= Solution
Write the descending and ascending switching fields as $H_-$ and $H_+$. The <exchange bias> loop centre and <magnetic coercivity> half-width are
$$
\boxed{H_E=\frac{H_++H_-}{2},\qquad H_c=\frac{H_+-H_-}{2}.}
$$
With <exchange bias>, a field-cooled bilayer has $H_E\ne0$, often a shift opposite to the cooling field for the conventional negative-bias case shown in the diagram. The sign is not universal; it depends on interfacial coupling and preparation. A simple rigid-pinning estimate is $H_E\sim-J_{\rm int}/(\mu_0M_st_F)$.
Cooling farther below the blocking range usually strengthens antiferromagnetic anisotropy and suppresses thermal relaxation, so the magnitude of the shift and often the coercive width grow. Close to or above the blocking <temperature> the shift disappears; the blocking <temperature> can be below $T_N$. Repeated cycling can rearrange interfacial spins and reduce the bias, and the two reversal branches can acquire different shapes. Thus increasing low-temperature asymmetry is a common tendency, not a guaranteed monotonic law for every interface.
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