Long Range Magnetic Order in Boron Icosahedral Cluster Compounds

Abstract

Magnetic properties of rare earth B₁₂ icosahedral cluster compounds such as REB₅₀ have attracted growing interest because magnetic transitions have been discovered at moderate temperatures despite the non-metallic and magnetically dilute nature of the compounds and the indication that B₁₂ clusters mediate the interaction.It has also been reported in Nature etc. that Ca_1-xLa_xB₆ exhibits high temperature ferromagnetism, but we have demonstrated this magnetism to be of non-intrinsic origin. We have also discovered a class of trigonal and rhombohedral B₁₂ compounds such as REB₂₂C₂N to exhibit spin glass behavior. Low temperature magnetic properties of single crystals of the new B₁₂ cluster compound GdB₁₈Si₅ (R-3m) were investigated. An antiferromagnetic transition is observed at 3.2 K and it is indicated this compound exhibits the first long range magnetic order ever observed in B₁₂ cluster systems. A striking feature of the indicated order is that the rare earth atoms have partially occupied sites.