Magnetic properties of alkaline earth and lanthanoid iron antimonides AFe(4)Sb(12) (A=Ca,Sr,Ba, La-Nd,Sm,Eu) with the LaFe4P12 structure

The magnetic properties of the nine title compounds were studied by magnetic susceptibility measurements with a SQUID magnetometer between 2 and 300K. At temperatures above 100K, all compounds with the exception of the cerium and samarium compounds show Curie-Weiss behaviour. The effective magnetic moments of the alkaline earth compounds vary between 3.7 +/- 0.2 mu(B) and 4.0 +/- 0.2 mu(B) per formula unit. For LaFe4Sb12 the moment is smaller (3.0 +/- 0.2 mu(B)) indicating a higher degree of electronic saturation within the Fe4Sb12 polyanion. At lower temperatures, the magnetic susceptibilities of these compounds deviate from the Curie-Weiss law, however, they remain field independent. A mixed valent behaviour is observed for the cerium compound and the samarium compound reflects the Van Vleck paramagnetism of the Sm3+ ions. The magnetic susceptibilities of the other lanthanoid compounds correspond to the sums of the susceptibilities of the Fe4Sb12 polyanion and the Ln(3+) and EU(2+) ions, respectively. These antimonides order ferromagnetically with Curie temperatures varying between 5(1)K for PrFe4Sb12 and 82(2) K for EuFe4Sb12. The magnetic properties of these compounds are discussed within the framework of a rigid band structure.