High-Pressure-Stabilized Post-Spinel Phase of CdFe 2 O 4 with Distinct Magnetism from Its Ambient-Pressure Spinel Phase.

α-CdFe 2 O 4 stabilizes its normal spinel structure due to the covalent Cd-O bond, in which all the connections between adjacent FeO 6 octahedral are edge-shared, forming a typical geometrically frustrated Fe 3+ magnetic lattice. As the high-pressure methods were utilized, the post-spinel phase β-CdFe 2 O 4 with a CaFe 2 O 4 -type structure was synthesized at 8 GPa and 1373 K. The new polymorph has an orthorhombic structure with the space group Pnma and an 11.5% higher density than that of its normal spinel polymorph (α-CdFe 2 O 4 ) synthesized at ambient conditions. The edge-shared FeO 6 octahedra form zigzag S = 5/2 spin ladders along the b -axis dominating its low-dimensional magnetic properties at high temperatures and a long-range antiferromagnetic ordering with a high Néel temperature of T N1 = 350 K. Further, the rearrangement of magnetic ordering was found to occur around T N2 = 265 K, below which the competition of two phases or several couplings induce complex antiferromagnetic behaviors.