Susceptibilities of the vanadium Magneli phases V/sub n/O/sub 2n/-1 at low temperature

The magnetic susceptibilities of the insulating Magneli phases V3O5, V4O7, V6O11, and V8O15 have been measured at low temperatures. Due to a short-range-order effect V3O5 exhibits a broad maximum at 125 K, which is substantially higher than the Neel temperature, 76 K, of this compound. For V4O7 and V6O11 the difference between the Neel temperature and the temperature of the maximum in the susceptibility is small. This excludes the possibility that a linear-chain model discussed by Khattak et al. can explain the specific heat of these two compounds. The temperature derivative of the susceptibility for these two compounds has a maximum at the Neel temperature which corresponds to Fisher's relation. The susceptibility for V8O15 is nearly constant between 5.6 and 68 K, and depends on past history below 5.6 K i.e., whether the sample is being cooled or heated. However this temperature hysteresis is sample dependent. These experimental data can not be accounted for by an ordinary antiferromagnetic transition in the insulating state and suggest another type of transition. The possibility of the existence of a mixed charge-density and spin-density wave is discussed, since this can explain qualitatively the experimental features found for V8O15