Magnetic study of SmCoAsO showing a ferromagnetic-antiferromagnetic transition

Abstract

We synthesized a polycrystalline sample of SmCoAsO and measured its magnetization $(M)$ at various of temperatures $(T)$ and magnetic fields $(H)$. As decreasing $T$, a paramagnetic to ferromagnetic transition occurs at 70 K, and then a ferromagnetic to antiferromagnetic transition occurs at 42 K. In the antiferromagnetic phase, we observed the behavior characteristic of metamagnetic transitions in $M\text{\ensuremath{-}}H$ curves. From the results of magnetization measurements up to $H=56\text{ }\text{T}$, we successfully draw the magnetic phase diagram of SmCoAsO. We observed convex behavior in Arrott plots in the ferromagnetic temperature region as seen in MnSi, ${\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$, and isostructural compound LaCoAsO. We discussed the magnetic property of SmCoAsO above ${T}_{\text{C}}$ based on the spin-fluctuation theory.