$\textit{Ab initio}$ description of magnetic properties of spin-glass pyrochlore NaSrMn$_{2}$F$_{7}$

TL;DR

This paper uses first-principles calculations and Monte Carlo simulations to analyze the magnetic properties of NaSrMn$_{2}$F$_{7}$, revealing its spin-glass behavior and identifying the dominant exchange interactions.

Contribution

It introduces a DFT+$U$+SOC approach to derive the spin Hamiltonian and demonstrates that magnetic behavior is primarily governed by nearest neighbor Heisenberg exchange in this complex material.

Findings

No phase transition observed in simulations.

Magnetic properties dominated by nearest neighbor exchange.

Phase transition temperature estimated at 2.6 K.

Abstract

In this study, I have investigated the magnetic and critical properties of manganese pyrochlore fluoride NaSrMn$_{2}$F$_{7}$, which exhibits a glass transition at T$_\text{f}$$=$2.5 (K) due to charge disorder. A DFT+$U$+SOC framework is used in this paper to derive spin-Hamiltonian terms, including isotropic and anisotropic exchange interactions. An optimized geometry reveals a local distortion of the F-Mn-F angle along the $ < $111$ > $ direction (95.48$^{\circ}$ and 84.51$^{\circ}$), which is considered a weak bond disorder ($\delta J$). In spite of the complex structure of this material, first principle calculations show that its magnetic properties are only controlled by the nearest neighbor's Heisenberg exchange interaction, and other interactions do not affect spin arrangements in the ground state. Thus, this material is considered a suitable candidate for studying electron correlation in spin glasses. Using a replica-exchange framework, Monte Carlo simulations indicate that no phase transition is observed when magnetic susceptibility changes with temperature. Based on $\delta J$ and the spin Hamiltonian, 2.6 (K) is obtained as the phase transition temperature.