Coexistence of charge density wave and antiferromagnetism in Er₅Ir₄Si₁₀

Abstract

Er₅Ir₄Si₁₀ exhibits three phase transitions upon cooling below room temperature. At T_CDW=151 K a combined commensurate and incommensurate superstructure develops, that has been attributed to the formation of charge density waves (CDWs). At T_LI=60 K (LI=lock-in) the superstructure becomes commensurate, and at T_N=2.8 K a state with long-range antiferromagnetic order develops. In this contribution we report the results of high-intensity, high-resolution x-ray diffraction for the temperature region encompassing all four phases. We have found that above T_CDW the critical scattering of the commensurate superlattice reflections persists up to much higher temperatures than the critical scattering of the incommensurate satellites. It is argued that this finding substantiates the hypothesis in which the mechanism of the CDW transition involves a structural transition towards a twofold superstructure. The superlattice reflections are found to be broader in the lock-in phase than above T_LI. This suggests that the lock-in transition results in relatively small domains, that are responsible for the broadening of the reflections. Finally, the antiferromagnetic order is observed by resonant x-ray scattering. The commensurate superlattice reflections persist down to 1.87 K, and no effect of the magnetic transition on their positions or intensities is found. Thus the magnetic order and the CDW coexist below T_N in this compound.