arXiv subjects

A. El Mendili

Publications and source records attributed to A. El Mendili.

3 recordsLinked to original sources

arXiv2026

Quantum-classical correspondence for spins at finite temperatures: theory and applications

We derive a rigorous quantum-to-classical mapping for interacting spin systems at finite temperatures. Specifically, the large-$S$ asymptotic form of the partition function is given by the partition function of a classical model for vectors of length $S_C=\sqrt{S(S+1)}$. Quantum corrections to the asymptotic result form a series in powers of $1/[S(S+1)]$. We calculate the leading temperature-independent quantum correction to the magnetic anisotropy constant. The established mapping justifies the use of classical Monte Carlo simulations for realistic magnetic Hamiltonians, including anisotropic and frustrated interactions. As an application, we compute the Curie and Néel temperatures for a range of magnetic materials with known microscopic interaction constants. The obtained transition temperatures are in good agreement with measured values. Monte Carlo results for the magnetic susceptibility of the collinear antiferromagnet MnF$_2$ above and below the transition are also compared with experimental data.

cond-mat.stat-mech↗

arXiv2025

Longitudinal magnons in large-$S$ easy-axis magnets

Longitudinal magnons are a distinct type of multipolar excitations in magnetic materials with large spins $S\ge 1$ and strong easy-axis anisotropy. These excitations have angular momentum $S^z = \pm 2S$ and can be viewed as a propagating full spin reversal. We study longitudinal magnons for the nearest-neighbor Heisenberg ferromagnet and antiferromagnet on a square lattice with large single-ion anisotropy. In the strong-coupling limit, we derive an effective spin-1/2 model including two leading contributions in $J/D$. The effective model provides a simple description of the longitudinal magnon dynamics. For $S=1$, we compare results from several theoretical approaches that include the effective spin-1/2 model, the linked-cluster expansion, the multiboson spin-wave theory, and, for a ferromagnet, an exact two-particle solution. Among these approaches, the multiboson spin-wave theory provides the decay rate of longitudinal magnons and describes evolution of the excitation spectra from strong to weak anisotropy.

cond-mat.str-el↗

arXiv2024

Transverse and longitudinal magnons in strongly anisotropic antiferromagnet FePSe3

FePSe3 is a collinear honeycomb antiferromagnet with an easy-axis anisotropy and large spins S=2. It belongs to a family of magnetic van der Waals materials, which recently attracted a considerable attention. In this work we present an experimental magneto-optical study of the low-energy excitation spectrum in FePSe3, together with its theoretical description. The observed response contains several types of magnon excitations. Two of them are conventional transverse magnons described by a classical theory of antiferromagnetic resonance. Two other modes are identified as multimagnon hexadecapole excitations with an anomalous g factor approximately equal to four times the g factor of a single Fe^2+ ion. These quasiparticles correspond to full reversals of iron spins that coherently propagate in the up-down antiferromagnetic structure. They constitute a novel type of collective excitations in anisotropic magnetic solids, called longitudinal magnons. Comparison between theory and experiment allows us to estimate the microscopic parameters of FePSe3 including exchange coupling constants and the single-ion anisotropy.

cond-mat.str-el↗