Magnon dispersion and thermodynamics inCsNiF3

Abstract

We present an accurate transfer matrix renormalization group calculation of the thermodynamics in a quantum spin-1 planar ferromagnetic chain. We also calculate the field dependence of the magnon gap and confirm the accuracy of the magnon dispersion derived earlier through a 1/n expansion. We are thus able to examine the validity of a number of previous calculations and further analyze a wide range of experiments on CsNiF 3 concerning the magnon dispersion, magnetization, susceptibility, and specific heat. Although it is not possible to account for all data with a single set of parameters, the overall qualitative agreement is good and the remaining discrepancies may reflect a departure from ideal quasi-one-dimensional model behavior. Finally, we present some indirect evidence to the effect that the popular interpretation of the excess specific heat in terms of sine-Gordon solitons may not be appropriate.

Magnetic Exchange Interactions and Estimation of TNin CsNiF3from First Principles

“…The negative resulting J indicates the antiferromagnetic, whereas the positive J, the ferromagnetic coupling. The ferromagnetic exchange interaction along the Niatom chain is in excellent agreement with the experimental value of 23.6 K [7,10], but for the antiferromagnetic coupling between Ni-chains the calculated value is about twice the experimental one J = −0.05 K [10]. However, such small exchange interactions are near to the edge of accuracy of total energy calculations.…”

“…The exact estimation of T N within the Heisenberg model would be possible using the time and resources more demanding Monte Carlo approach and it would most likely increase the RPA estimate. The remaining disagreement with respect to the experiment can be probably explained by the presence of crystal field effect, that is of the same order of magnitude compared to the strongest exchange interaction J [7]. Crystal field effects typically decrease estimated critical temperatures [14].…”

“…Such 3D insulating systems occurring at very low temperatures could be very well studied using state-of-art ab initio methods. As the starting point we investigated the strength of the exchange interaction and compared them to the recently revised experimental studies [7,10]. Moreover, the critical temperature (Néel temperature) was calculated using the mean-field theory and random phase approximation.…”

“…Within this plane the onset of antiferromagnetism appears. Many experimental studies have investigated (503) different magnetic properties, for review see [3,4], ultrasonic study of magnetic phases [5], spin waves [6], magnon dispersions [7], excitation spectrum in the magnetic field within [8] and perpendicular [9] to the easy plane and etc. Such 3D insulating systems occurring at very low temperatures could be very well studied using state-of-art ab initio methods.…”

Dynamical Structure Factors of Quasi-One-Dimensional Magnets of the Type of CsNiF3

“…The equations of motion for the spins, i ∂S [7]. Only the nearest-neighbor interactions have been taken into account, 2J RR = J(δ R ,R+1 + δ R ,R−1 ).…”