Influence of topological frustration on the magnetic properties of the normal oxyspinel CdFe2O4

Study of the Influence of Electron Spin in Ferromagnetism and Thermoelectric Characteristics of CdTm2Y4 (Y = S, Se) Spinels for Spintronic Applications

The current study used full-potential methods to examine the ferromagnetic characteristics of CdTm2Y4(Y= S, Se) spinels; i.e., structural, elastic, electronic, and thermoelectric characteristics of these spinels have been explored for the first time. We used PBEsol-GGA for enthalpy of formation calculations to explain the stability of the ferromagnetic state and calculate the elastic constants and corresponding mechanical modules to reveal the ductile behavior of the materials. The mBJ potential is used instead of PBEsol-GGA to obtain more accurate and precise results of electronic and thermoelectric characteristics. Using mBJ potential leads to complete occupation of the bands in the materials and a clear interpretation of the density of states (DOS). The analysis of the electronic band structure and DOS reveals the stability of the ferromagnetic state in the analyzed materials as a result of p-d hybridization-based exchange splitting of Tm cations in the lattice. The calculations of thermoelectric efficiency are effective in evaluating the aptitude pertinence of the material in waste energy recovery systems and other technological applications. The thermal parameters of these materials are also analyzed to examine their thermal stability over a wide range of temperatures. The results of these calculations are essential for determining the suitability of the materials for use in spintronics-based devices and thermoelectric appliances as these devices rely heavily on the material's thermoelectric properties.

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

α-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 β-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 (α-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 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.

Quantum tetrahedral mean field theory of the magnetic susceptibility for the pyrochlore lattice

A quantum mean field theory of the pyrochlore lattice is presented. The starting point is not the individual magnetic ions, as in the usual Curie-Weiss mean field theory, but a set of interacting corner-sharing tetrahedra. We check the consistency of the model against magnetic susceptibility data and find good agreement between the theoretical predictions and the experimental data. Implications of the model and future extensions are also discussed.