Magnetic phase diagram of Pr_1-xLa_xFe ₄P₁₂ (0 ≤ x ≤ 0.15)

We report measurements of the dc magnetization of a series of Pr _1-xLa_xFe₄P₁₂ single crystals (0 ≤ x ≤ 0.15). The nonmagnetic order (A phase) evolves to a short-range one at a very small La concentration of about 3%, above which ferromagnetic ordering occurs. Both the ferromagnetic transition temperature and spontaneous magnetization increase abruptly above x > 0.03, although the Weiss temperature decreases substantially with increasing x. These results suggest a competition between the A phase and ferromagnetic state, and the role of Fermi surface nesting on the A phase transition is emphasized. The effect of La impurities on the high-field ordered state (B phase) in the [111] direction is also presented.