Cluster Spin Glass Formation in the Double Double Perovskite CaMnFeTaO₆

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