Effects of Pressure and a Magnetic Field on Chromium Studied by Neutron Diffraction

Abstract

In addition to decreasing the first-order antiferromagnetic-to-paramagnetic phase change near 312°K, pressure also decreases the spin-flip transformation near 122°K, and appears to decrease the amplitudes of the static magnetization waves. By means of neutron diffraction we have determined the initial derivatives of these pressure variations using small pressures up to 100 atm. Magnetic fields applied to samples while cooling through the 312°K transition produce crystals whose magnetic structure can be ascribed to a single fundamental wavevector. This state, however, is not single domain. A model has been proposed previously by two of the authors (S.A.W. and A.A.) for this state in which the crystal spontaneously breaks up into many small domains in each of which the polarization axis is thermally excited. The predictions of this model have been checked by studying the field dependence (to 27 kG) of the mean directions of the polarizations and how this varies with temperature. The agreement between the experiments and the model is good. Small hysteresis effects as a function of magnetic field have also been observed. A magnetic field of 27 kG applied parallel to the wavevector decreases the spin-flip temperature 1°K but does not affect the Néel temperature.