Investigation of the Crystal Structure and the Structural and Magnetic Properties of SrCu2(PO4)2

• Published in: Inorganic chemistry 2005-09, Vol.44 (19), p.6632-6640
• Main Authors: Belik, Alexei A, Azuma, Masaki, Matsuo, Akira, Whangbo, Myung-Hwan, Koo, Hyun-Joo, Kikuchi, Jun, Kaji, Tomoyuki, Okubo, Susumu, Ohta, Hitoshi, Kindo, Koichi, Takano, Mikio
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic051079h

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) Å, b = 15.36918(14) Å, and c = 10.37036(10) Å. SrCu2(PO4)2 presents a new structure type and is built up from Sr2O16 and Cu1Cu2O8 units with Cu1···Cu2 = 3.256 Å. 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 Å and Cu2···Cu2 = 5.251 Å, 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/k B = 82.4 K for Cu1−Cu2 and −2J 2/k B = 59 K for Cu2−Cu2. A spin gap deduced from this model (Δ/k B = 63 K) is in agreement with that obtained from the Cu NQR data (Δ/k B = 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.