Magnetic properties of layered compounds LnCoAsO (Ln = lanthanoids) with itinerant-electron ferromagnetism

We synthesized polycrystalline samples of layered compounds LnCoAsO (Ln = La - Gd) and measured magnetization of the samples, especially, in the cases of Ln = Nd, Sm and Gd, which show ferromagnetic-antiferromagnetic transitions (FAFT). From the results of magnetic measurements, we successfully draw the magnetic phase diagrams of these compounds. We showed that the FAFT temperatures TN at various magnetic fields in the cases of Ln = Nd and Sm well scale to the de Gennes factors of the trivalent ions of Nd and Sm, showing that the Ruderman-Kittel-Kasuya-Yoshida interaction is the origin of the FAFT in these compounds. We also draw the total magnetic phase diagram of LnCoAsO (Ln = La - Gd).