Intra-chain superexchange couplings in quasi-1D 3d transition-metal magnetic compounds

Ferromagnetic Half-Metal Cyanamides Cr(NCN)2 Predicted from First Principles Investigation

The stability, physical properties, and electronic structures of Cr(NCN)₂ were studied using density functional theory with explicit electronic correlation (GGA+U). The calculated results indicate that Cr(NCN)₂ is a ferromagnetic and half-metal, both thermodynamically and elastically stable. A comparative study on the electronic structures of Cr(NCN)₂ and CrO₂ shows that the Cr atoms in both compounds are in one crystallographically equivalent site, with an ideal 4+ valence state. In CrO₂, the Cr atoms at the corner and center sites have different magnetic moments and orbital occupancies, moreover, there is a large difference between the intra- (12.1 meV) and inter-chain (31.2 meV) magnetic couplings, which is significantly weakened by C atoms in Cr(NCN)₂.

Short-Range Antiferromagnetic Ordering of Netlike S = 1/2 Linear Trimeric Units in the Copper Germanate K2Cu3Ge4O12

K₂Cu₃Ge₄O₁₂ was synthesized via a solid-state reaction in a high-temperature experiment at 1073 K. Crystal structure analysis provided the following data: space group Cmcm (no. 63), a = 1407.9(2), b = 578.0(1), c = 1389.2(1) pm, V = 1.1305 nm³, and Z = 4. The structure consists of alternating layers of netlike arranged trimeric [Cu₃O₈]^10- units and layers of four-membered rings of GeO₄ tetrahedra. The potassium cations connect the different structural moieties. Although both structural motifs are well-known, the way they are connected in K₂Cu₃Ge₄O₁₂ is unique. K₂Cu₃Ge₄O₁₂ was further characterized via vibrational spectroscopy and SEM-EDX measurements. Magnetic measurements exhibit an antiferromagnetic behavior at low temperatures along with an unusual pseudo-2D coupling.