Magnetic hyperfine interaction inCeMn2Ge2andCeMn2Si2measured by perturbed angular correlation spectroscopy

Abstract

Time differential perturbed $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ angular correlation technique has been used to measure the magnetic hyperfine field at both Mn and Ce atom sites in ${\mathrm{CeMn}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{CeMn}}_{2}{\mathrm{Si}}_{2}$ intermetallic compounds. The probe nucleus ${}^{111}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{In}}}^{111}\mathrm{Cd}$ was used to investigate the hyperfine interaction at Mn sites, while the ${}^{140}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{La}}}^{140}\mathrm{Ce}$ was used to measure the magnetic hyperfine field at Ce. Present measurements cover the temperature range from 10 to 460 K in both compounds. Measurements with ${}^{111}\mathrm{Cd}$ probe show pure electric quadrupole interactions above 420 K in both compounds and a combined magnetic dipole and electric quadrupole interaction below respective magnetic transition temperatures. While the temperature dependence of the hyperfine field at ${}^{111}\mathrm{Cd}$ on Mn site in the ${\mathrm{CeMn}}_{2}{\mathrm{Si}}_{2}$ showed a standard behavior for an antiferromagnetic compound below ${T}_{N}\ensuremath{\approx}408\mathrm{K},$ the temperature dependence of magnetic hyperline field (MHF) in ${\mathrm{CeMn}}_{2}{\mathrm{Ge}}_{2}$ showed a transition from ferromagnetic to antiferromagnetic phase at around 320 K and from antiferromagnetic to paramagnetic phase at 420 K. No hyperfine field was observed at ${}^{140}\mathrm{Ce}$ in ${\mathrm{CeMn}}_{2}{\mathrm{Si}}_{2}$ in the temperature range from 10 K to 400 K. A unique and well-defined magnetic interaction is observed at Ce sites in ${\mathrm{CeMn}}_{2}{\mathrm{Ge}}_{2}$ below 320 K, corresponding to a ferromagnetic ordering of Mn moments. The temperature dependence of MHF, however, shows a sharp deviation from an expected Brillouin-like behavior for temperatures below 120 K. The additional magnetic interaction is believed to result from the polarization of Ce spin moments induced by the magnetic field from Mn moments.