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Study of the Morin transition in nearly perfect crystals of hematite by diffraction and topography

1991; Elsevier BV; Volume: 168; Issue: 4 Linguagem: Inglês

10.1016/0921-4526(91)90057-l

1873-2135

V. V. Kvardakov, J. Sandonís, К. М. Подурец, S.Sh. Shilstein, J. Baruchel,

Magnetic properties of thin films

The spin reorientational magnetic Morin transition is investigated on nearly perfect crystals of hematite by combining neutron diffraction, neutron and synchrotron radiation topography, and magnetization measurements. The samples are platelet shaped crystals, with their main surface parallel to the (1 1 1) basal plane. The magnetization measurements show that the main part of the transition occurs over a rather narrow temperature range (about 3 K), whereas this range appears broadened to about 13 K on the neutron diffraction curves. Neutron topographs show the whole crystal image during transition and X-ray topographs show zone contrast when modifying the applied magnetic field. These experimental facts indicate that the interfaces which separate the weakly ferromagnetic and the antiferromagnetic phases are parallel to the main surfaces of the crystals. This is the basis for a very simple model which explains, through severe extinction effects, the apparent contradiction between neutron diffraction and magnetization measurements, and leads to an estimation of the crystal perfection parameters.