Weak ferrimagnetism and multiple magnetization reversal in alpha-Cr(3)(PO(4))(2)

Abstract

The chromium(II) orthophosphate alpha-Cr(3)(PO(4))(2) is a weak ferrimagnet with the Curie temperature T(C) = 29 K confirmed by a lambda-type peak in specific heat. Dominant antiferromagnetic interactions in this system are characterized by the Weiss temperature Theta = 96 K, indicating an intermediate frustration ratio vertical bar Theta vertical bar/T(C) similar to 3. In its magnetically ordered states alpha-Cr(3)(PO(4))(2) exhibits a remarkable sequence of temperature-induced magnetization reversals sensitive to the protocol of measurements, i.e., either field-cooled or zero-field-cooled regimes. The reduction of the effective magnetic moment 4.5 mu(B)/Cr(2+), as compared to the spin-only moment 4.9 mu(B)/Cr(2+), cannot be ascribed to the occurrence of the low-spin state in any crystallographic site of the Jahn-Teller active 3d(4) Cr(2+) ions. X-ray absorption spectra at the K edge indicate divalent chromium and unravel the high-spin state of these ions at the L(2,3) edges. Weak ferrimagnetism and multiple magnetization reversal phenomena seen in this compound could be ascribed to incomplete cancellation and distortion of partial spontaneous magnetization functions of Cr(2+) in its six crystallographically inequivalent positions.