= Solution
Along the \b[easy axis], expect an approximately rectangular loop: after saturation the remanent <magnetization> is close to $\pm M_s$, and reversal occurs near $\pm H_c$ through <nucleation> and domain-wall motion. Permalloy is magnetically soft, so $H_c$ is ordinarily small, although defects and growth conditions set its actual value.
\Image[/past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2017/paper-2-permalloy-loops.png]
{title=Easy-axis switching and hard-axis rotation for an idealized uniaxial thin film}
{source=paper-2-permalloy-loops.py}
The axes are $M$ in $\mathrm{A\,m^{-1}}$ and applied $\mu_0H$ in $\mathrm{mT}$. $M_s,H_c,H_k$ are symbolic because their measured values are not supplied. The $50\,\mathrm{mT}$ deposition field establishes an axis; it is not the measured coercive or anisotropy field.
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