Magnetic properties of LCoAsO (L=La-Gd)

We synthesized a series of CoAs based weakly itinerant ferromagnetic compound LCoAsO (L: lanthanoids) and systematically studied a L dependence on magnetic properties. Lattice constants a and c decrease monotonically with the decrease in the ion size of L3+. In the cases of L=Nd, Sm, and Gd, a ferromagnetic-antiferromagnetic transition was observed at T-N=15, 35, and 75 K, respectively, indicating the existence of unconventional interaction between ferromagnetically ordered itinerant electrons of Co. The Curie temperature T-C increases from 55 to 75 K by changing La to Ce while from Ce to Gd the T-C does not change so much, being quite similar to the L site dependence of the superconducting transition temperature T-c in FeAs-based high-T-c compound LFeAsO. We discussed the mechanism of ferromagnetic-antiferromagnetic transition and the lanthanoid dependence of T-C.