Cluster Spin Glass Formation in the Double Double Perovskite CaMnFeTaO<sub>6</sub>
Padraig S. Kearins, Elena Solana‐Madruga, Kunlang Ji, C. Ritter, J. Paul Attfield
Abstract
CaMnFeTaO6 has been synthesized at 1200 °C under 10 GPa pressure. Powder neutron diffraction shows that CaMnFeTaO6 adopts a double double perovskite structure (tetragonal space group P42/n, lattice parameters a = 7.683(3) and c = 7.685(7) Å) with cation disorder at all transition-metal sites. Magnetization measurements reveal an apparent ferro- or ferrimagnetic transition at Tm1 = 51 K and a susceptibility peak at Tm2 = 20 K, but no long-range magnetic order is observed by neutron diffraction down to 1.5 K. This is attributed to the formation of superparamagnetic clusters of ferrimagnetically ordered spins below Tm1 that freeze into a cluster spin glass at Tf = Tm2. ac magnetization measurements confirm the cluster spin glass ground state. Disorder from the substitution of Fe2+ for Mn2+ and Fe3+/Ta5+ inversion disrupts the network of superexchange interactions leading to the cluster spin glass ground state, in contrast to other P42/n double double perovskites where long-range magnetic order is stabilized.