High-field magnetization and ESR studies of spin-chain compound Ca3CoMnO6

We have preformed high-field magnetization and ESR studies of spin-chain compound Ca3CoMnO6. Magnetization measurements reveal two metamagnetic transitions at Hc1=5.7 T and Hc2=20.5 T, respectively. The former is significantly hysteretic and field-sweep-rate dependent, while the latter is non-hysteretic and field-sweep-rate independent. The X-band ESR measurement reveals a resonance of Mn ions superimposed by six hyperfine-structure peaks due to 55Mn nuclei (I=5/2). High-field ESR data exhibit four different resonance modes. A signature of zero-field spin gap is observed and its origin is discussed.