Low temperature magnetic properties of some new high-pressure perovskite phases of iron II: Observation of novel slow paramagnetic relaxation in CaFe₂Ti₂O₆ and CaFe₃Ti₄O₁₂

Results of iron-57 Moessbauer spectroscopy and ac and dc susceptibility study of the double perovskite phases, CaFeTi₂O₆ (A) and CaFe₃Ti₄O₁₂ (B) are presented. Both phases exhibit spectral broadening effects with decreasing temperature and incipient magnetic hyperfine splitting attributable to novel slow paramagnetic relaxation at the tetrahedral and square planar sites of (A) and the square planar sites of (B). The temperature dependence of magnetic moment for (A) corresponds to classical single ion zero field splitting, while that of (B) indicates antiferromagnetic exchange interactions. There is no evidence of cooperative long range magnetic order in these materials.