Experimental determination of the mechanism of ME effect of Cr2O3 from ME susceptibility and electric shift in the antiferromagnetic resonance

The mechanisms of the ME effect of Cr2O3 were experimentally determined at 4.2 K. For this purpose, ME susceptibility was measured statically by SQUID from 1.6 to 270 K and the electric shift of AFMR was observed at 4.2 K by an ac modulation method. The former experiment gave α∥(4.2 K) =−0.8, α∥(255 K) =15.3 and α⊥(4.2 K) =−4.7 in 10−4 cgs unit. The latter gave a frequency shift of −1.02×10−6 cm−1 at E=1 cgs in the case of both E↘ and H↘ parallel to the c axis. From these experiments, δg=−1.05×10−8 and δD=−3.3×10−6 cm−1 were deduced for E=1 cgs along the c axis. This value is not only too small but of the wrong sign to explain the sign and the magnitude of α∥ at higher temperatures. α⊥ at 4.2 K seems too large to be interpreted by the tilting of the easy axis of spins and the role of other mechanisms such as the appearance of a Dzyaloshinski interaction is suggested.