Spin waves and temperature-dependent behaviour of the quasi-two-dimensional antiferromagnet KFeF₄

Abstract

A study of the quasi-twodimensional antiferronmget KFeF4 below the a s i t i o n temperature. TN = 13 K, has been undemken using neutron scattering techniques. The dispersion relation of the spin excitations is well described by a model Hamiltonian incorporating Heisenberg exchange interactions and uniaxial anisotropy. The anisotropy controls the energy of the zone centre mode whose frequency varies in the same way with temperature as the square of the staggered magnetization which is described by the two-dimensional king model. Dipoledipolecontributions are too small to account fnlly for the anisotropy. Different nearest-neighbour exchange enersies are found along the a and b directions due to different superexchange paths, with Jl = -2.18 meV along a, and Jz = -2.73 meV along b.

Zero-energy excitation in the classical kagome antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$

“…The observed anisotropy gap of 0.21 meV is 25% smaller than the calculated one of 0.28 meV. This reduction is consistent with other systems in which the anisotropy gap in the spin-wave excitation closes upon approaching the transition temperature [27][28][29]. The temperature dependence of the gap in antiferromagnets is known to be roughly proportional to the sublattice magnetization.…”

Spin waves and the critical behaviour of the magnetization in

“…A variation of the spin wave gap with the squared magnetization is less common in low dimensions, although this effect has been seen in another 2D S = 5/2 system, KFeF 4 (Fulton et al 1994). At this point there appears to be no theory to explain this.…”

Quantum Heisenberg antiferromagnets: a survey of the activity in Florence (Review)

“…FIG. 11: The function y(t) = t ln ξ vs t, for (from the rightmost curve) S = ∞, 5/2, 1 and 1/2; the up-triangles 71 and the diamonds 72 are quantum MC data for S = 1/2; also reported are neutron scattering data for La2NiO4 (open circles 54 ), for K2NiF4 (squares 52,53 ), KFeF4 (filled circles 56 ) and Rb2MnF4 (down-triangles 55 ). The abrupt rising of the experimental data for the S = 5/2 compounds at t ≃ 0.65 is due to the effect of the small, but finite, anisotropies and will be discussed in more details in Section V. made in Fig.…”