Domain-based magnetoelectric studies for single crystals of chromium oxide

Abstract

As is well known, the sign of parallel magnetoelectric susceptibility for chromium oxide can be positive or negative both depending on prehistory of the sample, but it is always opposite to the perpendicular susceptibility. In order to explain this behaviour, the concept of antiferromagnetic domains depending on the existence of two possibilities spin orientation in a magnetic unit cell was invoked both by Rado and Astrov. The authors have carried out detailed studies of domain-based magnetoelectric effect for Cr 2O 3 and the results are presented in this communication. Investigations were carried out both for static and dynamic effect. For static measurements the dielectric constant method developed earlier has been used. The domain pattern in the sample is altered by cooling in simultaneous presence of different electric ( E) and magnetic ( B) fields from paramagnetic state to the ordered state, and the magnetoelectric susceptibility evaluated. From the measurements it is concluded that the deciding parameter of magnetoelectric susceptibility if product of fields EB for low fields as reported by Martin and Anderson. For high fields, the electric field seems to play a more significant role, and magnetoelectric susceptibility is a function of E 2 B used for cooling. Static measurements are also extended to low temperatures for parallel susceptibility for the sample with largest magnetoelectric susceptibility. In the temperature range used (90 K to room temperature) the change in susceptibility observed is not very significant, a fact which is hard to explain. Data about the effect of variation of cooling rate and step function cooling is also presented, and it is concluded, though not in a definite manner, that rectangular step function cooling is as effective as continuous rate cooling in deciding magnetoelectric susceptibility of the sample. For dynamic studies, again the dielectric constant method is used, and measurements are reported at different frequencies for a sample with possibly a large number of domains. Two resonant peaks in the dielectric constant are observed and they are tentatively explained on the basis of domain wall resonance.