at Low Temperatures*

The temperature dependence of the μSR relaxation rate in SmB₆ exposed to a high transverse magnetic field (TF) was recently shown to exhibit thermally-activated behavior for 4 K < T < 20 K, consistent with the freezing out of a bulk low-energy (~ 1 meV) spin exciton [K. Akintola et al., npj Quantum Materials 3:36 (2018)]. However, a 1 meV magnetic excitation has never been observed in neutron scattering measurements, all of which have been performed on the same floating-zone grown double-isotope ¹⁵⁴Sm¹¹B₆ single crystal. In an attempt to understand why, we have performed zero-field (ZF) and longitudinal-field (LF) μSR measurements on the ¹⁵⁴Sm¹¹B₆ and Al-flux grown SmB₆ single crystals. The μSR signals show greater relaxation in the ¹⁵⁴Sm¹¹B₆ single crystal, and reveal the development of slow and fast relaxing components below T ~ 20 K. The volume fraction of the slower relaxing component grows to ~ 70 % at T = 2 K. While the relaxation rates are smaller, the volume fractions of the two components are similar in the Al-flux grown SmB₆ crystals. This suggests that the source of the two components is intrinsic and originates from spatially distinguishable regions in the sample.