The interplay between
fluctuations of the local structure and magnetic
interactions is of great importance for phenomena like superconductivity,
colossal magnetoresistance, and frustrated magnetism. Such local distortions
are often subtle and difficult to probe. The metallic MnAs1–x
P
x
(x = 0.06, 0.12, 0.18) solid solution represents a sensitive model
system, currently analyzed by variable-temperature X-ray total scattering
(TS). A second-order transition (Pnma to P63/mmc) occurs on heating,
intimately coupled to magnetic ordering at low temperatures and a
temperature-induced low- to high-spin transition for manganese. Intrinsic
compositional fluctuations along with a particular magneto-volumetric
coupling to low- and high-spin like states triggers formation of local
high-symmetry nanosized domains in an orthorhombically deformed matrix
that eventually converts globally into a high-temperature hexagonal
arrangement. These features are only traced by TS analyses, whereas
diffraction provides a regular second-order transition with, e.g.,
cationic displacements defined by Rietveld analysis acting as order
parameter. The coexistence model provides good fits of the TS data
and, on average, translates nicely into a continuous V(T) thermal expansion relation with maximum expansivity
in the range where the TS data shows the largest difference between
local (<20 Å) and intermediate-range (20–80 Å)
structures. The degree of local distortions, Mn(As, P)6 octahedra inclusive, is a result of volume-dependent electronic
properties as well as magnetic interactions. This study demonstrates
how X-ray TS can conveniently give essential insights into the local
symmetry fluctuations from the perspective of strong magnetic interactions.