NEUTRON-DIFFRACTION INVESTIGATION OF THE H-T PHASE-DIAGRAM OF ALPHA-FE2O3

The phase boundary between the low temperature antiferromagnetic and the weak ferromagnetic state of α‐Fe2O3 (hematite) is established from neutron diffraction measurements on a single crystal. Magnetic fields up to 80 kOe are applied perpendicular to the trigonal axis. From the induced rotation of the antiferromagnetic component of the magnetization the critical fields H1/c are derived in the temperature range from 220 K to the Morin transition at (259.7 ± 0.3) K. The boundary is shown to be linear with a slope of –(1.73 ± 0.05) kOe/K, which gives a latent heat of (9.43 ± 0.27) × 105 erg/cm3 for the Morin transition in hematite. These results support the Dzyaloshinskii theory and agree with previous measurements. The “low‐field” data however give at zero field a residual angle of inclination of the moments with the unique axis. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA