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Joined 2026-09-21 Message
Incoming links: Spin diffusion length
Specify the magnetoresistance ratio as . Increasing a continuous Cu spacer adds spin-independent series resistance. Even when remains below the spin diffusion length, this dilutes the ratio; spin information need not be destroyed to reduce the percentage signal. In the illustrative two-current resistor model,which decreases as increases. The absolute difference also decreases in this model. At a fixed bias current, the measured voltage contrast is .
For comparable to or greater than the spin diffusion length, additional spin relaxation further suppresses the contrast. At the other extreme an ultrathin or discontinuous Cu layer can introduce direct magnetic coupling or pinholes, preventing a fully antiparallel state. Thickness-dependent interlayer coupling can therefore make the very-thin-spacer trend nonmonotonic; a universal exponential law does not follow from the supplied assumptions.
Two practical approaches retaining Co and NiFe are:
- Improve the spin-selective interfaces: control deposition and intermixing, avoid oxidation or magnetic dead layers, and reduce pinholes and spin-flip defects. The aim is large majority/minority transport asymmetry with low spin-memory loss, rather than merely the smallest total resistance.
- Optimize the Cu thickness and electrical stack: use the thinnest continuous spacer that still allows independent layer reversal and remains well below its spin diffusion length; reduce extraneous contact or lead resistance. This preserves a full antiparallel state and limits spin-independent dilution of the measured magnetoresistance ratio.
Increasing magnetic-layer thickness toward the useful spin-dependent-scattering scale can be another optimization, but growth beyond the relevant spin diffusion scale eventually gives diminishing returns. Merely increasing the bias current increases the readout voltage and possible heating; it does not, by itself, increase the intrinsic giant magnetoresistance ratio.