The compound {Ho(-fur)3}n, where -fur represents the -furoate ligand (C4H3OCOO−), forms one-dimensional zigzag chains with Ho(III) ions bridged by furoate ligands. These chains run along the crystallographic c-axis. Due to positional disorder of one furoate ligand, two slightly distinct coordination environments, denoted Ho(A) and Ho(B), arise. Ab initio calculations were performed to estimate the zero-field splittings for both Ho sites.
Magnetic susceptibility and heat capacity measurements show that at low temperatures, the compound behaves as an assembly of antiferromagnetically coupled S = 1/2 Ising-like chains (J/kB ≈ −0.4 K) of Ho ions with transverse anisotropy. Low-temperature susceptibility further reveals a small concentration of chain defects. Zero-field ac susceptibility measurements evidence slow relaxation of the magnetization assigned to defect-enabled single-chain magnet (SCM) dynamics in the two chain types, with activation energies EA,SCM = 2.9(3) K and EB,SCM = 4(3) K.
Below 0.4 K, a crossover to a coherent quantum tunneling of the magnetization regime, assisted by hyperfine interactions, is observed. The relaxation behavior is discussed in comparison with related compounds {Ln(-fur)3}n (Ln = Dy, Tb) and {Ho2Ba(-fur)8}n, highlighting the interplay between Kramers versus non-Kramers ion character, hyperfine interactions, and magnetic exchange topology in governing the low-temperature dynamics.
The research, involving Javier Luzón, Silvia Melnic, Sergiu Shova, and Juan Bartolomé, is part of the M4ELC Sustainable Electronics project and has been published in Low Temp. Phys. 52, 1089–1101 (2026) with DOI: 10.1063/10.0044825.
