear magnetic system. Most notably the reverse
phenomenon of GMR the so called Spin Transfer Torque effect (STT) has raised
very important expectation  in the industry (ST-MRAM, tunable current
high-frequency oscillators,.....).
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There exist various approaches  to describe the transport properties of
such magnetic structures, but  most of  them  are in practice  limited to an
oversimplified (1D) descriptions of  the real systems.  We will show how this
limitation can be overcome and present a simple theoretical framework that
permit to describe spin transport properties for real 3D samples with complex
magnetic texture. 
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After a brief description of the formalism we will illustrate its
capability by addressing two problems. Firstly we investigate the GMR in the
current in plane geometry (CIP) and show a new mechanism leading to a mesoscopic
GMR effect.  Secondly we study the Spin Transfer Torque in two non uniform
magnetic system :  a multilayer nano-pillars and  a domain wall. In particular
we address  the so called "field like torque",  also known as the "non-adiabatic
torque" and relate  the latter to the microscopic length  scale of the problem
(experimentally accessible).