  Bilayered Sr3Ru2O7 is an unusual metamagnetic metal with inherently
antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial
substitution of Ru by Mn results in the establishment of metal-insulator
transition (MIT) at TMIT and AFM ordering at TM in Sr3(Ru1-xMnx)2O7. Using
elastic neutron scattering we determined the effect of Mn doping on the
magnetic structure and in-plane magnetic correlation lengths in
Sr3(Ru1-xMnx)2O7 (x = 0.06 and 0.12). With increasing Mn doping (x) from 0.06
to 0.12 or decreasing temperatures for x=0.12, an evolution from an in-plane
short-range to long-range double-stripe AFM ground state occurs. For both
compounds, the onset of magnetic correlation with an anisotropic behavior
coincides with the sharp rise of the electrical resistivity and the specific
heat. Since it does not induce measurable lattice distortion, the double-stripe
magnetic order with anisotropic spin texture breaks the symmetry from C4v
crystal lattice to C2v magnetic sublattice. These observations shed new light
on an age-old question of Slater versus Mott-type MIT.
