Short-range magnetic ordering in the highly frustrated pyrochlore Y2Mn2O7

The bulk magnetic susceptibility of Y2Mn2O7 is suggestive of ferromagnetic order, with FTHETAC=+41(2) K, and an apparent Tc=20 K. However, both dc and ac susceptibility data show a broad maximum near 7 K, which is frequency and field dependent. Heat-capacity studies down to 2 K show no evidence for long-range magnetic order. Neutron-scattering data indicate the presence of both antiferromagnetic (first neighbors) and ferromagnetic (second and third neighbors) short-range correlations. These results are compared to mean-field-theory predictions for the highly frustrated 16c sites in the pyrochlore lattice. This material shows many properties in common with spin glasses in spite of the fact that there is no evidence for chemical disorder.