Magnetic properties of chromium ions in oxide matrices. Part 1.—Cr2O3-Al2O3 solid solutions

Magnetic susceptibilities (77 to 700 K) and e.p.r. spectra (100 to 573 K ) have been measured for a series of spinel solid solutions MgCrxAl2–xO4 with x varying from 0.002 to 2. The Racah parameter B has been obtained from optical reflectance spectra. All the solutions obey the Curie-Weiss law and the effective magnetic moments lie in the region 3.87 ± 0.05µβ except at x= 1.5 where (below 500 K)µeff= 4.1µβ. Solutions dilute in chromium give e.p.r. spectra characteristic of chromium ions isolated in the spinel lattice (Iµ resonance). At x= 0.2 a broad resonance ϕ replaces the Iµ resonance between x= 0.4 and x= 2. These results, together with the temperature variation of the e.p.r. resonance ϕ, are correlated with the susceptibility and optical measurements. The interpretation of the results is based on the variations in cation-cation interaction with increasing chromium content. The results obtained for the spinel series of solid solutions are compared with those obtained for the corundum series in part 1.