Partially Disordered Phase in Frustrated Triangular Lattice Antiferromagnet CuFeO₂

Abstract

We reinvestigated successive magnetic phase transitions (T N1 ∼ 14.0 K, T N2 ∼ 10.5 K) in a frustrated triangular lattice antiferromagnet (TLA) CuFeO 2 by neutron diffraction measurements using single crystals. The magnetic structure of the intermediate-temperature phase between T N1 and T N2 is found to be a quasi-long range ordered sinusoidally amplitude-modulated structure with a temperature dependent propagation wave vector (q q 0). These features of successive phase transitions are well explained by reinvestigated Monte-Carlo simulation of a 2D Ising TLA with competing exchange interactions up to 3rd neighbors, in spite of the Heisenberg spin character of orbital singlet Fe 3+ magnetic ions.

Effect of Spin Dilution on the Magnetic State of Delafossite CuFeO2 with an S = 5/2 Antiferromagnetic Triangular Sublattice

“…While Curie-Weiss analysis shows that the dominant long-range interactions in CuFe 1−x Sc x O 2 are antiferromagnetic, the scaled Curie plot reveals the presence of short-range uncompensated behavior in all of the Sc-substituted samples which is likely a result of chemical disorder, which is in a good agreement with results reported by N. Terada et al [31]. The spin dynamics of the geometrically frustrated triangular antiferromagnet multiferroic CuFeO 2 has been mapped out using inelastic neutron scattering [30]. They determined the relevant spin Hamiltonian parameters, showing that the sinusoidal model with a strong planar anisotropy correctly describes the spin dynamics.…”

“…7) which is close to 5.0 meV for the mother CuFeO 2 [30]. The Sc substitution (S = 0) at the Fe sites (S = 5/2) tend to suppress the low ferromagnetic interactions in the magnetic structure J 1 (1) and J 1 (2) [32]; however, the magnetic exchange coupling J BB decreases under 5.0 meV with increasing x.…”

“…The temperature of the χ maximum corresponds to T N1 = 14.5 K, and the second transition, corresponding to an abrupt decrease of the magnetic susceptibility, at 9.1 K for CuFeO 2 , can be associated to T N2 . The latter has to be compared to the value found for the undoped compound [30] (=10.5 K), whereas T N1 is found to be rather independent on x. The Sc for Fe substitution in CuFe 1−x Sc x O 2 makes T N2 decreasing, but T N1 remains almost unchanged.…”

High magnetic field behaviour of the triangular lattice antiferromagnet, CuFeO2

“…It is worth noting, that at T = 10.5 K, both commensurate and incommensurate peaks are present in the diffraction pattern. These results are in general agreement with the previous findings of Mitsuda et al 7 .…”

“…Mitsuda et al have also detected a significant increase of the (110) peak intensity and have attributed this to a dramatic variation of the crystal mosaic, based on the fact that (110) is not present in the neutron powder data 7 . We note that the observed change in width of the (110) peak is only 7% and that the other possible explanations of this effect could be either multiple scattering involving magnetic peaks or a truly magnetic nature of the (100) peak.…”