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

Magnetism of the rhombohedral structure Fe-2(OH)(3)Cl [beta-Fe-2(OH)(3)Cl], a member of the geometric frustration series M-2(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 (mu SR) measurements. Antiferromagnetic transition was observed at T-N=9.0 K with a much larger Curie-Weiss temperature theta(w) of approximately -64 K, suggesting that Fe-2(OH)(3)Cl is a geometrically frustrated magnet. Neutron-diffraction studies revealed the transition into a long-range antiferromagnetic order below T-N=9.0 K with the Fe2+ 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 Fe2+ moment. Spin fluctuations below T-N were verified further using mu 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.