Origin of low-temperature deviations in Fe(III) chain susceptibility

Determine whether the deviations in the low-temperature magnetic susceptibility of the largest investigated open Fe(III) spin chains arise from insufficient convergence of thermal DMRG using Time Evolution Block Decimation or from impurities in real materials that produce a distribution of chain lengths.

Background

The paper studies open chains of iron(III) ions with spin quantum number si=5/2s_i=5/2 and nearest-neighbor exchange interactions. Thermal DMRG can treat chain lengths beyond the range accessible to the finite-temperature Lanczos method, and the calculated low-temperature susceptibility develops an upturn that approaches the experimental behavior as the chain length increases.

Despite this apparent agreement, the susceptibility curves for the largest chains still show low-temperature deviations. The paper does not resolve whether these discrepancies are numerical artifacts caused by insufficient bond dimension or convergence in the thermal DMRG-TEBD calculations, or instead reflect the fact that experimental spin chains are interrupted by impurities and therefore have a distribution of finite chain lengths.

References

It remains, however, open whether the deviations of the low-temperature behavior between the largest investigated chains are due to still insufficient convergence of thDMRG-TEBD or due to the experimental observation that spin chains in real materials are interrupted by impurities and thus constitute a distribution of various chain lengths.

— Thermal DMRG for quasi one-dimensional magnetic molecules and chains  (2608.24608 - Horstmann et al., 25 Aug 2026) in Section 3.3, “Fe(III) chains and rings”