Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca${}_3$CoNb${}_2$O${}_9$

Abstract

We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca${}_3$CoNb${}_2$O${}_9$, in which the effective spin of Co${}^{2+}$ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant $\hat{I}{¸}_{CW}\sim$ $-55$ K and the low Neel temperature($T_N\sim$ 1.45 K) give a frustration factor $f$ ($=\mid \hat{I}{¸}_{CW}/T_N\mid$) $\approx$ 38, suggesting that Ca${}_3$CoNb${}_2$O${}_9$ resides in strong frustration regime. Slightly below $T_N$, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization $M_s$ is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca${}_3$CoNb${}_2$O${}_9$ is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy.