Critical spin fluctuations in the two-dimensional antiferromagnet KFeF4: A Mössbauer study

Abstract

The critical spin fluctuations in the two-dimensional antiferromagnet KFeF4 were investigated above TN=136.15 K in detail by means of Fe57 Mössbauer spectroscopy. Evidence is given that the critical dynamics of KFeF4 falls within the dynamic universality class (d,n)=(2,1). The dynamic critical exponent z was deduced from the longitudinal spin-autocorrelation time in the reduced temperature range 4×10-4<t<10-1. It is shown that the dynamic critical behavior of KFeF4 is in agreement with conventional theory (z=1.75) with z=1.77(5) down to at least t 5×10-3. However, closer to TN our data seem to indicate a small deviation from conventional behavior with z=1.54(6). Possible reasons for this deviation are discussed. © 1984 The American Physical Society.