Spin fluctuations in doped antiferromagnetic K2FeF5

Abstract

At 1.3 K the Mossbauer spectra of the typical quasi-1D antiferromagnet K2FeF5 which orders at 6.95 K, consist of a single narrow sextet with a hyperfine field significantly reduced from the free ion value by zero-point spin fluctuations. When some of the iron sites are substituted with small amounts of (nonmagnetic) gallium, the lines become asymmetrically broadened and the mean hyperfine field is further reduced. It is shown that the spectra of the doped samples can be well simulated by a simple model of zero-point spin reduction for the finite chains produced by doping. It is suggested that, though the simulation would be more complicated, quantum fluctuations associated with surface or edge effects may also contribute to the line broadening at low temperatures in other finite systems, such as ferrimagnetic or antiferromagnetic superparamagnets.