  The performance of permanent magnets is intricately tied to their magnetic
hysteresis loop. In this study, we investigate the heavy-fermion ferromagnet
CeAgSb$_2$ through magnetization measurements under uniaxial stress. We observe
a 2400 % increase in magnetic coercivity with just a modest stress of
approximately 1 kbar. This effect persists even after pressure release,
attributable to stress-induced defects that efficiently pin domain walls. Other
magnetic properties such as ordering temperature and saturation moment exhibit
only weak pressure dependencies and display full reversibility. Our findings
offer a promising route for increasing coercive field strength and enhancing
the energy product in ferromagnetic materials and are potentially applicable to
a broad spectrum of commercial or emerging magnetic applications.
