Incommensurate Spin Density Wave versus local magnetic inhomogeneities in Ba(Fe1-xNix)2As2: a 57Fe Mossbauer spectroscopy study

We report 57Fe Mossbauer spectral results in pure and doped Ba(Fe1-xNix)2As2 with x=0.01 and 0.03. We show that all these materials present a first-order magnetic transition towards a magnetically ordered state. In the doped compounds, a broad distribution of Fe hyperfine fields is present in the magnetic phase. We successfully fit the Mossbauer data in Ba(Fe1-xNix)2As2 in the framework of two different models: 1) an incommensurate spin density wave; 2) a dopant-induced perturbation of the Fe polarization, recently proposed to interpret 75As NMR data in Ba(Fe1-xNix)2As2, which is valid only in the very dilute limit x=0.01. Moreover, we show here that these NMR data can also be successfully analysed in terms of the 'incommensurate model' for all doping contents by using the parameters obtained from the Mossbauer spectral analysis. Therefore it is not possible to rule out the presence of an incommensurate spin density wave on the basis of the 75As NMR data.