Magnetic properties of CeCoSi and related compounds

Compounds represented by the chemical formula RTX (R: rare earths, T: transition metals, X: p-block elements) have various crystal structures from the monoclinic to cubic system depending on the combination of elements. Among them, CeCoSi crystallizes into the tetragonal CeFeSi-type structure, and has attracted much attention in recent years. At low temperatures, CeCoSi successively exhibits two phase transitions. One is an antiferromagnetic ordering of Ce-4f electron at T=9.4 K, and the other is a “hidden” ordering at T~12 K. At present, a possibility of an antiferroquadrupole ordering of Ce-4f electron accompanied by so-called odd-parity multipole degrees of freedom have been proposed. Detailed research is needed for comprehensive understanding of the hidden order. We have recently expanded the research to related compounds with the same CeFeSi-type structure. Sample syntheses and their magnetic properties will be presented.