MAGNETOELECTRIC EFFECT IN THE SPIN-FLOP PHASE OF CR2O3 AND THE PROBLEM OF DETERMINING THE MAGNETIC-STRUCTURE

The magnetoelectric effect has been studied in the spin-flop phase of Cr2O3 in pulsed magnetic fields up to 200 kOe over the temperature ran ge 4.2-300 K. It is shown theoretically that the coefficient alpha33 i n this phase is described as a function of the components of the antif erromagnetism vector by alpha33 = chi(perpendicular-to) lambda6 L(y)(L (y)2-3L(x)2). In other words, this coefficient is relativistically sma ll in comparison with other components of the magnetoelectric tensor. An experiment involving a careful orientation of the magnetic field wi th respect to the c axis of the crystal revealed alpha33 congruent-to 0, within the experimental error. Possible reasons for a nonzero obser ved value of alpha33 are discussed.