Anisotropic spin dynamics in the frustrated chain Ca3Co2O6 detected by single-crystal Co-59 NMR

作者：Shimizu Yasuhiro^*; Horibe Munehisa; Nanba Hiroshi; Takami Tsuyoshi; Itoh Masayuki

来源：Physical Review B, 2010, 82(9): 094430.

DOI：10.1103/PhysRevB.82.094430

Static and dynamic magnetic properties are investigated by Co-59 NMR measurements on a single crystal of Ca3Co2O6, a rare model of the ferromagnetic Ising chain coupled antiferromagnetically on a triangular lattice. Above a ferrimagnetic order transition temperature T-N=25 K, the static spin susceptibility probed by the Co-59 Knight shift shows anisotropic behavior in the temperature dependence, consistent with ferromagnetic interactions along the c-axis chain and antiferromagnetic interactions in the ab plane. Correspondingly, the dynamical spin susceptibility obtained from the Co-59 nuclear spin-lattice relaxation rate is also highly anisotropic. The intrachain ferromagnetic correlation steeply develops below 300 K while the interchain antiferromagnetic one does below 120 K with the critical exponent expected in the two-dimensional Ising antiferromagnet. Below T-N, the low-energy excitation arising from the predominant spin-wave magnons has an anisotropic full gap, reflecting the strongly Ising nature. Clear microscopic evidence of the ferrimagnetic order is demonstrated in the Co-59 NMR spectra at 5 K. Rotation of the external magnetic field from the ab plane to the c axis shows the first-order transition from the ferrimagnetic to the fully polarized state. The ferrimagnetic state with the uniform magnitude of magnetic moment is observed even in the transverse field adjusted parallel to the ab plane.

• 出版日期2010-9-17