Anomalous magnetization in the layered itinerant ferromagnet LaCoAsO

We synthesized weakly itinerant ferromagnet with layered structure LaCoAsO and measured the isothermal magnetizations at various temperatures. The isothermal magnetizations in a form of Arrott plot for weakly itinerant ferromagnets such as ZrZn2, Sc3In, Ni3Al, and Y(Co,Al)(2) shows parallel linear relation over the wide temperature range near the Curie temperature T-C, while for LaCoAsO the square of the magnetization M-2 was found to show a convex curvature against H/M, similar to MnSi and FexCo1-xSi. We analyzed the magnetization of LaCoAsO at T-C and estimated several parameters of spin fluctuations on the basis of self-consistent renormalization theory of spin fluctuations. We simulated a reciprocal magnetic susceptibility above T-C and discussed the nature of spin fluctuations in LaCoAsO.