Switching of dominant magnetic exchange interactions between tetrahedral–octahedral and octahedral–octahedral sites in (Mn_1−xCr_x)₃O₄ spinels

Abstract

Magnetic exchange interactions in Mn3O4 spinel systems are complicated due to the presence of magnetic frustration between one tetrahedral and two octahedral sites, and the strongly correlated Jahn-Teller crystal distortion...

Interplay of lattice-spin-orbital coupling and Jahn–Teller effect in noncollinear spinel Ti x Mn1−x (Fe y Co1−y )2O4: a neutron diffraction study

“…Low-temperature x-ray powder diffraction studies of M8F4 provide evidence for the tetragonal distortion from the cubic structure with the space group I4 1 /amd below 258 K which is close to the onset of FiM ordering. At 12 K the characteristic c t /√2a t ratio turns out to be 0.99795 (8). However, the second composition having higher Fe containing (M6F8) acts differently wherein the JT active cations counteracts the pronounced tetragonal distortions although the FiM ordering sets in at much higher T C = 365 K. A coexistence of weak antiferromagnetism and strong ferrimagnetism is clearly evident from the neutron diffraction data in both compounds which is also observed in isostructural spinels plays a significant role on the global magnetic behaviour [23,26].…”

“…Contrary to the cubic setting the ferromagnetic (FM) component is now fixed to be line up collinear to the c axis of tetragonal unit cell. Therefore, the non-collinear AF order seems to be stable in the ab plane, where the spins orient along the directions [110] and [1][2][3][4][5][6][7][8][9][10], respectively. The Fourier coefficients S k (j) of octahedral atoms under the cubic and tetragonal symmetries being S k (B3,c) = (u,−u,v), S k (B4,c) = (−u,u,v); and (ii) for tetragonal S k (B1,t) = (0,−u,v), S k (B2,t) = (0,u,v), S k (B3,t) = (u,0,v), S k (B4,t) = (−u,0,v).…”

“…Such exchange interactions with competing order together with the Jahn-Teller-like electron-lattice coupling have been extensively investigated in recent past to illuminate the coexistence of various magnetic phases present in a single system [4][5][6]. Among various families of oxides, spinel systems serve as the model systems to probe various unique magnetic phenomena which can be explained based on the various mechanisms of exchange interactions [7,8]. Normal spinels stabilize their crystal structure in cubic-close packing arrangement of O 2− anions with divalent and trivalent metal cations located at tetrahedral or octahedral sites having the chemical formulae (A 2+ ) tetr [B 3+ 2 ] oct O 4 or (B 2+ ) tetr [A 3+ B 3+ ] oct O 4 .…”