Colloque CI, Supplement au Journal de Physique III de mars 1997 Jahn-Teller Effect in Copper-Doped Spinel Group

Abstract. Anomalous magnetic properties and various phase transitions observed in some spinels are due to the Jahn-Teller effect. The effect is rather effectively studied in corresponding diamagnetic analogues of such crystals.In the present paper a group of single crystals of normal and converted spinels doped with the two-valent copper Cu2+ has been investigated. In this group of spinels the effect of inversion splitting shows itself classically. The investigations have been done by using radiospectrometers of 10 and 37 GHz frequency in the temperature range 4-300 K.For the first time,in the low-frequency range at the frequency of 10 GHz the full complex of the EPR spectra have been registered which are due to the theory of the inversion splitting.lt consists of five types of the EPR spectra which are due to allowed 3--3+,2--2+, l_-l+ and forbidden 3 _- l +, l +-2-transitions. At passing to a higher frequency of 37 GHz there occurs the frequency transformation of the spectrum,the two EPR spectra are observed which have been observed by many authors in copper complexes in the case of Jahn-Teller effect developing. At present have been developed the general situation of the model of the Jahn-Teller effect.A large quantity of the experiment works has been perfomed. But it is not clear in the explanation and understanding of the appearance of the Jahn-Teller effect in the EPR spectra.lt is necessary to find such an object of the investigations in which the Jahn-Teller effect appears in full. In this paper we study the octahedral copper complex.The ion Cu2+ is situated in the oxygen octahedron. The ground state of th