Re-entrant spin-glass behavior in the frustrated pyrochlore Y2Mn2O7 (abstract)

Materials with the pyrochlore structure are subject to extreme frustration due to the topology of the magnetic sublattice which consists of a three-dimensional array of perfect corner sharing tetrahedra. The pyrochlore Y2Mn2O7 has been studied recently.1 The compound is crystalline and appears to have negligible crystallographic disorder, yet its magnetic properties resemble those of a re-entrant spin glass with a ferromagetic-like anomaly in the susceptibility at 17 K followed by a maximum at 7 K. In order to characterize this behavior dc and ac susceptibility measurements have been carried out along with small angle neutron scattering (SANS). Analysis of the spin dynamics through the frequency and temperature dependence of χ′ and χ″ show evidence for spin-freezing below 4 K. The SANS data can be fit by a cross section with both Lorentzian (L) and Lorentzian-squared (L2) terms. Both the magnitude and temperature dependence of the correlation lengths, ξ, of the L and L2 terms are different with ξ(L) growing to a finite size ∼25 Å at 15 K but ξ(L2) becomes resolution limited at the same temperature. In many respects the behavior of Y2Mn2O7 parallels that seen in magnetic metallic glasses.2