Antiferromagnetic magnetic transition and spin fluctuations in the deformed pyrochlore compoundβ-Fe2(OH)3Cl

Abstract

Magnetism of the rhombohedral structure ${\text{Fe}}_{2}{(\text{OH})}_{3}\text{Cl}$ $[\ensuremath{\beta}{\text{-Fe}}_{2}{(\text{OH})}_{3}\text{Cl}]$, a member of the geometric frustration series ${M}_{2}{(\text{OH})}_{3}X$ where the magnetic ions form a deformed pyrochlore lattice, was studied using dc and ac susceptibilities, heat-capacity, neutron powder-diffraction, and muon spin relaxation $(\ensuremath{\mu}\text{SR})$ measurements. Antiferromagnetic transition was observed at ${T}_{\text{N}}=9.0\text{ }\text{K}$ with a much larger Curie-Weiss temperature ${\ensuremath{\theta}}_{\text{w}}$ of approximately $\ensuremath{-}64\text{ }\text{K}$, suggesting that ${\text{Fe}}_{2}{(\text{OH})}_{3}\text{Cl}$ is a geometrically frustrated magnet. Neutron-diffraction studies revealed the transition into a long-range antiferromagnetic order below ${T}_{\text{N}}=9.0\text{ }\text{K}$ with the ${\text{Fe}}^{2+}$ spins on the triangular lattice planes disordered, and the other ones on the kagome lattice planes having frozen moments of less than 70% of the full ${\text{Fe}}^{2+}$ moment. Spin fluctuations below ${T}_{\text{N}}$ were verified further using $\ensuremath{\mu}\text{SR}$ studies. The magnetically phase-separated feature and the spin fluctuation coexisting with a long-range magnetic order are considered to be of great interest for studying geometric frustration and the behavior of $S=2$ spin systems on prochlore and kagome lattices.