Results of pulsed field antiferromagnetic resonance (AFMR) experiments are briefly summarized for themixed crystal system(Cr2O3)1−x·(Al2O3)xas a function of temperature, andX, whereX = 0.003, 0.006,0.008, 0.06, 0.1, 0.2, and 0.9. The temperature dependence of the critical field,(2&lgr;K)12, for pureCr2O3andX = 0.1are compared in detail. The increase of(2&lgr;K)12at 4.2°K from about 59 kilogauss forCr2O3to 79kilogauss forX = 0.1is attributed to a reversal in sign and rapid increase in magnitude of the effectivecrystalline field contribution to the anisotropy energy asXis increased. AFMR linewidths from 800 to2000 gauss were observed, but forX≤0.2the linewidth was almost independent of temperature for eachcomposition. The decrease of Ne´el temperature with increase ofXis also summarized.