  Strongly correlated quantum solids are characterized by an inherently
granular electronic fabric, with spatial patterns that can span multiple length
scales in proximity to a critical point. Here, we used a resonant magnetic
X-ray scattering nanoprobe with sub-100 nm spatial resolution to directly
visualize the texture of antiferromagnetic domains in NdNiO$_3$. Surprisingly,
our measurements revealed a highly textured magnetic fabric, which is shown to
be robust and nonvolatile even after thermal erasure across its ordering
($T_{N\acute{e}el}$) temperature. The scale-free distribution of
antiferromagnetic domains and its non-integral dimensionality point to a
hitherto-unobserved magnetic fractal geometry in this system. These
scale-invariant textures directly reflect the continuous nature of the magnetic
transition and the proximity of this system to a critical point. The present
study not only exposes the near-critical behavior in rare earth nickelates but
also underscores the potential for novel X-ray scattering nanoprobes to image
the multiscale signatures of criticality near a critical point.
