Millimetre-wave ESR (electron-spin resonance) measurements of frustrated system ZnCr2xGa2–2xO4

The magnetic properties of a three-dimensional topological frustrated system ZnCr2xGa2-2xO4, which is an anti-ferromagnet with a spinel structure, have been investigated by our millimetre-wave ESR (electron-spin resonance) measurements using the pulsed magnetic field up to 16 T in the temperature region from 1.8 to 265 K. In the high-temperature region, typical Cr3+ EPR (electron-paramagnetic resonance) with the g-value of 1.95 was observed. For the x=1 sample, AFMR (anti-ferromagnetic resonance) with the easy-plane-type magnetic anisotropy was observed below TN. It turned out that the anti-ferromagnetic gap opens up just below TN suggesting that the transition is of the first order. The x dependences of ESR were also observed and their temperature dependences of the g-value and the linewidth will be discussed in connection with those of other frustrated systems such as Kagome lattice substance.