Anomalous magnetization in the layered itinerant ferromagnet LaCoAsO

Abstract

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 ${\text{ZrZn}}_{2}$, ${\text{Sc}}_{3}\text{In}$, ${\text{Ni}}_{3}\text{Al}$, and $\text{Y}{(\text{Co},\text{Al})}_{2}$ shows parallel linear relation over the wide temperature range near the Curie temperature ${T}_{\text{C}}$, while for LaCoAsO the square of the magnetization ${M}^{2}$ was found to show a convex curvature against $H/M$, similar to MnSi and ${\text{Fe}}_{x}{\text{Co}}_{1\ensuremath{-}x}\text{Si}$. We analyzed the magnetization of LaCoAsO at ${T}_{\text{C}}$ 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 ${T}_{\text{C}}$ and discussed the nature of spin fluctuations in LaCoAsO.