title: Investigation of the crystal structure and the structural and magnetic properties of SrCu2(PO4)2.
abstract: SrCu2(PO4)2 was prepared by the solid-state method at 1153 K. Its structure was solved by direct methods in the space group Pccn (No. 56) with Z = 8 from synchrotron X-ray powder diffraction data measured at room temperature. Structure parameters were then refined by the Rietveld method to obtain the lattice parameters, a = 7.94217(8) A, b = 15.36918(14) A, and c = 10.37036(10) A. SrCu2(PO4)2 presents a new structure type and is built up from Sr2O16 and Cu1Cu2O8 units with Cu1...Cu2 = 3.256 A. The magnetic properties of SrCu2(PO4)2 were investigated by magnetic susceptibility, magnetization up to 65 T, Cu nuclear quadrupole resonance (NQR), electron-spin resonance, and specific heat measurements. With spin-dimer analysis, it was shown that the two strongest spin-exchange interactions between Cu sites result from the Cu1-O...O-Cu2 and Cu2-O...O-Cu2 super-superexchange paths with Cu1...Cu2 = 5.861 A and Cu2...Cu2 = 5.251 A, and the superexchange associated with the structural dimer Cu1Cu2O8 is negligible. The magnetic susceptibility data were analyzed in terms of a linear four-spin cluster model, Cu1-Cu2-Cu2-Cu1 with -2J(1)/kB = 82.4 K for Cu1-Cu2 and -2J(2)/k(B) = 59 K for Cu2-Cu2. A spin gap deduced from this model (Delta/kB = 63 K) is in agreement with that obtained from the Cu NQR data (Delta/kB = 65 K). A one-half magnetization plateau was observed between approximately 50 and 63 T at 1.3 K. Specific heat data show that SrCu2(PO4)2 does not undergo a long-range magnetic ordering down to 0.45 K. SrCu2(PO4)2 melts incongruently at 1189 K. We also report its vibrational properties studied with Raman spectroscopy.
authors.affiliation: International Center for Young Scientists, National Institute for Materials Science, 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: Masaki
authors.initials: M
authors.lastname: Azuma
authors.forename: Akira
authors.initials: A
authors.lastname: Matsuo
authors.forename: Myung-Hwan
authors.initials: MH
authors.lastname: Whangbo
authors.forename: Hyun-Joo
authors.initials: HJ
authors.lastname: Koo
authors.forename: Jun
authors.initials: J
authors.lastname: Kikuchi
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Kaji
authors.forename: Susumu
authors.initials: S
authors.lastname: Okubo
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ohta
authors.forename: Koichi
authors.initials: K
authors.lastname: Kindo
authors.forename: Mikio
authors.initials: M
authors.lastname: Takano