Precursor symmetry breaking in Cr doped V2O3

Abstract The results of X-ray resonant scattering experiments performed on a (V 1− x Cr x ) 2 O 3 sample with x =0.028 are reported. This compound undergoes a first-order phase transition from paramagnetic insulator (PI) to antiferromagnetic insulator (AFI) at T N ≃181 K . At the same temperature a lattice distortion reduces the symmetry from R 3 c in the PI phase to I2/a in the AFI phase. To get more insight into the transition driving mechanism, we studied the behaviour of the Bragg forbidden peak (0 03) h ≡(1 0 1 ) m , at V K edge, as a function of temperature, polarization, azimuthal angle and X-ray energy. On the contrary to what observed in the pure system and to what expected theoretically a non-vanishing signal is observed already at room temperature in the dipolar channel.