Solid Solutions between BiMnO and BiCrO.

Solid solutions BiMnCrO (0 ≤ x ≤ 1) have been prepared at 6 GPa and 1370-1620 K. Their structural properties have been studied with synchrotron X-ray powder diffraction, and their physical properties have been investigated by dc/ac magnetic, specific heat, dielectric, and differential scanning calorimetry measurements. A magnetic phase diagram of BiMnCrO is established. A phase with orbital ordering observed in BiMnO is suppressed at x > 0.1, accompanied by a drop in the ferromagnetic Curie temperature T from 101 K for x = 0 to 76 K for x = 0.15 and sharp changes in the lattice parameters. The T value monotonically decreases up to x = 0.3 (with T = 53 K). For intermediate compositions with x = 0.4, 0.5, spin-glass magnetic properties are found at 28 and 24 K, respectively. The Néel temperature T linearly increases from 36 K for x = 0.6 to 111 K for x = 1.0. A spin-reorientation transition is observed at 61 K for x = 0.9 and 72 K for x = 1.0. Re-entrant spin-glass transitions are also observed for samples with x = 0.3, 0.6, 0.7 by ac susceptibility at low temperatures. At high temperatures, a structural phase transition from C2/c to Pnma symmetry is observed for all compositions with a monotonic change of the phase transition temperature. The magnetic phase diagram from the BiMnO-rich side (x ≤ 0.5) resembles a phase diagram of BiMnScO solid solutions, indicating that the nature of substituting cations (magnetic or nonmagnetic) is not crucial for doped BiMnO.