= Solution
Assume NiFe is the softer layer, with $0<H_{c,\mathrm{NiFe}}<H_{c,\mathrm{Co}}$, and that interlayer coupling is weak enough to permit separate reversal. Starting at large negative $H$, both <magnetizations> point in the same direction and $R=R_P$. During an increasing-field sweep:
* At $H=H_{c,\mathrm{NiFe}}$, NiFe reverses while Co does not: the state is antiparallel and the resistance rises to $R_{AP}$.
* At $H=H_{c,\mathrm{Co}}$, Co also reverses: the state becomes parallel and the resistance returns to $R_P$.
On decreasing $H$ from positive saturation, the high-resistance window instead lies between $-H_{c,\mathrm{Co}}$ and $-H_{c,\mathrm{NiFe}}$. Thus the two sweep directions give displaced rectangular high-resistance windows, not a single reversible resistance peak centered on zero.
\Image[/past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2023/paper-2-spin-valve.png]
{title=Pseudo spin-valve resistance loops, distributed switching and spacer dilution}
{description=Original illustrative curves. Separate coercive fields create an antiparallel window on each sweep. The middle panel isolates switching-field broadening; its retained peak height is not a claim that real roughness leaves the GMR amplitude unchanged.}
{source=paper-2-spin-valve.py}
If Co were the softer layer, the sequence of layer labels would be exchanged. A continuous spacer and sufficiently weak coupling are additional assumptions: negligible surface roughness alone does not guarantee independent switching at every Cu thickness.
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