  In most superconductors electrons form Cooper pairs in a spin-singlet state
mediated by either phonons or by long-range interactions such as spin
fluctuations. The superconductor UTe$_2$ is a rare material wherein electrons
are believed to form pairs in a unique spin-triplet state with potential
topological properties. While spin-triplet pairing may be mediated by
ferromagnetic or antiferromagnetic fluctuations, experimentally, the magnetic
properties of UTe$_2$ are unclear. By way of muon spin rotation/relaxation
($\mu$SR) measurements on independently grown UTe$_2$ single crystals we
demonstrate the existence of magnetic clusters that gradually freeze into a
disordered spin frozen state at low temperatures. Our findings suggest that
inhomogeneous freezing of magnetic clusters is linked to the ubiquitous
residual linear term in the temperature dependence of the specific heat ($C$)
and the low-temperature upturn in $C/T$ versus $T$. The omnipresent magnetic
inhomogeneity has potential implications for experiments aimed at establishing
the intrinsic low-temperature properties of UTe$_2$.
