J. Phys. I France
Volume 6, Numéro 12, December 1996
Page(s) 1987 - 1996
DOI: 10.1051/jp1:1996194
J. Phys. I France 6 (1996) 1987-1996

Magnetic Properties of Coexistent System of Itinerant and Localized Electrons, (BEDT-TTF) $\mathsf{_2}$MCo(SCN) $\mathsf{_4}$ (M = K, Rb, Cs)

Hatsumi Mori1, Shoji Tanaka1 and Takehiko Mori2

1  International Superconductivity Technology Center, Shinonome, Tokyo 135, Japan
2  Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152, Japan

(Received 30 April 1996, revised 8 July 1996, accepted 19 August 1996)

A coexistent system of itinerant and localized electrons was prepared and the magnetic properties of both electrons were investigated. $\alpha$-(BEDT-TTF) 2CsCo(SCN) 4 (abbreviated as the CsCo salt), $\alpha$-(BEDT-TTF) 2RbCo(SCN) 4 (the RbCo salt), and $\alpha''$-(BEDT-TTF) 2K 1.4Co(SCN) 4 (the KCo salt), undergo metal-insulator transitions at 20 K. 190 K, and 130 K, respectively. The ESR measurement of the RbCo salt indicates that the electronic state below transition temperature, 190 K, is magnetic insulator due to the strong electron correlation. The static magnetic susceptibility of the CsCo salt measured by SQUID is mostly originated from the localized electrons, Co $^{2+}\,(S=3/2)$, and obeys the Curie-Weiss law with $\theta = -3$ K above 20 K, where the weak interaction between Co 2+ might be caused by the superexchange through coordinated SCN - anion. below 20 K, the rapid decrease of $\chi T$ is observed because of the crystal field around Co 2+.

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