12 th International Conference on Muon Spin Rotation, Relaxation and Resonance Successive magnetic transitions in RECoAsO

AbstractInordertoelucidatethedetailsofsuccessivemagnetictransitionsintherareearthcobaltarsenicoxides( RE CoAsO),we have measured muon-spin rotation and relaxation (μ + SR) spectra of powder samples with RE =La, Ce, Pr, Nd,Sm, and Gd. Together with the result of magnetization measurements, it was found that all the compounds enter intoa bulk static ferromagnetic ordered phase below around 70 K (= T C ). Furthermore, additional transitions into a staticantiferromagnetic ordered phase were found for the RE =Nd, Sm, and Gd compounds; namely T N1 =15 K and T N2 =7 K for Nd, T N1 =41.5 K and T N2 =17.5 K for Sm, and T N =3 K for Gd. Keywords: , Pnictides and chalcogenides, Antiferromagnetics, Other ferromagnetic metals and alloys, Muon-spinrotation and relaxation1. IntroductionAlthough LaFeAsO enters into an itinerant spin-density-wave (SDW) antiferromagnetic (AF) phase below T N ∼140 K [1, 2], LaCoAsO (LaCoPO) is an itinerant ferromagnet with T C =60 K (50K) down to the lowest T measured[3]. Recently, Ohta