Muon spin rotation and relaxation study of the ferromagnetβ-UB2C

Abstract

Magnetic ordering and spin dynamics of $5f$ electrons in ferromagnetic $\ensuremath{\beta}$-UB${}_{2}$C with ${T}_{\mathrm{C}}=74.5$ K have been investigated by muon spin rotation and relaxation ($\ensuremath{\mu}$SR). The experimental data indicate a slowing down of the spin fluctuations of the U moments on approaching ${T}_{\mathrm{C}}$ from the paramagnetic regime. In the ferromagnetic state, a spontaneous muon spin precession with a single frequency is observed, characteristic of a quasi-static mean magnetic field at a single muon site. The damping rate of the precessing signal is essentially of static origin, and it shows a dip at around 40 K, close to the temperature where the magnetic specific heat and the temperature derivative of the resistivity reveal an anomaly. Therefore, these anomalies are mainly related to the static component of 5 $f$ electrons. The spin-lattice relaxation rate measured in the ferromagnetic phase seems to probe the spin dynamics of the itinerant electronic rate. This component remains finite down to the lowest measured temperature; therefore, it is characterized by an appreciable density of magnetic fluctuations at extremely low energy. Hence, as for UGe${}_{2}$, the $5f$ electrons in $\ensuremath{\beta}$-UB${}_{2}$C are suggested to exist in two different substates of localized and itinerant nature.