title: Magnetic properties of synthetic libethenite Cu2PO4OH: a new spin-gap system.
abstract: Synthetic mineral libethenite Cu(2)PO(4)OH was prepared by the hydrothermal method, and its structure at 200 K was refined by single-crystal X-ray diffraction. The structure of Cu(2)PO(4)OH is built up from Cu2(2)O(6)(OH)2 dimers of edge-sharing Cu2O(4)(OH) trigonal bipyramids and [Cu1(2)O(6)(OH)(2)] proportional chains of edge-sharing Cu1O(4)(OH)(2) octahedra. Magnetic properties of Cu(2)PO(4)OH were investigated by magnetic susceptibility, magnetization, and specific heat measurements. Cu(2)PO(4)OH is a spin-gap system with a spin gap of about 139 K. It was shown by spin dimer analysis that, to a first approximation, the magnetic structure of Cu(2)PO(4)OH is described by an isolated square-spin cluster model defined by the Cu1-O-Cu2 superexchange J with Cu1...Cu2 = 3.429 A. The fitting analysis of the magnetic susceptibility data with a square-spin cluster model results in J/k(B) = 138 K. Specific heat data show that Cu(2)PO(4)OH does not undergo a long-range magnetic ordering down to 1.8 K. We also report vibrational properties studied with Raman spectroscopy and the thermal stability of Cu(2)PO(4)OH.
authors.affiliation: Advanced Nano Materials Laboratory (ANML), International Center for Young Scientists (ICYS), and Quantum Beam Center, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan. alexei.belik@nims.go.jp
authors.forename: Alexei A
authors.initials: AA
authors.lastname: Belik
authors.forename: Hyun-Joo
authors.initials: HJ
authors.lastname: Koo
authors.forename: Myung-Hwan
authors.initials: MH
authors.lastname: Whangbo
authors.forename: Naohito
authors.initials: N
authors.lastname: Tsujii
authors.forename: Pance
authors.initials: P
authors.lastname: Naumov
authors.forename: Eiji
authors.initials: E
authors.lastname: Takayama-Muromachi