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 TC =57 K with a small saturation moment of ∼0.15 μB/Co. Reorientation of the Co moment to an antiferromagnetic state is obtained at TN₂ =45 K. The relative high paramagnetic effective moment Peff =1.57 μB/Co indicates an itinerant ferromagnetic state of the Co sublattice. The third magnetic transition at TN₁=5 K is observed clearly in the specific-heat study only. Both magnetic and F 57 e Mossbauer studies show that substitution of small quantities of Fe for Co was unsuccessful.