The Order Parameter for the Incommensurate Transition in K₂SeO₄: an EPR Lineshape Study

Abstract

The EPR lineshape of the SeO₄⁻ center was investigated in the normal-incommensurate transition of K₂SeO₄. The value β=0.33±0.03 was obtained for the critical exponent of the order parameter. A summary of the measured values of the critical exponent β found in the literature for structurally incommensurate systems is presented. The average value of those measurements, β=0.345±0.004, is in excellent agreement with the calculated value of β for the 3d XY model. The lineshape analysis seems also to indicate that phase solitons appear in a large region of the incommensurate phase.