Co-existence of long-range order and spin fluctuation in a new geometric frustration series M 2(OH) 3Cl

Abstract

Recently, we observed the co-existence of a long-range magnetic order and spin fluctuation in a clean compound of clinoatacamite, Cu 2(OH) 3Cl (PRL95 (2005) 057201). The present work reports magnetic studies on other compounds of this transition metal series M 2(OH) 3Cl, where M represents three-dimensional (3D)-electron magnetic ions of Co 2+, Fe 2+, etc., respectively. The present study shows that this co-existence is a common feature of the M 2Cl(OH) 3 series, no matter whether it is anti-ferromagnetic, as in the case of Fe 2(OH) 3Cl ( T N=15 K), or ferromagnetic, as in the case of Co 2(OH) 3Cl ( T C=10.5 K). These compounds show a 3D network of corner-sharing tetrahedrons for the magnetic ions. The tetrahedron is slightly tilted with roughly 10% longer distance between the M–M bonded by Cl than those bonded by O and this distortion is suspected to be responsible for the partial order. This research suggests that the transition metal hydroxyhalide M 2Cl(OH) 3 series are new geometric frustration system on tetrahedral lattice for d-electron spins.