Soliton-Mediated Magnetic Phase Transition in the Frustrated Antiferromagnet CsCoCl₃

Abstract

Hexagonal CsCoCl₃ is a quasi-one-dimensional (1D) S=1/2 Ising antiferromagnet with intrachain interaction J=-75K. With decreasing temperature, a 3D magnetic transition occurs due to the weak antiferromagnetic interchain interaction as usual. However, a frustration effect due to triangular arrangement of the constituent magnetic chains in the c-plane gives rise to unusual successive phase transitions at T_N1=21K and T_N2=9K. The spin frustration model identifies the intermediate-temperature phase between T_N1 and T_N2 as a partially disordered (PD) phase in which 2/3 of magnetic chains order antiferromagnetically with each other, leaving the rest uncorrelated, and the low-temperature phase below T_N2 as a ferrimagnetic (FR) phase in which all magnetic chains order in a collinear ferrimagnetic arrangement. While the model has succeeded in explaining the various experimental results, there remain several basic questions; Whether the PD phase is stable or not? How can 1/3 of chains behave paramagnetically? What happens at T_N2? We have carried out magnetic resonance experiments (NMR, ESR) in order to solve these problems from a microscopic point of view.