Ultrasound measurements in the spinel compound GeCo2O 4

Abstract

Elastic properties of the spinel compound GeCo2O4 were investigated by the ultrasound velocity measurements in the single crystal. Absence of the elastic softening in (C11- C12)/2 in the paramagnetic state suggests the Jahn-Teller inactive character of Co 2+, despite the presence of the orbital degree of freedom. The pronounced C44 anomaly in the paramagnetic state near TN alternatively suggests that the ultrasound dominantly couple to the exchange interactions among Co2+ ions by the exchange striction effect. The present results conclude that Co2+ adopts the high spin state in this substance. In the antiferromagnetic phase, new elastic anomalies were observed only in (C11- C12)/2 implying the occurrence of the magnetic transitions triggered by the exchange interactions within the Co 2+ bonds along [110] directions. © 2007 IOP Publishing Ltd.