Magnetic structures of R2Fe2Si2C intermetallic compounds: Evolution to Er2Fe2Si2C and Tm2Fe2Si2C

The magnetic structures of Er2Fe2Si2C and Tm2Fe2Si2C (monoclinic Dy2Fe2Si2C-type structure, C2/m space group) have been studied by neutron powder diffraction, complemented by magnetization, specific heat measurements, and Er166 Mössbauer spectroscopy, over the temperature range 0.5 to 300 K. Their magnetic structures are compared with those of other R2Fe2Si2C compounds. Antiferromagnetic ordering of the rare-earth sublattice is observed below the Néel temperatures of TN=4.8(2)K and TN=2.6(3)K for Er2Fe2Si2C and Tm2Fe2Si2C, respectively. While Er2Fe2Si2C and Tm2Fe2Si2C have the same crystal structure, they possess different magnetic structures compared with the other R2Fe2Si2C (R = Nd, Gd, Tb, Dy, and Ho) compounds. In particular, two different propagation vectors are observed below the Néel temperatures: k=[12,12,0] (for Er2Fe2Si2C) and k=[0.403(1),12,0] (for Tm2Fe2Si2C). For both compounds, the difference in propagation vectors is also accompanied by different orientations of the Er and Tm magnetic moments. Although the magnetic structures of Er2Fe2Si2C and Tm2Fe2Si2C differ from those of the other R2Fe2Si2C compounds, we have established that the two magnetic structures are closely related to each other. Our experimental and first-principles studies indicate that the evolution of the magnetic structures across the R2Fe2Si2C series is a consequence of the complex interplay between the indirect exchange interaction and crystal field effects.