  Thermal equilibrium properties of nanoscale systems deviate from standard
macroscopic predictions due to a non-negligible coupling to the environment.
For anisotropic three-dimensional materials, we derive the mean force
corrections to the equilibrium state of a classical spin vector. The result is
valid at arbitrary coupling strength. Specifically, we consider cubic,
orthorhombic, and monoclinic symmetries, and compare their spin expectation
values as a function of temperature. We underpin the correctness of the mean
force state by evidencing its match with the steady state of the simulated
non-Markovian spin dynamics. The results show an explicit dependence on the
symmetry of the confining material. In addition, some coupling symmetries show
a spin alignment transition at zero temperature. Finally, we quantify the work
extraction potential of the mean force-generated inhomogeneities in the energy
shells. Such inhomogeneities constitute a classical equivalent to quantum
coherences.
