We have utilized a novel technique to measure both the magnetization and magnetoresistance of a single crystal of ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$Cl${\mathrm{O}}_4$ in the regime where the magnetic field induces a series of metal-to-semimetal transitions. We find anisotropic magnetization with extremely sharp oscillatory structure similar to that expected for a quantized two-dimensional electron gas. However, the temperature and field dependences of the anomalies suggest a series of first-order phase transitions as opposed to the conventional de Haas-van Alphen effect. The entropy loss is comparable to the entropy of the electron gas.

• Received 23 April 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.969