Effect of Pressure on the Isomer Shift ofFe57in the bcc Phase

The effect of pressure to 130 kbar has been measured on the isomer shift of bcc iron, using the inner two lines of the magnetically split six-line iron spectrum. The isomer shift is nearly linear in pressure to about 60 kbar; at higher pressures the rate of shift to higher electron density is less. The data are not linear with volume in the higher-pressure region either. The results are interpreted in terms of Ingalls's discussion of the transfer of electrons from the $4s$ to the $3d$ bands and the value of the proportionality constant between the isomer shift and the square of the wave function. The change in magnetic field with pressure is discussed very briefly.