Theoretical analysis of neutron scattering results for quasi-two dimensional ferromagnets

TL;DR

This paper analyzes neutron scattering data for quasi-two-dimensional ferromagnets using a semi-classical model, revealing its limitations and emphasizing the need for a full quantum approach for low-spin systems.

Contribution

It demonstrates the failure of semi-classical models to accurately describe low-spin ferromagnets, highlighting the necessity for quantum formalism in such analyses.

Findings

Semi-classical model produces negative dynamical structure functions.

Model fails to match experimental results for low-spin systems.

Quantum formalism is likely required for accurate analysis.

Abstract

A theoretical study has been carried out to analyse the available results from the inelastic neutron scattering experiment performed on a quasi-two dimensional spin-1/2 ferromagnetic material $K_2CuF_4$. Our formalism is based on a conventional semi-classical like treatment involving a model of an ideal gas of vortices/anti-vortices corresponding to an anisotropic XY Heisenberg ferromagnet on a square lattice. The results for dynamical structure functions for our model corresponding to spin-1/2, show occurrence of negative values in a large range of energy transfer even encompassing the experimental range, when convoluted with a realistic spectral window function. This result indicates failure of the conventional theoretical framework to be applicable to the experimental situation corresponding to low spin systems. A full quantum formalism seems essential for treating such systems.