Some new ternary ferromagnets (abstract)

A number of new ternary ferromagnetic compounds have been prepared¹ which have the general formula A_{1 4}MnX_{1 1} (A=Ca, Sr and X=As, Sb, or Bi) and are isostructural to the main group Zintl compounds Ca_{1 4}GaAs_{1 1} (Ref. 2) and Ca_{1 4}AlSb_{1 1}.³ The Mn-Mn nearest-neighbor distances in these compounds are ≥11 Å. Each of the compounds containing Mn is a metallic ferromagnet with a Curie transition in the neighborhood of 40–60 K. From magnetization measurements in the paramagnetic regime it appears that the Mn has a valence of +3 and that there are good local moments associated with the four unpaired electrons. This is in contrast to the low-temperature state in which the ordered ferromagnetic moment is only about 2.5 μ_B/Mn. Since no structural change is found upon cooling the sample below the Curie temperature and resistivity measurements show a strong interaction between the conduction electrons and the local moments, we suggest that the ferromagnetic moment is reduced by coupling with the conduction electrons.