Absence of magnetic long range order in Y2CrSbO7: bond-disorder induced magnetic frustration in a ferromagnetic pyrochlore

The consequences of random nonmagnetic-ion dilution for the pyrochlore family Y2(M1−xNx )2O7 (M = magnetic ion, N = nonmagnetic ion) have been investigated. As a first step, we experimentally examine the magnetic properties of Y2CrSbO7 (x = 0.5), in which the magnetic sites (Cr3+) are percolative. Although the effective Cr-Cr spin exchange is ferromagnetic, as evidenced by a positive Curie-Weiss temperature, CW 19.5 K, our high-resolution neutron powder diffraction measurements detect no sign of magnetic long-range order down to 2 K. In order to understand our observations, we construct a lattice model to numerically study the bond disorder introduced by the ionic size mismatch between M and N, which reveals that the bond disorder percolates at xb 0.23, explaining the absence of magnetic long-range order. This model could be applied to a series of frustrated magnets with a pyrochlore sublattice, for example, the spinel compound Zn(Cr1−xGax )2O4, wherein a Néel to spin glass phase transition occurs between x = 0.2 and 0.25 [Lee et al., Phys. Rev. B 77, 014405 (2008)]. Our study stresses the non-negligible role of bond disorder on magnetic frustration, even in ferromagnets. D