The magnetic, electronic, and structural properties of the solid solutions LaxSr1−xRuO3 and LaxCa1−xRuO3 have been studied by 99Ru Mössbauer spectroscopy and other techniques. The LaxCa1−xRuO3 phases are reported for the first time and have been shown by powder X-ray diffraction measurements to be orthorhombically distorted perovskites. Electrical resistivity measurements on compacted powders show that all the phases are metallic with p ∼ 10−3, ohm-cm.
Progressive substitution of Sr2+ by La3+ in ferromagnetic SrRuO3 leads to a rapid collapse of the magnetic hyper-fine splitting at 4.2°K. For x = 0.25 some ruthenium ions still experience a magnetic field but for 0.4 â©½ x â©½ 0.75 only single, narrow resonance lines are observed, consistent both with the complete removal of the ferromagnetism and with the presence of an averaged ruthenium oxidation state in each phase, i.e., Lax3+Sr1−x2+Ru(4−x)+O3 rather than Lax3+Sr1−x2+Rux3+Ru1−x4+O3. LaRuO3 and CaRuO3 both give essentially single-line spectra at 4.2°K, indicating that the ruthenium ions in these oxides are not involved in long-range antiferromagnetic order but are paramagnetic.
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