We performed terahertz ESR measurements of spin frustrated spinel compound GeCo

THz electron spin resonance (ESR) measurements of the spinel compound GeCo2O4, which consists of the Co 2+ pyrochlore structure, were performed. The temperature dependence measurements revealed new antiferromagnetic phases, AF1 and AF2, below TN. Moreover, a wide magnetic field range of ESR study using a single crystal at 1.8 K also revealed various field-induced phases due to the competition between the spin-lattice coupling and the spin-frustration. Critical field resonances were observed at 5.

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