Mössbauer and magnetization studies of the Np M 2 Si 2 ( M = C r , M n , F e , C o , N i , C u ) systems

Magnetization and $^{237}\mathrm{Np}$ M\"ossbauer studies of the tetragonal $\mathrm{Np}{M}_{2}{\mathrm{Si}}_{2}$ intermetallic compounds were performed. The compounds exhibit a wide variety of magnetic phenomena. Np${\mathrm{Mn}}_{2}$${\mathrm{Si}}_{2}$ orders ferromagnetically above 300 K, and has a magnetic hyperfine interaction of 1840(50) MHz at 4.2 K. All other compounds order antiferromagnetically. The N\'eel points and the magnetic hyperfine interaction in saturation of the $\mathrm{Np}{M}_{2}{\mathrm{Si}}_{2}$ compounds are 73(3), 87(3), 42(4), 33(3), 34(3) K and 2800(50), 2535(50), 2300(50), 1730(50), 3430(50) MHz for $M=\mathrm{C}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{F}\mathrm{e},\phantom{\rule{0ex}{0ex}}\mathrm{C}\mathrm{o},\phantom{\rule{0ex}{0ex}}\mathrm{N}\mathrm{i},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{C}\mathrm{u}$, respectively. In Np${\mathrm{Cu}}_{2}$${\mathrm{Si}}_{2}$, the magnetic phase transition is of the first order.