Magnetism and Electronic States of X2Co12P7 (X = Ti, Zr and Hf).

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 T_C of which is approximately 150 K. As results of magnetization measurements, we found these compounds to show itinerant ferromagnetism with T_C = 67, 149 and 133 K for X = Ti, Zr and Hf, respectively. This behavior is in contrast to the case of Ln₂Co₁₂P₇ in which T_C is almost independent of Ln. The lower T_C 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 T_C 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. [ABSTRACT FROM AUTHOR]