Statistical mechanics and critical behavior of the magnetoelectric effect in GdVO4

Utilizing the magnetoelectric (ME) effect, the magnetic space group of GdVO4 has been determined to be I41′a′m′d. The temperature dependence of the ME susceptibility α was measured from 1.6°K to TN=2.43°K. Using a modified molecular-field theory it is concluded, from the temperature dependence of α, that the mechanism(s) underlying the effect can be an electric-field-induced Dzialoshinsky interaction and/or an electric-field-induced g shift. The magnitude of α indicates that the former mechanism is the more likely one. The critical behavior of α was measured in the range 0.977TTN0.999. A critical exponent of β=0. 50±0.05 was found. This is considerably higher than that expected for a three-dimensional two-sublattice Heisenberg model with nearest-neighbor interactions only and is suggestive of higher than first-neighbor exchange interactions which act to enhance the long-range order of the system. Such interactions could have a significant effect on the critical behavior due to the small number of nearest neighbors on the diamond lattice formed by the Gd3+ moments.