Unusual Magnetic Properties Of The D+Af And M+Af Phases In Cuge1-Xsixo3

The thermal expansion, specific heat and magnetization of CuGe1-xSixO3 have been studied. Although the Neel temperature T-N Of the D + AF phase, where the antiferromagnetic (AF) phase coexists with the dimerized (D) one, is proportional to x up to 0.02 in H = 0 as in Cu1-xZnxGeO3, T-N Of the M + AF phase, where the AF phase coexists with the magnetic (M) one above 10 T, suddenly increases with x between x = 0.005 and 0.008. The AF properties in the D + AF phase are quite unusual in contrast with the normal ones in the AF state for x = 0.02. This is because the AF properties in the D + AF phase are largely influenced by the existence of dimerization as a background, which exists below T-SP, and the quantum effect plays an important role in this phenomenon.