Deuterium freedom and M–I transition in (DMe-DCNQI)2Cu system

Abstract We have discovered that orientation freedom in a deuterated methyl group introduces two kinds of anomalous specific heat on the deuterated (DMe-DCNQI) 2 Cu system. In systems containing methyl groups with one deuterium atom (CH 2 D), we find the Schottky type of specific heat. In systems with CHD 2 , we observe peaks not of the Schottky type. To find out the origin and mechanism of these anomalies, we carried out the thermal study on the mixed crystals. We clarified the possibility of the order–disorder transition of CHD 2 orientation along the c -axis.