Electronic properties of the itinerant electron antiferromagnet ${\mathrm{NpSn}}_3$ were studied by ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ Mössbauer spectroscopy under pressures up to ∼6.2 GPa. These measurements revealed totally unexpected results: With reduced volume the hyperfine field changes very slightly, but the Néel 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 ${\mathrm{CeAl}}_2$.

• Received 26 February 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.2290