(Received October 18, 2007)
The thermal average of magnetization of charged spin 1/2 particles is calculated in terms of a pure state. This leads to the introduction of a temperature-dependent Pauli matrix. A new Bogoliubov transformation for a spin system in thermofield dynamics is then proposed. This transformation clarifies the physical significance of the temperature-dependent Pauli matrix. Generalization to the case of arbitrary spin is straightforward.
URL : http://ptp.ipap.jp/link?PTP/118/1157/
DOI : 10.1143/PTP.118.1157