Search for Magnetic Ordering in hcp Iron

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Abstract
Mössbauer spectroscopy has been used to study the effects of high pressure and low temperature on the properties of bcc and hcp metallic iron. There is considerable evidence which indicates hcp iron should order antiferromagnetically at low temperatures. A search was made to 20 °K at 148 kbar and 48 °K at 176 kbar. No evidence was found for magnetic ordering. However, the hcp-iron resonance line was definitely broader than the inner two bcc resonance lines at all temperatures. The latter can be accounted for by self-adsorption broadening and a quadrupole splitting of 0.17 ± 0.03 mm/sec which is attributed to small quadrupole interactions in hcp iron. Results are presented on the pressure and temperature dependence of the isomer shift and second-order Doppler shift of bcc and hcp iron as well as on the hyperfine field of bcc iron. The effect of pressure on the second-order Doppler shift has been clearly observed and a characteristic Debye temperature of (545 ± 25)°K is found for hcp iron at 145 kbar. In addition, evidence is presented for a hysteresis associated with the bcc ↔ hcp transformation.