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

TL;DR

This study investigates the magnetic properties of Ca$_3$CoNb$_2$O$_9$, a frustrated triangular lattice antiferromagnet with weak anisotropy, revealing complex magnetic states and significant frustration effects.

Contribution

It provides the first detailed magnetic characterization of Ca$_3$CoNb$_2$O$_9$, highlighting its strong frustration and novel magnetic behavior near the Neel temperature.

Findings

Large frustration factor (~38) indicating strong magnetic frustration.

Observation of deviation between ZFC and FC susceptibility below T_N.

Identification of a magnetic state with 1/3 of saturation magnetization.

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 $\theta_{CW}\sim$ $-55$ K and the low Neel temperature($T_N\sim$ 1.45 K) give a frustration factor $f$ ($=\mid\theta_{CW}/T_N \mid$) $\approx$ 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.