μSR study of evolution of time-reversal symmetry in the superconducting state of dilute Nd substitution in Pr_1-xNd_xOs₄Sb₁₂

The Pr-rich end of the alloy series Pr_1−xNd_xOs₄Sb₁₂ has been studied using muon spin rotation and relaxation. The end compound PrOs₄Sb₁₂ is an unconventional heavy-fermion superconductor, which exhibits a spontaneous magnetic field in the superconducting phase associated with broken time-reversal symmetry (TRS). However, with a very low concentration of Nd (x ≥ 0.05), no such spontaneous field is observed, indicating that TRS has been recovered. The superfluid density determined from the vortex-lattice field distribution is insensitive to Nd concentration for x ≤ 0.2. No Nd³⁺ static magnetism, ordered or disordered, is found down to the lowest temperatures of measurement.