Itinerant Ferromagnetism and Metamagnetism in Cr Doped Perovskite   Ruthenates
  We report results of structural, magnetic and transport properties of single crystal CaRu1-xCrxO3 (0&#8804;x&#8804;0.36) and SrRu1-xCrxO3 (0&#8804;x&#8804;0.30). Cr substitution as low as x=0.08 drives CaRu1-xCrxO3 from the paramagnetic state to an itinerant ferromagnetic state with field-driven first-order metamagnetic transitions leading to a sizeable saturation moment (~0.4&#61549;B/f.u.within the ab plane). The ferromagnetism occurs abruptly and reaches as high as TC=123 K for x=0.22. The Cr-driven ferromagnetism is highly anisotropic, suggesting an important role for spin-orbit coupling. Lattice constant and magnetic measurements strongly support the valence of the Cr as tetravalent (Cr4+, 3d2 configuration). Cr substitution for Ru in SrRuO3 (TC=165 K) enhances the itinerant ferromagnetism, with TC reaching 290 K for x=0.30, consistent with Cr-induced ferromagnetism in paramagnetic CaRuO3. Preliminary pressure-dependent magnetization of CaRu0.85Cr0.15O3 shows strong enhancement of the saturation magnetization (25% for P~0.7 GPa). All results indicate a coupling of Ru 4d and Cr 3d electrons that is unexpectedly favorable for itinerant ferromagnetism which often exists delicately in the ruthenates. 
V. Durairaj, E. Elhami, S. Chikara, X.N. Lin, A. Douglass, G. Cao P.   Schlottmann, E. S. Choi and R. P. Guertin