Partially disordered phase in frustrated triangular lattice antiferromagnet CuFeO2

We reinvestigated successive magnetic phase transitions (TN1 similar to 14. 0 K, TN2 similar to 10.5 K) in a frustrated triangular lattice antiferromag net (TLA) CuFeO2 by neutron diffraction measurements using single crystals. The magnetic structure of the intermediate temperature phase between TN1 a nd TN1 is found to be a quasi-long range ordered sinusoidally amplitude-mod ulated structure with a temperature dependent propagation wave vector (q q 0). These features of successive phase transitions are well explained by re investigated Monte-Carlo simulation of a 2D Ising TLA with competing exchan ge interactions up to 3rd neighbors, in spite of the Heisenberg spin charac ter of orbital singlet Fe3+ magnetic ions.