2018 年 65 巻 5 号 p. 274-278
To elucidate magnetism and electronic states of X2Co12P7 with X = Ti, Zr and Hf, which are expected to be in a tetravalent state or a trivalent state with one d-electron, we measured magnetizations of polycrystalline samples of X2Co12P7 and compared their magnetic behaviors with that of itinerant ferromagnets Ln2Co12P7 (Ln = lanthanoids), the Curie temperature TC of which is approximately 150 K. As results of magnetization measurements, we found these compounds to show itinerant ferromagnetism with TC = 67, 149 and 133 K for X = Ti, Zr and Hf, respectively. This behavior is in contrast to the case of Ln2Co12P7 in which TC is almost independent of Ln. The lower TC for the case of X = Ti compared with Ln2Co12P7 suggests that the valence of Ti in this compound is +4 rather than +3 and ferromagnetism derived from Co is weakened due to the electron doping from Ti. On the other hand, in the case of X = Zr and Hf compounds, both TC have similar values to that for Ln2Co12P7, indicating that X are almost in the trivalent state. From the result of magnetization measurements, it is clear that there is no localized magnetic moment in these compounds. Therefore, d-electrons in trivalent Zr or Hf show itinerant nature in X2Co12P7.