PRESSURE EFFECTS ON THE ELECTRONIC-PROPERTIES AND THE MAGNETIC GROUND-STATE OF GAMMA'-FE4N

The effects of pressure on the electronic properties and the magnetic ground state of gamma'-Fe4N have been investigated using both the Fe-5 7 Mossbauer effect (up to 6.1 GPa at 4.2 K) and X-ray diffraction (up to 8.0 GPa at 300 K) techniques. The analysis of the X-ray diffraction data under pressure shows a linear decrease of the volume with pressu re with a compressibility of 5.1(1) X 10(-3) GPa(-1). From the measure d difference (Delta S = 0.06 mm/s) between the isomer shifts of the Fe (I) and Fe(II) sites at ambient pressure, a charge transfer from N-2p to Fe(II)-3d is proposed. which is supported by recent band structure calculations. The pressure-induced decrease of S of Fe(I) and Fe(II) i s found to be nearly the same, indicating that the increase of the s-e lectron density at the Fe-57 nucleus is governed by the compression of the 4s-electrons rather than by charge transfers. Regarding the press ure dependence of the magnetic moments of the Fe(I) and Fe(II) sites, we find in contrast to the results of very recent high-pressure NMR ex periments on gamma'-Fe4N, which reveal almost a comparable pressure-in duced decrease of the Fe-57 NMR frequency of the two Fe sites, that th e magnetic hyperfine (hf) field (B-eff) at the Fe(I) site decreases mo re rapidly with pressure than that at the Fe(II) site. This finding is inconsistent with recent band structure calculations on gamma'-Fe4N w hich show that the magnetic moment of the Fe(I) site is more localized than that of the Fe(II) site. We suggest that this discrepancy betwee n theory and our experimental results is due to the contribution of a transferred hf field to the pressure dependence of B-eff, which is sen sitive to the variation of Fe-N interactions with pressure.