Abstract
It is known that ACu2(PO4)2 (A=Ba, Sr) crystallizes into a triclinic structure and belongs to the P-1 space group. Cu2+ ions occupy four crystallographically different sites forming zigzag chains in the a-b plain. The A2+ ions separate Cu2+chains and the magnetic coupling along the c-axis is diminished due to PO4 tetrahedra. The spacing of the Cu2+ ions in a chain has sequence of - 3 . 8 0 Å - 3 . 6 0 Å - 3 . 4 7 Å - 3 . 5 8 Å- 3 . 8 0 Å - so that the four spins form a relatively isolated group. Based on the results of x-ray diffraction, it is expected that Sr compound has the same crystallographic structure as Ba compound. Results of magnetic susceptibility measurements of both Ba and Sr compounds suggest that both of them have a singlet ground state. A broad maximum in magnetic susceptibility was observed at 60 K for Ba and 40 K for Sr compounds. Experimental results for Ba compound were best fitting using the ladder model with energy gap of 33 K. On the other hand, experimental results of Sr compound were best fitting using 4 spin cluster model with j1/kB= 30 K and j2/kB= 40 K. The differences in the magnetic properties of these two compounds have been investigated by ESR technique.
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