Low temperature specific heat of (V/sub 1-x/Cr/sub x/)2O3 and (V/sub 1-x/Al/sub x/)2O3

In order to provide an independent determination of the hyperfine splitting of the vanadium nucleus in the antiferromagnetic insulating state, the nuclear specific heats of (V/sub 1-x/Cr/sub x/)O3 and (V/sub 1-x/Al/sub x/)2O3 with 0.012 less than or equal to x less than or equal to 0.085 were measured below 10K. The average hyperfine field value of 188.6 kOe is in better agreement with NMR results on V2O3 than previous heat-capacity measurements. For x < 0.04, the specific heat, after subtracting the nuclear contribution, is described by a Debye lattice specific heat proprortional T3. However for x > 0.04, this nonnuclear specific heat for the as grown specimens consists not only of a cubic temperature-dependent contribution but also of an anomalous contribution which is linearly dependent on the temperature. After annealing these specimens, the linear temperature-dependent term completely disappears. This anomalous specific heat shows a striking similarity to that of amorphous materials and may likewise result from localized defects whose density is reduced upon annealing the specimens. The observation of longer thermal relaxation times in these annealed specimens gives further support to the similarity with amorphous materials