Antiferromagnetism in hcp Iron-Manganese Alloys

Abstract

Antiferromagnetism in hcp Fe-Mn alloys (17.8, 25.9 and 28.6 at %Mn) was investigated by means of Mössbauer effect and neutron diffraction measurements. Néel temperatures and internal magnetic fields at 0°K were determined to be 230°K and 16 kG, respectively, over the composition range of the measured alloys. Consequently, hcp alloys have weaker internal magnetic fields and lower Néel temperatures than the fcc modifications. In the neutron diffractions on powder and sheets with preferred orientation of hcp Fe _0.714 Mn _0.289 , only (001) magnetic reflection was found. The averaged magnetic moment was evaluated to be 0.25 µ _B assuming the antiferromagnetic stacking of ferromagnetic (001) sheets. Isomer shifts relative to bcc Fe and quadrupole splittings of hcp alloys are extrapolated to the zero Mn concentration to be -0.20 mm/sec and 0.14 mm/sec, respectively. The results are discussed in connection with magnetism in hcp Fe.