High-Pressure-Stabilized Post-Spinel Phase of CdFe₂O₄ with Distinct Magnetism from Its Ambient-Pressure Spinel Phase

alpha-CdFe2O4 stabilizes its normal spinel structure due to the covalent Cd-O bond, in which all the connections between adjacent FeO6 octahedral are edge-shared, forming a typical geometrically frustrated Fe3+ magnetic lattice. As the high-pressure methods were utilized, the post-spinel phase beta-CdFe2O4 with a CaFe2O4-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 (alpha-CdFe2O4) synthesized at ambient conditions. The edge-shared FeO6 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 Neel 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.