A search for defect related ferromagnetism in SrTiO3

Room temperature ferromagnetic hysteresis is observed in commercial SrTiO3 substrates purchased from a variety of suppliers. It is shown that the ferromagnetic signal comes from the unpolished surfaces. Surface impurity phases cannot be detected using either x-ray diffraction or energy dispersive x-ray spectra on the unpolished surfaces. However, a possible correlation between surface disorder (x-ray diffraction peak linewidth) and ferromagnetism is observed. Ar ion bombardment (10-90 keV) can be used to produce surface layer disorder but is not found to induce ferromagnetism. Annealing of the substrates at temperatures ranging from 600 to 1100 degrees C is found to alter the hysteresis curves differently depending on whether the annealing is performed in air or in vacuum. Identical annealing behavior is observed if the substrates are artificially spiked with iron. This suggests that the ferromagnetic hysteresis of as purchased SrTiO3 could be due to Fe contamination of the unpolished surfaces. In addition, it is shown that no ferromagnetism is observed in samples that contain 10(19)-10(21) cm(-3) of oxygen vacancies if all the faces are polished. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3481344]