Magnetic phase transitions in SmCoAsO

Magnetization, x-ray diffraction, and specific-heat measurements reveal that SmCoAsO undergoes three magnetic phase transitions. A ferromagnetic transition attributed to the Co ions, emerges at T(C)=57 K with a small saturation moment of similar to 0.15 mu(B)/Co. Reorientation of the Co moment to an antiferromagnetic state is obtained at T(N2)=45 K. The relative high paramagnetic effective moment P(eff)=1.57 mu(B)/Co indicates an itinerant ferromagnetic state of the Co sublattice. The third magnetic transition at T(N1)=5 K is observed clearly in the specific-heat study only. Both magnetic and (57)Fe Mossbauer studies show that substitution of small quantities of Fe for Co was unsuccessful.