  The standard approach to realize a spin liquid state is through magnetically
frustrated states, relying on ingredients such as the lattice geometry,
dimensionality, and magnetic interaction type of the spins. While Heisenberg
spins on a pyrochlore lattice with only antiferromagnetic nearest neighbors
interactions are theoretically proven disordered, spins in real systems
generally include longer-range interactions. The spatial correlations at longer
distances typically stabilize a long-range order rather than enhancing a spin
liquid state. Both states can, however, be destroyed by short-range static
correlations introduced by chemical disorder. Here, using disorder-free
specimens with a clear long-range antiferromagnetic order, we refine the spin
structure of the Heisenberg spinel ZnFe2O4 through neutron magnetic
diffraction. The unique wave vector (1, 0, 1/2) leads to a spin structure that
can be viewed as alternatively stacked ferromagnetic and antiferromagnetic
tetrahedra in a three-dimensional checkerboard form. Stable coexistence of
these opposing types of clusters is enabled by the bipartite
breathing-pyrochlore crystal structure, leading to a second order phase
transition at 10 K. The diffraction intensity of ZnFe2O4 is an exact complement
to the inelastic scattering intensity of several chromate spinel systems which
are regarded as model classical spin liquids. Our results challenge this
attribution, and suggest instead of the six-spin ring-mode, spin excitations in
chromate spinels are closely related to the (1, 0, 1/2) type of spin order and
the four-spin ferromagnetic cluster locally at one tetrahedron.
