Incommensurate-commensurate lock-in phase transition in EuAs₃

We have investigated the incommensurate-commensurate lock-in phase transition in EuAs₃ by the relatively new resonant X-ray magnetic scattering technique. Strong resonance enhancements of the magnetic scattering have been observed at the L_II and L_III absorption edges of Eu. The intensity of the 1, 0, 5/2 magnetic reflection of the commensurate phase decreases continuously with increasing temperature and at T_L = 10.3 K drops abruptly to zero. Satellite reflections characteristic of the incommensurate phase appear at T ≥ T_L. By using the excellent Q-resolution of the X-ray magnetic scattering experiment we have determined the temperature variation of both x and z components of the propagation vector of the incommensurate sine-wave phase stable in the temperature range 10.3 K ≤ T ≤ 11 K.