Successive Magnetic Transitions in RECoAsO

In order to elucidate the details of successive magnetic transitions in the rare earth cobalt arsenic oxides (RECoAsO), 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 into abulk static ferromagnetic ordered phase below around 70 K(=TC). Furthermore, additional transitions into a static antiferromagnetic ordered phase were found for the RE = Nd, Sm, and Gd compounds; namely TN1 = 15 K and TN2 = 7 K for Nd, TN1 = 41.5 K and TN2 = 17.5 K for Sm, and TN = 3K for Gd.