Localized properties of the itinerant 5f-electron antiferromagnet NpSn3

Electronic properties of the itinerant electron antiferromagnet ${\mathrm{NpSn}}_{3}$ were studied by $^{237}\mathrm{Np}$ M\"ossbauer spectroscopy under pressures up to \ensuremath{\sim}6.2 GPa. These measurements revealed totally unexpected results: With reduced volume the hyperfine field changes very slightly, but the N\'eel temperature increases strongly. Such a behavior is typical for localized 5f electrons. We propose that ${\mathrm{NpSn}}_{3}$ should be viewed as a concentrated Kondo system, similar to ${\mathrm{CeAl}}_{2}$.